EMSL: Tom Blake's Publications

Blake TA, JF Kelly, NB Gallagher, PL Gassman, and TJ Johnson. 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.

Johnson TJ, RL Sams, SD Burton, and TA Blake. 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.

Kirkpatrick RW, T Masiello, N Jariyasopit, JW Nibler, AG Maki, TA Blake, and A Weber. 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.

Maki A, T Masiello, TA Blake, JW Nibler, and A Weber. 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.

Masiello T, A Maki, and TA Blake. 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.

Gallagher NB, PL Gassman, and TA Blake. 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.

Gallagher NB, PL Gassman, and TA Blake. 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.

Kelly JF, A Maki, TA Blake, and RL Sams. 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.

Kirkpatrick RW, T Masiello, N Jariyasopit, A Weber, JW Nibler, A Maki, TA Blake, and TL Hubler. 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.

Kleiner I, N Moazzen-Ahmadi, ARW McKellar, TA Blake, RL Sams, SW Sharpe, G Moruzzi, and JT Hougen. 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.