2009. "Analysis of the High-Resolution Infrared Spectrum of Cyclopropane." Journal of Molecular Spectroscopy 255(1):45-55. Abstract The high resolution infrared spectrum of cyclopropane (C3H6) has been measured from 100 cm-1 to 2200 cm-1. In that region we have identified 24 absorption bands attributed to 6 fundamental bands, 5 combination bands, 3 hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, 4 and 14. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations 7, 9, 10, 11 are also reported. The spectral resolution of the measurements varied from 0.002 cm-1 to 0.004 cm-1.
2009. "On the Determination of C0 (or A0), D0K, H0K, and Some Dark States for Symmetric-top Molecules from Infrared Spectra without the Need for Localized Perturbations." Journal of Molecular Spectroscopy 255(1):56-62. Abstract For symmetric top molecules, the normal k = 0, l = 0 and k = 1, l = 1 selection rules for parallel and perpendicular bands, respectively, do not allow the determination of the K-dependent rotational constants, C0 (or A0), D0K, and H0K. However, we show here that several different combinations of allowed and apparently unperturbed rovibrational infrared transitions can give access to those constants. A necessary ingredient for the application of this technique is a band with selection rules k = 1 (or k = 0), l = 2, such as an overtone or difference band, and appropriate other bands. Bands with selection rules k = 2, l = 1 are also useful but are seldom found. As a general rule, more than one vibrational transition is needed. Examples are given for boron trifluoride (BF3), sulfur trioxide (SO3), and cyclopropane (C3H6) for which there are microwave measurements that provide a check on the derived constants. The technique is also extended to a D2d molecule, allene, even though we have no measurements to use as an example. Examples are also given for the determination of dark states from difference bands, and/or hot bands, and also whole forbidden bands that arise from mixing with distant energy levels.
2009. "High-resolution rovibrational study of the Coriolis-coupled nu(12) and nu(15) modes of [1.1.1]propellane." Journal of Molecular Spectroscopy 253(1):41-50. Abstract Infrared spectra of the small strained cage molecule [1.1.1]propellane have been obtained at high resolution (0.0015 cm-1) and the J and K, l rovibrational structure has been resolved for the first time. We recently used combination-differences to obtain ground state parameters for propellane; over 4,100 differences from five fundamental and four combination bands were used in this process. The combination-difference approach eliminated errors due to localized perturbations in the upper state levels of the transitions and gave well-determined ground state parameters. In the current work, these ground state parameters were used in a determination of the upper state parameters for the v12(e′) perpendicular and v15(a2″) parallel bands. Over 4000 infrared transitions were fitted for each band, with J, K values ranging up to 71, 51 and 92, 90 respectively. While the transition frequencies for both bands can be fit nicely using separate analyses for each band, the strong intensity perturbations observed in the weaker v12 band indicated that Coriolis coupling between the two modes was significant and should be included. Due to correlations with other parameters, the Coriolis coupling parameter Zy15z,12x for the v15 and v12 interaction is poorly determined by a transition frequency fit alone. However, by combining the frequency fit with a fit of experimental intensities, a value of -0.42 was obtained, quite close to that predicted from the ab initio calculation (-0.44). This intensity fit also yielded a (dz/dQ15z)/(dx/dQ12x) dipole derivative ratio of 36.5, in reasonable agreement with a value of 29.2 predicted by Gaussian ab initio density functional calculations using a cc-pVTZ basis. This ratio is unusually high due to large charge movement as the novel central Caxial-Caxial bond is displaced along the symmetry axis of the molecule for the v15 mode.
2009. "Absolute integrated intensities of vapor-phase hydrogen peroxide (H202) in the mid-infrared at atmospheric pressure." Analytical and Bioanalytical Chemistry 395(2):377-386. doi:doi:10.1007/s00216-009-2805-x Abstract We report quantitative broadband infrared spectra of vapor-phase hydrogen peroxide (H2O2) with all spectra pressure broadened to atmospheric pressure. The spectra were generated by flowing a concentrated solution (83 weight%) of H2O2 into a gently heated disseminator and diluting with a flow of pure nitrogen carrier gas. The water vapor lines were subtracted from the resulting spectra to yield the spectrum of pure H2O2. Comparison with previous results for the ν6 band strength (including hot bands) compares favorably with the results of Klee et al. [(1999) J. Mol. Spectr. 195, 154] as well as HITRAN. The present results are 433 and 467 cm-2 atm-1 (±8% and ±3% at 298 and 323 K, respectively) for the band strength, matching well the Klee value (S = 467 cm-2 atm-1 at 296 K) for the integrated band. Other bands in the 520-7500 cm-1 interval and their potential for atmospheric monitoring are discussed.
2009. "Passive Standoff Detection of RDX Residues on Metal Surfaces via Infrared Hyperspectral Imaging." Analytical and Bioanalytical Chemistry 395(2):337-348. doi:10.1007/s00216-009 Abstract Hyperspectral images of galvanized steel plates, each containing a stain of RDX, were recorded using a commercial longwave infrared imaging spectrometer. Demonstrations of passive RDX chemical detection at areal dosages between 16 and 90 µg / cm2 were carried out over practical stand-off ranges between 14 and 50 m. Efforts to develop better chemical anomaly and target detection through chemometric analyses are described.
2008. "Low Temperature Measurements of HCN Broadened by N2 in the 14-micron Spectral Region." Journal of Quantitative Spectroscopy and Radiative Transfer 109(6):922-951. doi:10.1016/j.jqsrt.2007.12.017 Abstract N2-broadening and N2-pressure-induced shift coefficients; and the temperature dependence exponent of the N2-broadening and the temperature dependent coefficients of N2-pressure-induced shifts have been measured for transitions in the v2 band of HCN from analysis of high-resolution absorption spectra recorded with two different Fourier transform spectrometers. A total of 34 laboratory spectra recorded at 0.002-0.005 cm-1 resolution and at temperatures ranging from 211 to 300 K were used in the determination of various spectral line parameters. A multispectrum nonlinear least squares curve fitting technique employing a modified Voigt line profile including speed dependence was used in the P- and R-branch measurements. In analyzing the Q branch transitions, the off-diagonal relaxation matrix element coefficients were included in analysis to fit the data. Present results are compared to previous measurements reported in the literature.
2008. "Quantitative Measurement of Integrated Band Intensities of Benzene Vapor in the Mid-Infrared at 278, 298, and 323 K." Journal of Quantitative Spectroscopy and Radiative Transfer 109(15):2511-2522. Abstract Pressure broadened (1 atm. N2) laboratory spectra of benzene vapor (in natural abundance) were recorded at 278, 298, and 323 K, covering 600-6500 cm-1. The spectra were recorded at a resolution of 0.112 cm-1 using a commercial Fourier transform spectrometer. The pressure of each benzene vapor sample was measured using high precision capacitance manometers and a minimum of nine sample pressures were recorded for each temperature. The samples were introduced into a temperature-stabilized static cell (19.94(1) cm pathlength) that was hard-mounted into the spectrometer. From these data a fit composite spectrum was calculated for each temperature. The number density for the three composite spectra was normalized to 296 K. The spectra give the absorption cross section (cm2 molecule-1, naperian units) as a function of wavenumber. From these spectra integrated band intensities (cm molecule-1 and atm-1 cm-2) for intervals corresponding to the stronger benzene bands were calculated and are compared with previously reported values. We discuss and quantify error sources and estimate our systematic (NIST Type-B) errors to be 3% for the stronger bands. The measured absorption coefficients and integrated band intensities are useful for remote sensing applications such as measurements of planetary atmospheres and assessment of the environmental impact of terrestrial oil fire emissions.
2008. "Multispectrum Analysis of the v4 Band of CH3CN: Positions, Intensities, Self and N2 Broadening and Pressure-Induced Shifts." Journal of Quantitative Spectroscopy and Radiative Transfer 109(6):974-994. doi:10.1016/j.jqsrt.2007.11.013 Abstract A multispectrum nonlinear least squares fitting technique has been applied to measure accurate zero-pressure line center positions, Lorentz self- and N2-broadening coefficients and self- and N2-pressure-induced shift coefficients in the parallel ν4 band of CH3CN near 920 cm-1. Fifteen high-resolution (0.0029 cm-1) laboratory absorption spectra of pure and N2-broadened CH3CN recorded at room temperature using the Bruker IFS 125HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington, U.S.A. were analyzed simultaneously. Short spectral intervals containing manifolds of transitions from the same value of J have been fitted together. In all, we have obtained high precision line positions, absolute line intensities, self- and N2-broadening coefficients for P(44) through P(3) and R(0) through R(46) manifolds. All measurements have been fitted successfully assuming a Voigt line shape. Preliminary fits of line intensities up to J = 47 using one principal dipole moment derivative and three Herman-Wallis terms are reported. The results are not fully satisfactory due to perturbations caused by interactions with other bands. The total intensity obtained from this prediction by summing individual line intensities for the v4 band region has been compared with the integrated absorption coefficient reported for the v4 band from lower resolution spectra measured at the same laboratory facility. The variations of N2 broadening, self-broadening, N2- shift and self-shift coefficients with the J and K quantum numbers have been measured for the first time. N2-broadening coefficients decrease with increasing J and K. Some self-broadening coefficients are very large (up to ~2 cm-1 atm-1 at 294 K). Ratios of N2-broadening coefficients to self-broadening coefficients show a compact distribution with rotational quantum number in both the P- and R-branches that range from ~0.45 to 15 with a maxima ratio near J"=13. Pressure-induced shifts for N2 are small (few exceed 0.006 cm-1 atm-1 at 294 K). In contrast, self-shift coefficients are large (maxima of about 0.06 cm-1 atm-1) and are both positive and negative with compact and distributions as a function of rotational quantum number. A calculation of the total internal partition function sum has been performed and those results have been made available for addition to the HITRAN and GEISA databases. We discuss the status of assignments for CH3CN that are currently available for other mid- and far infrared regions
2008. "Assignment, Fit, and Theoretical Discussion of the v10 Band of Acetaldehyde Near 509 cm-1." Journal of Molecular Spectroscopy 252(2):214-229. doi:10.1016/j.jms.2008.09.004 Abstract The lowest small-amplitude vibration in acetaldehyde (CH3CHO) is the in-plane aldehyde scissors mode v10 at 509 cm-1. This mode lies about 175 cm-1 above the top of the barrier to internal rotation of the methyl group and is relatively well separated from other small-amplitude vibrational states (the next fundamental occurring more than 250 cm-1 higher). It thus provides an excellent example of an isolated small-amplitude fundamental (bright state) embedded in a bath of dark states. Since the bath states at these energies are not too dense, and since they arise purely from states of the large-amplitude torsional vibration of the methyl rotor, a detailed spectroscopic analysis of interactions between the bright state and the bath states should be possible. This paper represents the first step toward that goal. We have assigned several thousand transitions in the v10 band (J < 28, K< 12), and have carried out a simultaneous fit of 2400 of these transitions (J < 15, K< 9) with over 8100 transitions to the torsional bath state levels. Three vibration-torsion interactions, which give rise to rather global level shifts of the order of 1 cm-1 in the v10 levels, have been identified and quantitatively fit. A number of vibration-torsion-rotation interactions, which give rise to localized (avoided-crossing) shifts in v10 have also been determined. The present analysis indicates the need for reliable spectroscopic information on more of the torsional bath states in the immediate vicinity of the v10 levels. Possible ways of obtaining such information in future studies are considered.
2008. "High Resolution Infrared Spectroscopy of [1.1.1] Propellane." Journal of Molecular Spectroscopy 248(2):153-160. Abstract The infrared spectrum of [1.1.1]propellane has been recorded at high resolution (0.002 cm-1) with individual rovibrational lines resolved for the first time. This initial report presents the ground state constants for this molecule determined from the analysis of five of the eight infrared-allowed fundamentals v9(e′), v10(e′), v12(e′), v14(a2″), v15(a2″), as well as of several combination bands. In nearly all cases it was found that the upper states of the transitions exhibit some degree of perturbation but, by use of the combination difference method, the assigned frequencies provided over 4000 consistent ground state difference values. Analysis of these gave for the parameters of the ground state the following values, in cm-1: B0 = 0.28755833(14), DJ = 1.1313(5)x10-7, DJK = -1.2633(7)x10-7, HJ = 0.72(4)x10-13, HJK = -2.24(13)x10-13, and HKJ = 2.25(15)x10-13, where the numbers in parentheses indicate twice the uncertainties in the last quoted digit(s) of the parameters. Gaussian ab initio calculations, especially with the computed anharmonic corrections to some of the spectroscopic parameters, assisted in the assignments of the bands and also provided information on the electron distribution in the bridge-head carbon-carbon bond.
2008. "Supersonic Free-jet Quantum Cascade Laser Measurements of v4 for CF3(35)Cl and CF3(37)Cl and FTS Measurements from 400 to 1260 cm-1." Journal of Molecular Spectroscopy 252(1):81-89. doi:10.1016/j.jms.2008.07.001 Abstract A supersonic free-jet spectrum of the 4 band of CF3Cl has been measured using a quantum cascade laser system. Those measurements were combined with a low temperature (-67 C) FTS spectrum of the region 1060 to 1260 cm-1 and with room temperature FTS measurements down to 400 cm-1 to give improved values for the rovibrational constants for the v1, v2, v3, 2v3, 2v5, v4, and v5 states of CF335Cl and CF337Cl. The principal perturbation found by earlier investigators in the v1 band is treated as a very weak Coriolis interaction at several avoided crossings of the rotational levels of the v1 state and the 2v5 state with kl < 0. None of the other vibrational states showed any signs of perturbations. With these new measurements we now have high resolution data on all of the fundamental vibrational states except v6.
2008. "Strategies for Detecting Organic Liquids on Soils Using Mid-Infrared Reflection Spectroscopy ." Environmental Science & Technology 42(15):5700-5705. doi:10.1021/es8005404 Abstract Stand-off monitoring for chemical spills can provide timely information for clean-up efforts and mid-infrared reflection-absorption spectroscopy is one approach being investigated. Anomaly and target detection strategies were examined for detection of four different low-volatility organic liquids on two different soil types. Several preprocessing and signal weighting strategies were studied. Anomaly detection for C−H bands was very good using second derivative preprocessing and provided similar performance to target detection approaches such as generalized least squares (GLS) and partial least squares (PLS) with detections at soil loads of approximately 0.6 to 1.5 mg/cm2. Good performance was also found for detection of P=O, O–H and C=O bands but the optimal strategy varied. The simplicity and generality of anomaly detection is attractive, however target detection provides more capability for classification.
2008. "Detection of Low Volatility Organic Analytes on Soils Using Infrared Reflection Spectroscopy." Journal of Near Infrared Spectroscopy 16(3):179-187. doi:10.1255/jnirs.776 Abstract Previous work on detection of low-volatility liquid organic (and organophosphorus) analytes on soil indicated strong signal in FTIR spectra in the 2966–2855 cm-1 range attributed to C–H vibrational stretching modes. This range is the focus of detection strategies examined here as an anticipated prelude to subsequent detection and classification approaches utilizing additional spectral bands. This laboratory study is being used to test detection algorithms that may be useful for rapid standoff detection of organics compounds on soil. Six signal processing methods (designed to minimize irrelevant variability in the recorded soil reflection-absorption spectra while enhancing signal from analyte compounds possibly present on soil) were studied. These included Savitzky-Golay second derivatives, extended multiplicative scatter correction (EMSC), and a novel alternative to piece-wise EMSC. The preprocessed signal was then used for detection. Previous work utilized principal components analysis (PCA) based multivariate statistical process control methodologies for detection. Six alternative anomaly detection statistics were examined here that were based on the preprocessed signal, weighted signal, and generalized weighted signal. The latter statistic can be considered easier than PCA with many of the same benefits. Two tests corresponding to different monitoring strategies were examined: test data ‘local’ and ‘non-local’ to the calibration data. Although the results are expected to be optimistic, the generalized weighted approach worked extremely well for the ‘local’ detection test, but was less successful for ‘non-local’ test. Results suggest that good characterization of analyte-free soil prior to monitoring will lead to the best detection performance. Second derivative preprocessing showed the best results on receiver operator characteristic curves and it’s ease of application is a distinct advantage. However, it may not be universally successful for all bands to be considered in the future. Both EMSC and the novel ‘piece-wise’ EMSC methodology showed promise, but some improvements may be necessary.
2007. "High Resolution Infrared Study of the 2v9 and v4 Bands of 10BF2OH and 11BF2OH: Evidence of Large Amplitude Effects for the OH- Torsion and OH-Bending Modes in the 9(2) and 4(1) and Excited States." Molecular Physics 105(13-14):1833-1848. doi:10.1080/00268970701426992 Abstract High resolution (2-3x10-3cm-1) Fourier transform infrared spectra of gas phase 10B and 11B enriched and natural samples of BF2OH (difluoroboric acid) were recorded at Wuppertal and Richland. Starting from the results of previous studies [A.Perrin, M.Carvajal-Zaera, Z.Dutkiewicz, J.-M.Flaud, D.Collet, H.Bürger, J.Demaison, F.Willaert, H.Mäder, and N.W.Larsen, Mol. Phys. 102 , 1641 (2004); J. Breidung, J. Demaison, J.-F. D’Eu, L. Margulès, D. Collet, E.B. Mkadmi, A. Perrin and W. Thiel, J. Mol. Spectrosc. 228, 7, (2004)], it was possible to perform the first rovibrational analysis of the 2ν9 (first overtone of ν9, the OH torsion) and ν4 (BOH bending) bands located at about 1043.9 and 961.7 cm-1 and 1042.9 and 961.5 cm-1 for the 10BF2OH and 11BF2OH isotopic species respectively. Numerous “classic” perturbations were observed in the analysis of the 2ν9 and ν4 bands. The energy levels of the 92 bright state are indeed involved in a B- type Coriolis resonance with those of the 6191 dark state. The 41 levels are perturbed by a B-type Coriolis resonance and by an anharmonic resonance with the levels of the 7191 and the 6171 dark states respectively. In addition large amplitude effects were observed for the 2ν9 and also, more surprisingly, the ν4 bands. This results in splittings of the energy levels of about 0.005 and 0.0035 cm-1 for the 92 and 41 states respectively which are easily observable in the P and R branches for both bands. The theoretical model used to reproduce the experimental levels accounts for the classic vibration –rotation resonances. Also the large amplitude torsional (or bending) effects are accounted for within the frame of the IAM (Internal Axis Method) -like approach. The Coriolis resonances between the two torsional (or bending) substates are taken into account by {Jx,Jz} non orthorhombic terms in the v-diagonal blocks. This means that the zquantification axis deviates from the a inertial axis by an axis switching effect of ~35° for the {92,6191} system and of ~16.6° for the {41,7191,6171}) system of interacting vibrational states. The calculation of the relative line intensities for the 2ν9 and ν4 bands accounts for these axis switching effects as well as for the intensity alternation which is due to the nuclear spin statistics since the OH large amplitude torsion and/or bending motion results indeed in an exchange of the two fluorine nuclei.
2007. "The Analysis of Combination and Overtone States of 11BF3 from 1650 to 4600 cm-1." Journal of Molecular Spectroscopy 243(1):16-31. doi:10.1016/j.jms.2007.02.019 Abstract High-resolution (0.0015-0.0035 cm-1) infrared spectra of isotopically enriched 11BF3 have been examined in detail. The analysis of the combination and overtone states within the region of study, from 1650 to 4600 cm-1, led to the assignment of over 25,000 transitions. The major perturbations were due to the Fermi resonances between states possessing one quantum of v4. With corrections through the quadratic rotational terms, the equilibrium Be and Ce values have been determined; 0.3462679 cm -1 and 0.17311506 cm-1, respectively. An improved set of equilibreium rotational constants for 10BF3, consistent with this analysis of 11BF3 are also given. The averaged equilibrium values for both isotopomers lead to a B-F bond distance of re = 130.70 ± 0.0XX pm. All of the quadratic anharmonic constants, with the exception of x33 were independently, experimentally determined. For the first time for BF3, a normal force field analysis was performed that utilized the experimentally determined, fundamental harmonic vibrational frequencies.
2007. "High Resolution Infrared Spectroscopy in the 1200--1300 cm-1 Region and Accurate Theoretical Estimates for the Structure and Ring-Puckering Barrier of Perfluorocyclobutane." Journal of Physical Chemistry A 111(44):11328-11341. doi:10.1021/jp072521f Abstract We present experimental infrared (IR) spectra and theoretical electronic structure results for the geometry, anharmonic vibrational frequencies and accurate estimates of the magnitude and the origin of the ring puckering barrier in C4F8. High-resolution (0.0015 cm-1) spectra of the ν12 and ν13 parallel bands of perfluorocyclobutane (c-C4F8) were recorded for the fist time by expanding a 10% c-C4F8 in helium mixture in a supersonic jet. Both bands are observed to be rotationally resolved in a jet with a rotational temperature of 15 K. The ν12 mode has b2 symmetry under D2d that correlates to a2u symmetry under D4h and consequently has ± ← ± ring puckering selection rules. A rigid rotor fit of the ν12 band yields the origin at 1292.56031(2) cm-1 with B′ = 0.0354137(3) cm-1 and B″ = 0.0354363(3) cm-1. The ν13 mode is of b2 symmetry under D2d that correlates to b2g under D4h and in this case the ring puckering selection rules are ± ! m. Rotational transitions from the ground and first excited torsional states will be separated by the torsional splitting in the ground and excited vibrational states and indeed we observe a splitting of each transition into strong and weak intensity components with a separation of approximately 0.0018 cm-1. The strong and weak sets of transitions were fit separately again using a rigid rotor model to give ν13(strong) = 1240.34858(4) cm-1, B′ = 0.0354192(7) cm-1 and B″ = 0.0354355(7) cm-1 and ν13(weak) = 1240.34674(5) cm-1, B′ = 0.0354188(9) cm-1 and B″ = 0.0354360(7) cm-1. High level electronic structure calculations at the MP2 and CCSD(T) levels of theory with the family of correlation consistent basis sets of quadruple-ζ quality, developed by Dunning and coworkers, yield best estimates for the vibrationally averaged structural parameters r(C-C)=1.568 Å, r(C-F)α=1.340 Å, r(C-F)β=1.329 Å, α(F-C-F)=110.3°, θz(C-C-C)=89.1° and δ(C-C-CC)=14.6° and rotational constants of A=B=0.03543 cm-1, C=0.02898 cm-1, the latter within 0.00001 cm-1 from the experimentally determined values. Anharmonic vibrational frequencies computed using higher energy derivatives at the MP2 level of theory are all within < 27 cm-1 (in most cases < 5 cm-1) from the experimentally measured fundamentals. Our best estimate for the ring puckering barrier at the CCSD(T)/CBS (Complete Basis Set) limit is 132 cm-1. Analysis of the C4F8 electron density suggests that the puckering barrier arises principally from the σCC→σCF * hyperconjugative interactions that are more strongly stabilizing in the puckered than in the planar form. These interactions are, however, somewhat weaker in C4F8 than in C4H8, a fact that is consistent with the smaller barrier in the former (132 cm-1) with respect to the latter (498 cm-1). Acknowledgements: Part of this work was performed in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC06-76RLO 1830 with Battelle Memorial Institute, which operates the Pacific Northwest National Laboratory. The EMSL is a national user facility funded by the Office of Biological and Environmental Research in the U.S. Department of Energy. Computer resources were provided by the Division of Chemical Sciences, US Department of Energy. EDG acknowledges the Indiana State University Office of Information Technology for the use of their computer resources.
2006. "Structure, Vibrational Spectra and Ring Puckering Barrier of Cyclobutane." Journal of Physical Chemistry A 110:10487-10494. doi:10.1021/jp062472r Abstract We present the results of high level ab initio calculations on the structure and puckering barrier of cyclobutane in an effort to establish the minimum theoretical requirements needed for their accurate description. Our best computed value for the puckering angle is 29.68o. Furthermore we found that accurate estimates for the barrier between the minimum (D2d) and transition state (D4h) configurations require both higher levels of electron correlation [MP4, CCSD(T)] and basis sets of quadruple-z quality or larger. By performing CCSD(T) calculations with basis sets as large as cc-pV5Z we obtained a complete basis set (CBS) estimate of 498 cm-1 for the puckering barrier. Our estimate for the barrier is within 10 cm-1 to the value proposed originally, but it lies ~50 cm-1 higher than the one obtained more recently, therefore revisiting the analysis of the experimental data might be warranted. The results of the current study can serve as a guide for calculations on the substituted four member ring compounds. To this end we present a method for estimating the barrier height at higher levels of electron correlation [MP4, CCSD(T)] from the MP2 results.
2006. "Observation of a Forbidden E"-A' (1) Infrared Transition in (BF3)-B-11." Journal of Molecular Spectroscopy 238(2):135-144. Abstract The forbidden 011100-000000 E"-A1' transition of 11BF3 has been observed in absorption in the infrared near 2140 cm-1. Although weak, the entire band is observed and does not show any sign of intensity borrowing from nearby bands. The transitions obey the electric dipole allowed selection rules k = +2, l = +1. As shown by the J and K dependence of the line intensities, the band appears to derive its intensity from terms in the dipole moment operator described by Aliev and Watson [1]. That theory is further developed and it is shown that, for this particular case, the intensity comes largely from the term in the dipole moment operator that governs the intensity of the 002200-000000 transitions and to a lesser extent from terms that govern the intensity of the 001111-000000 transitions and the fundamental bands.
2006. "High Resolution studies of Tropolone in the So and S1 Electronic States: Isotope Driven Dynamics in the Zero-Point Energy Levels." Journal of Chemical Physics 124(7):074309. doi:10.1063/1.2165652 Abstract Rotationally resolved microwave (MW) and ultraviolet (UV) spectra of jet-cooled tropolone have been obtained in S0 and S1 electronic states using Fourier-transform microwave and UV laser/molecular beam spectrometers. In the ground electronic state, the MW spectra of all heavy atom isotopomers including one 18O and four 13C isotopomers were observed in natural abundance. The OD isotopomer was obtained from isotopically enriched samples. The two lowest tunneling states of each isotopomer except 18O have been assigned. For the asymmetric 13C structures, the magnitudes of tunneling-rotation interactions diminished with decreasing distance between the heavy atom and the tunneling proton. In the limit of closest approach, the v=0 state of 18O was well-fit to asymmetric rotor Hamiltonians, signifying a drastic change in the tautomerization dynamics. Comparisons of the substituted atom coordinates with theoretical predictions at the MP2/aug-cc-pVTZ level of theory suggest the localized v=0 and v=1 wavefunctions of the heavier isotopes favor the C-OH and C=O forms of tropolone, respectively. The only exception occurs for 13C-OH and 13C=O structures which correlate to the v=1 and v=0 states, respectively. These preferences reflect kinetic isotope effects as quantitatively verified by the calculated zero point energy differences (ΔZPE's) between members of the asymmetric atom pairs. The ΔZPE's are principally defined by contributions from the out-of-plane zero-point motions and aid in elucidating the mode-specific nature of the tunneling splittings. From rotationally resolved data of the 0+-0+/0+-0- and 0--0-/0--0+ bands in S1, lineshape fits have yielded different Lorentzian linewidths, increasing from 131.1(8) MHz to 143.3(8) MHz, respectively. This 12.2(8) MHz increase over the 18.04(2) cm-1 tunneling splitting interval in S1 correlates with a nearly monotonic increase in the intersystem crossing rate when extrapolated to higher vibrational excess energies in S1, suggesting a dependence of the non-radiative decay dynamics on tunneling state.
2006. "Multivariate Curve Resolution Applied to Infrared Reflection Measurements of Soil Contaminated with an Organophosphorus Analyte." Applied Spectroscopy 60(7):713-722. doi:10.1366/000370206777887026 Abstract Multivariate curve resolution (MCR) is a powerful technique for extracting chemical information from measured spectra on complex mixtures. The difficulty with applying MCR to soil reflectance measurements is that light scattering artifacts can contribute much more variance to the measurements than the analyte(s) of interest. Two methods were integrated into a MCR decomposition to account for light scattering effects. Firstly, an extended mixture model using pure analyte spectra augmented with scattering ‘spectra’ was used for the measured spectra. And secondly, second derivative preprocessed spectra, which have higher selectivity than the unprocessed spectra, were included in a second block as a part of the decomposition. The conventional alternating least squares (ALS) algorithm was modified to simultaneously decompose the measured and second derivative spectra in a two-block decomposition. Equality constraints were also included to incorporate information about sampling conditions. The result was an MCR decomposition that provided interpretable spectra from soil reflectance measurements.
2005. "18O Effects on the Infrared Spectrum and Skeletal Tunneling of Tropolone." Journal of Chemical Physics 122:224311. Abstract Infrared absorption profiles observed for vibrational transitions of gaseous tropolone often show sharp Q branch peaks, some of them ultra-narrow spikes, indicative of the band origins for vibrational state-specific spectral tunneling doublets. In this work oxygen isotope effects for two CH wagging fundamentals, the COH torsion fundamental, and the skeletal contortion fundamental are reported. They allow considerations to be given: (1) oxygen isotope effects on the vibrational frequencies and state-specific tunneling splittings; (2) the asymmetry offset of the potential energy minima for 16O, 18O-tropolone; and (3) additional details concerning previously proposed high J rotation-contortion fundamental. The new results help to characterize the skeletal contortion fundamental and support the jo9nt participation of skeletal tunneling with H tunneling in the vibrational state-specific tautomerization processes of tropolone in its ground electronic state.
2005. "The High-Resolution Infrared Spectrum of 11BF3 From 400 to 1650 cm-1." Journal of Molecular Spectroscopy 234(1):122-136. Abstract High-resolution infrared spectra of boron trifluoride, enriched to 99.5 atom % 11B, have been measured from 400 cm-1 to 1650 cm-1. In that region we have identified and analyzed 16 absorption bands attributed to the three fundamental bands, two combination bands, ten hot bands and one difference band. All possible states were accessed in this region through direct transitions either from the ground state or as hot bands from thermally populated levels. The spectral resolution of the measurements varied from 0.0015 cm-1 to 0.0020 cm-1. An improved set of ground state rotational constants and rovibrational constants for the infrared active fundamental vibrations have been determined from over 31,000 assigned transitions. This study resulted in the first direct characterization of the infrared inactive v1 state of 11BF3 leading to values for v1, v1B and v1C of 885.843 221(22), 0.000 505 242(26) and 0.000 678 567(55) cm-1, respectively. The Fermi resonance perturbation between the Ev3 states v3 and 3v4 (l=+1) was further elucidated by observation of hot band transitions to both the 3v4(l=+1)and 3v4(l=v3) states. Several other resonances were also found including the weak rotational interaction, between the A1v state 2v2 and the E' state of v1+v4.
2005. "The High-Resolution Infrared Spectrum of 10BF3 from 400 to 4600 cm-1." Journal of Molecular Structure 742:3-20. doi:10.1016/j.molstruc.2004.11.089 Abstract High-resolution infrared spectra of boron trifluoride, enriched to 99.5 atom % 10B, have been measured from 400 cm-1. In that region we have identified and analyzed 17 absorption bands including three fundamentals. In addition, 3 hot bands associated with v2 were analyzed, 7 hot bands associated with v4, two with v1+v4 and one hot band each associated with the v3 and v1+v2 bands. The spectral resolution of the measurements varied from 0.0015 cm -1 at the lowest wavenumber to 0.0035 cm -1 at the highest wavenumber. This study resulted in the first direct characterization of the v1 state via two routes, one through the combined analysis of the 110000-000000 and 110000-100000 vibrational transitions and the other through the analysis of the 001100-000000 and 001100-100000 transitions. All of the quadratic vibrational anharmonic constants have been determined except x23. An improved set of ground state rotational constants has been determined for 10BF3. With corrections through most but not all of the quadratic rotational terms we have found that Be=0.346170 ± 0.000003 cm-1 and Ce = 0.173038 ± 0.000006 cm-1. These give a B-F bond distance of re = 130.731 ± 0.010 pm. The effects of l-type resonance were used to locate certain vibrational states that could not be directly observed through infrared transitions from the ground state. The splitting of the A1´ and A2´ components of v3+v4 was found to be quite large, 6.131 ± 0.007 cm-1. Several other resonances were also found including the weak vibrational interaction, which had been overlooked by earlier workers, between 2v2 and the A1´ vabrational state 3v4.
2005. "Application of Extended Inverse Scatter Correction to Mid-Infrared Reflectance Spectra of Soil." Journal of Chemometrics 19(5-7):271-281. doi:10.1002/cem.929 Abstract Scattering artifacts adversely affect infrared reflectance measurements of powders and soils, and extended inverse scatter correction (EISC) is a flexible method useful for correcting for these artifacts. EISC was used to correct mid-infrared reflectance spectra of two different soils coated with dibutyl phosphate and the results were examined using regression analysis. To determine the correction, EISC fits a measured spectrum to a reference spectrum. However, if measured spectra contain features not included in the reference spectrum the fit can be biased resulting in poor correction. Weighted and robust least squares were used to account for these potential biases. Additionally, the present work demonstrates how analyte-free samples can be used to determine basis functions for an extended mixture model used in the correction. Corrected spectra resulted in partial least squares models that performed at least as well as 2nd derivative spectra and were more interpretable.
2004. "Analysis of High-Resolution Infrared and CARS Spectra of ³⁴S¹⁸O₃." Journal of Molecular Spectroscopy 227(1):50-59. Abstract As part of a series of investigations of isotopic forms of sulfur trioxide, high-resolution infrared and coherent anti-Stokes Raman spectroscopies were used to study the fundamental modes and several hot bands of 32S18O3. Hot bands originating from the v2 and v4 bending mode levels have been found to couple strongly to the IR-inactive v1 symmetric stretching mode through indirect Coriolis interactions and Fermi resonances. Coriolis coupling effects are particularly noticeable in 32S18O3 due to the close proximity of the v2 and v4 fundamental vibrations, whose deperturbed wavenumber values are 486.488 13(4) and 504.284 77(4) cm-1. The uncertainties in the last digits are shown in parentheses and are two standard deviations. From the infrared transitions, accurate rovibrational constants are deduced for all of the mixed states, leading to deperturbed values for v1, and of 1004.68(2), 0.000 713(2), and 0.000 348(2) cm-1, respectively. The Be value is found to be 0.310 820(2) cm-1, yielding an equilibrium bond length re of 141.7333(4) pm that is, within experimental error, identical to the value of 141.7339(3) pm reported previously for 34S18O3. With this work, precise and accurate spectroscopic constants have now been determined in a systematic and consistent manner for all the fundamental vibrational modes of the sulfur trioxide D3h isotopomeric forms 32S16O3, 34S16O3, 32S18O3, and 34S18O3.
2004. "Analysis of High-Resolution Infrared and CARS Spectra of ³⁴S¹⁸O₃." Journal of Molecular Spectroscopy 223(2004):84-95. Abstract Three fundamental modes and several hot bands of 34S18O3 have been investigated using both infrared spectroscopy and coherent anti-Stokes Raman scattering spectroscopy (CARS). Coriolis coupling effects are particularly noticeable in 34S18O3 due to the close proximity of the v2 and v4 fundamental vibrations, whose wavenumber values are 477.508 64(5) and 502.055 65(4) cm-1. The uncertainties in the last digits are shown in parentheses and are two standard deviations. Hot band transitions from v2, v4 levels give access to infrared inactive v2, v4 combination/overtone levels which interact strongly with levels of the Raman-active v1 symmetric stretching mode due to indirect Coriolis couplings, l-resonances, and Fermi resonances. The result is a complex v1 CARS Q- branch spectrum that is the most perturbed of the four SO3 isotopomers we have studied. The relative importance of these interaction terms on the v1 CARS spectrum is examined in some detail and accurate rovibrational constants are determined for all of the mixed states, leading to deperturbed values of 1004.662(24), 0.000 350 3(9), and 0.000 706 6(12) cm-1 for v1, α1B, and α1C, respectively. The B e value is found to be 0.310 817(12) cm-1, which gives an equilibrium bond length re of 141.7339(3) pm, in excellent agreement with values of 141.7340(1) and 141.7347(7) pm reported earlier for 32S16O3 and 34S16O3.
2004. "Analysis of Some Combination-Overtone Infrared Bands of (SO3)-S-32-O-16." Journal of Molecular Spectroscopy 225(2):109-122. Abstract Several new bands for 32S16O3 have been measured and analyzed. The principal bands observed were v1+v2 (at 1561 cm-1), v1+v4 (at 1594 cm -1) v3+ v4 (at 1918 cm-1), and 3v3 (at 4136 cm-1). Except for 3v3, these bands are very complicated because of (a) the Coriolis coupling between v2 and v4 (b) the Fermi resonance between v1 and 2v4, (c) the Fermi resonance between v1 and 2v2, (d) ordinary l-type resonance that couples levels that differ by 2 in both the k and l quantum numbers, and (e) the vibrational l-type resonance between the A1 and A2 levels of v3+v4. The unraveling of the complex pattern of these bands was facilitated by a systematic approach to the understanding of the various interactions. Fortunately, previous work on the fundamentals permitted good estimates of many constants necessary to begin the assignments and the fit of the measurements. In addition, the use of hot band transitions accompanying the v3 band was an essential aid in fitting the v3+v4 transitions since these could be directly observed for only one of four interacting states. From the hot band analysis we find that the A1 vibrational level is 3.50cm-1 above the A2 level, i.e., r34=1.75236(7) cm-1.
2004. "Rotationally Resolved Spectroscopy of the nu(8) Band of cis-Methyl Nitrite." Journal of Molecular Spectroscopy 225(2):182-188. Abstract The 770-880 cm-1 region of the methyl nitrite spectrum has been recorded at a resolution of 0.0015 cm-1 in a static cell. Consistent with published determinations of the barrier to internal rotation of the methyl group, bands belonging to the trans isomer are very congested while those belonging to the cis isomer are more tractable.
2004. "Air-Broadening Parameters in the ν3 Band of 14N16O2 Using a Multispectrum Fitting Technique." Journal of Molecular Spectroscopy 228(2):593-619. Abstract Air-broadened line widths, pressure-induced shift coefficients and their temperature dependences were retrieved for over 1000 transitions in the v3 band of 14N16O2 at 6 μm. In addition, precise line center positions and relative intensities were also determined. The results were obtained by fitting simultaneously 27 spectra recorded at high resolution (0.002 cm-1 to 0.006 cm-1) with two Fourier transform spectrometers and gas sample temperatures ranging from 206 K to 298 K. It was necessary to modify the multispectrum fitting software to accommodate constraints on the retrieved parameters of closely-spaced spin-split doublets in order to successfully determine their broadening and shift parameters. The variations of the widths, shifts and their temperature dependences on the quantum numbers were investigated. Subsets of the observed line widths were reproduced to within 3% using an exponential smoothing function.
2003. "The v(2) and 2 v3 Bands of (SO3)-S-32-O-16, (SO3)-S-32-O-18, (SO3)-S-34-O-16 and (SO3)-S-34-O-18." Journal of Molecular Spectroscopy 222(2):142-152. Abstract The fifth of a series of publications on the high resolution rotation-vibration spectra of sulfur trioxide reports the results of a systematic study of the v3(é) and 2v3(A1�+E�) infrared bands of the four symmetric top isotopomers 32S16O3, 34S16O3, 32S18O3, and 34S18O3. An internal coupling between the l = 0 and l = +2 levels of the 2v3 (A1�+E�) states was observed. This small perturbation results in a level crossing between K-l = 9 and 12, in consequence of which the band origins of the A1�, l=0 “ghost” states could be determined to a high degree of accuracy. Ground and upper state rotational as well as vibrational anharmonicity constants are reported. The constants for the center-of-mass substituted species 32S16O3 and 34S16O3 vary only slightly, as do the constants for the 32S18O3, 34S18O3 pair. The S-O bond lengths for the vibrational ground states of the species 32S16O3, 34S16O3, 32S18O3 and 34S18O3, are, respectively, 141.981992(6), 141.979412(20), 150.605240(73), and 150.602348(73) pm, where the uncertainties, given in parentheses, are two standard deviations and refer to the last digits of the associated quantity.
2003. "NH3 and PH3 Line Parameters: The 2000 HITRAN Update and New Results." Journal of Quantitative Spectroscopy and Radiative Transfer 82(1-4):293-312. Abstract This paper describes the improvements incorporated into the 2000 version of the HITRAN database for ammonia (NH3), as well as newer results for phosphine (PH3) not included in HITRAN 2000.
2003. "Anhydrous Nitric Acid Integrated Absorption Cross Sections: 820 - 5300 cm-1." Journal of Quantitative Spectroscopy and Radiative Transfer 82(1-4):p. 429-441. Abstract Fourier transform infrared absorbance measurements of small aliquots of anhydrous nitric acid were used to determine regional, integrated cross-sections at 278.2K, 298.22K and 323.15K. Spectra were recorded with pressure broadened samples (1 atmosphere nitrogen), in a 20 cm path length cell at a spectral resolution of 0.112 cm-1. Spectral regions measured included the vibrational bands: v1 (~3575 cm-1), v2 (~1710 cm-1), v3, v4 (~1335 cm-1), and v5, 2v9 (~890 cm-1) and regions of weaker absorption between 820 cm-1 and 5300 cm-1. We observed expected changes in the distribution of rovibrational intensities with temperature, but to the accuracy of our measurements, cross-sections integrated over entire vibrational bands are independent of temperature.
2003. "High Resolution Infrared Studies of the v2, v4 Bands of 34S16O3, Including Both Intensity and Wavenumber Perturbations." Journal of Molecular Spectroscopy 218(2):197-203. Abstract The infrared spectrum of the v2, v4 bending mode region of 34S-substituted sulfur trioxide, 34S16O3, has been recorded at a resolution of 0.0025 cm-1. The v2 and v4 levels are coupled by a Coriolis interaction, yielding significant spectral shifts that have been successfully analyzed to obtain rovibrational constants for the ground state and both fundamentals. Comparisons are made with 32S16O3 parameters and the Bo rotational constant is found to be 0.348 556 04(28) cm-1, only very slightly larger than the corresponding value of 0.348 543 33(5) cm-1 for 32S16O3. Coriolis and l-type resonance interactions between the v2 and v4 levels produce frequency shifts and strong intensity perturbations in the spectra that are considered for both 34S16O3 and 32S16O3. The resulting analysis yields an average value of +0.62(8) for the dipole derivative ratio (∂μx/∂Q4x) (∂μz/∂Q2) and a positive sign for the product of this ratio with the ζy2,4 Coriolis constant, for which experiment gives +0.5940(15). Ab initio calculations indicate that the signs of ∂μx/∂Q4x and ∂μz/∂Q2 are both positive and hence ζy2,4 is also positive, in agreement with earlier calculations. These signs indicate that the effective charge movement in the xz plane has the same sense of rotation as Q2, Q4x atom motion in this plane that produces a py vibrational angular momentum component, correlated motion that is confirmed by ab initio calculations.
2003. "Analysis of the v2, v4 Infrared Hot Bands and v1 CARS Spectrum of 34S16O3." Journal of Molecular Spectroscopy 218(2):204-212. Abstract High-resolution (0.0015 cm-1) infrared spectroscopy has been used to study the 34S16O3 IR-active hot bands originating from the v2 and v4 bending mode levels and terminating in the states 2v2 (l=0), v2+v4 (l=+1), and 2v4 (1=0, +2). The upper states are strongly coupled via Fermi resonance and indirect Coriolis interactions to the v1 symmetric stretching mode levels that are only directly accessible from the ground state via a Raman-active transition. A Coherent anit-Stokes Raman (CARS) spectrum of v1 for 34S16O3 is presented which is dramatically different from the corresponding one for 32S16O3. From the infrared transitions, accurate rovibrational constants are deduced for all the mixed states, leading to deperturbed values for v1, α1B, and α1C of 1064.920(84), 0.000 834 5 (54), and 0.000 410(11) cm-1 respectively. The uncertainties in the last digits are shown in parentheses and represent two standard deviations. These parameters reproduce the unresolved Q-branch contour of the CARS spectrum very well. Various other rotational and vibrational parameters have been determined, leading to values of Be = 0.349 760 6(33) cm-1 and re = 141.734 70(68) pm, values that are identical (within experimental error) to those found for 32S16O3.
2002. "Removing Aperture-Induced Artifacts from Fourier Transform Infrared Intensity Values." Applied Optics 41(15):2831-2839. Abstract Two FTIR intensity artifacts have been observed at moderately high (0.1 cm-1) spectral resolution, 1) light reflected off the aperture back was double modulated by the interferometer productin a 2f alias and 2) the warm (~310 K) annulus of the aperture seen by a cooled detector resulted in both distorted line shapes and anomalous intensities in the fingerprint region. Although the second artifact has been alluded to before, we report corrections to remove both anomalies and demonstrate the efficacy of these corrections. Prior to correction, integrated band intensities were found to be in error by up to 12%. Presumably all medium resolution (<0.5cm-1) optical-flat mid-IR spectrometers suffer from these artifacts.
2002. "Analysis of v2, v4 Infrared Hot Bands of 32S16O3: Resolution of the Puzzle of the v1 CARS Spectrum." Journal of Molecular Spectroscopy 216:105-112. Abstract Further analysis of the high-resolution (0.0015 cm-1) infrared spectrum of 32S16 O3 has led to the assignment of more than 3,100 hot band transitions from v2 and v4 levels to the states 2v2 (l=0), v2+v4 (l=1), and 2v4 (l=0, 2). These leve ls are strongly coupled via Fermi resonance and indirect Coriolis interactions t o the v1 levels which are IR-inaccessible from the ground state. The unraveling of these interactions has allowed for the solution of the unusual and complicat ed structure of the v1 CARS spectrum. This has been accomplished by locating ov er 400 hot-band transitions to levels that contain at least 10% v1 character. T he complex CARS spectrum results from a large number of avoided energy level cro ssings between these states. Accurate rovibrational constants are deduced for a ll the mixed states for the first time, leading to deperturbed values of 1064.924(11), 0.000 840 93(64), and 0.000 418 19(58) cm-1 for v1, a1B, and a1C, respect ively. The uncertainties in the last digits are shown in parentheses and repres ent two standard deviations. In addition, new values for some of the anharmonic ity constants have been obtained. Highly accurate values for the equilibrium ro tational constants Be and Ce are deduced, yielding independent, nearly identical determinations of the SO re bond length of 141.734 03(9) and 141.732 54(13) pm, respectively.
2002. "Analysis of nu(2), nu(4) infarared Hot Bands of (SO3)-S-32-O-16: Resolution of the Puzzle of the nu(1) CARS Spectrum." Journal of Molecular Spectroscopy 216(1):105-112. Abstract Further analysis of the high-resolution (0.0015 cm(-1) infrared spectrum of S-32(16) 03 has led to the assignment of more than 3100 hot band transitions from the nu(2) and nu(4) levels to the states 2nu(2) (1=0), nu(2) + nu(4) (1=+/-1), and 2nu(4) (1=0, +/-2).
2001. "High Resolution Infrared Spectra of the v2, v3, v4 and 2v3 Bands of 32S16O3." Journal of Molecular Spectroscopy 210:240-249. Abstract New measurements are reported for the infrared spectrum of sulfur trioxide, 32S16O3, with resolutions ranging from 0.0015 cm-1 to 0.0025 cm-1. New rovibrational constants have been measured for the fundamentals v2, v3, and v4, and the overtone band 2v3. Comparisons are made with the earlier high resolution measurements on SO3 and the high correlation among some of the constants related to the Coriolis coupling of the v2 and v4 levels is duscussed in order to understand the areas of disagreement with the arlier work. Splittings of some of the levels are observed and hte splitting constant for K = 3 of the ground state is determined for the first time. Other observed splittings include the K = 1 levels of 2v3 (I = 2), the K = 2 levels of the v3 and v4 states and the K = 3 levels of v2. This analysis shows that there are level corssings between the I = 0 and I = 2 states of 2v3 that allow one to determine the separation of the sub-band centers for those two states even thoug the I = o state is a dark state. This is a generalized phenomenon that should be found for many other molecules with the same symmetry. The I-type resonance constant that couples the I = 0 and 2 states is roughly the same as q3 which causes the splitting of the I = 1 levels of the v3 fundamental.
2001. "Coherent Raman and Infrared Studies of Sulfur Trioxide." Journal of Molecular Spectroscopy 210:233-239. Abstract High resolution (0.001 cm-1) coherent anti-Stokes Raman scattering (CARS) was used to observe the Q-branch structure of the IR-inactive n1 symmetric stretching mode of 32S 16O3 and its various 18O isotopomers. The v1 spectrum of 32S 16O3 reveals two intense Q-branch regions in the 1065-1067 cm-1 region, with surprisingly complex vibrational-rotational structure not resolved in earlier studies. Efforts to simulate this with a simple Fermi-resonance model involving v1 and 2v4 do not reproduce the spectral detail nor yield reasonable spectroscopic parameters. A more subtle combination of Fermi resonance and indirect Coriolis interactions with nearby states; 2v4 (l = 0, ? 2), v2+v4 (l = ? 1), 2v2 (l =0) is suspected and a determination of the location of these coupled states by high resolution infrared measurements is underway. At medium resolution (0.125 cm-1), the infrared spectra reveal Q-branch features from which approximate band origins are estimated for the v2, v3, v4 fundamental modes of 32S 18O3, 32S 18O2 16O and 32S 18O 16O2. These and literature data for 32S 16O3 are used to calculate force constants for SO3 and a comparison is made with similar values for SO2 and SO. The frequencies and force constants are in excellent agreement with a recent ab initio calculation by Martin. *In memory of Dr. Nicolae Vulpanovici (1968-2001)
2000. "High-Resolution Infrared Spectrum of the Ring-Puckering Band, nu(10), of Diborane." Journal of Molecular Spectroscopy 201(2):285-291. Abstract The spectrum of the nu10 band of diborane, arising from the ring puckering vibration, has been obtained with a spectral resolution of 0.0015 cm-1 in the region 275 to 400 cm-1. The spectrum of a sample enriched in 10B was recorded as well as one with naturally abundunt boron, i.e., 64% 11B2H6, 32% 10BH6 and 4% 10B2H6. This mode is the lowest vibrational level of the molecule and is unperturbed, allowing a complete assignment of not only the fundamental bands but also the 2v10 - v10 hot bands of all three boron isotopomers. The intensities of several hundred lines of the fundamental and hot bands of all isotopomers have been measured and vibrational transitition moments have been obtained. Finally, it has been shown that the harmonic approximation does not apply for v10.
2000. "Rotationally Resolved Spectroscopy of a Librational Fundamental Band of Hydrogen Fluoride Tetramer." Journal of Chemical Physics 113(2):707-718. Abstract The rotationally resolved spectrum of a fundamental band of hydrogen fluoride tetramer has been recorded using a pulsed, slit jet diode laser spectrometer. The band has a parallel rotational structure and is assigned as the H-F out-of-plane libration fundamental with Au symmetry. Ninety-five ground state combination differences were fit to a symmetric top Hamiltonian to give the following ground state rotational constants: B" = 0.132081(7) cm-1, DJ" = 7.1(7) X 10-7 cm-1, DJK" = -9(2) X 10-7 cm-1, HJJJ" = 6(2) X 10-10 cm-1, HJJK" = 9(7) X 10-10 cm-1, HJKK" = -1.3(8) X 10-10 cm-1. A total of 190 transitions were fit to determine the upper state spectroscopic constants: v4 = 714.7849(1) cm-1, B' = 0.129634(5) cm-1, [delta](C ? B) = 0.001344 cm-1, DJ' = 6.4(5) X 10-7 cm-1, DJK' = -4.5(6) X 10-7 cm-1, [delta]DK = 2.92(8) X 10-6 cm-1, HJJJ' = 3(1) X 10-10 cm-1, HJJK' = 9(7) X 10-10 cm-1, HJKK' = -1.55(6) X 10-8 cm-1, [delta]HKKK'= -4.65(6) X 10-8 cm-1. Furthermore, a perpendicular band of Eu symmetry centered at 752.7 cm-1 has been assigned as the H-F in-plane libration fundamental of the HF tetramer. Finally a parallel band has also been observed at 741.0 cm-1 with B" = 0.076 cm-1 and has been assigned as the A" symmetry, H-F out-of-plane libration fundamental of HF pentamer. Also, structural parameters and harmonic vibrational frequencies are estimated from high-level, first principles calculations for this system.
1999. "Direct Absorption Spectroscopy of Water Clusters." Journal of Physical Chemistry A 103(43):8620-8624. Abstract Fourier Transform infrared spectrometry has been used to study the vibrational spectroscopy of water clusters...
1998. "High Resolution Infrared Study of the nu(14), nu(17) and nu(18) bands of (B2H6)-B-11 and (BBH6)-B-10-B-11." Journal of Molecular Spectroscopy 191(2):331-342. Abstract ABSTRACT: Using high resolution Fourier transform spectra, a thorough analysis of the nu14 c-type, nu17 a-type and nu18 a-type bands of both 11B2H6 and 10B11BH6 has been carried in the 10.3, 6.2 and 8.5 um spectral regions, respectively. From this analysis is a large set of precise ground state combination differences with J values up to 36 (31) and Ka values extending to 18 (18) was derived for 11B2H6(10B11BH6). These data were fitted using a Watson-type Hamiltonian leading to accurate ground state rotational constants. An rs value for the B--B distance has been determined to be 1.7645(10) A. The determination of upper state levels of each of the bands are strongly perturbed by nearby dark states. To account for these strong localized resonances, it was necessary to introduce the relevant interacting terms in the Hamiltonian matrix. As a result it was possible to calculate the upper state energy levels quite satisfactorily. From these fits, estimates of the band centers and a few of the rotational constants of the resonating dark states were obtained.