Scientific Publications 2001
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. "Time-Dependent Density Functional Theory Calculations of Photoabsorption Spectra in the Vacuum Ultraviolet Region." Journal of Physical Chemistry A 105(20):4953-4962. Abstract Time-dependent density functional theory (TD-DFT) calculations of transition energy and oscillator strength of formaldehyde, benzene, ethylene and methane molecules are performed. It was found that the LDFT transition energies tend to be smaller than experimental values by 0.1 - 1.3 eV. Inclusion of nonlocal effects made the calculated energies to be larger than the LDFT (local density functional theory) values and thus made the energies to be closer to the experimental values for the case of formaldehyde, ethylene and methane molecules. For benzene, no significant change in the calculated transition energies induced by the addition of nonlocal effects was observed. For the oscillator strength, it was found that a drastic improvement in the accuracy for the prediction from that at the CIS (configuration interaction singles) level can be achieved with the TD-DFT method. The agreement between our TD-DFT values and experimental values were excellent both at the LDFT and NLDFT (nonlocal density functional theory) level with the latter being slightly more close to experimental values than the former.
2001. "Computational Dosimetry for Electron Microbeams: Monte-Carlo Track Simulation with Confocal Microscopy." Radiation Research 156(4):438-439. Abstract Both in vitro and in vivo experiments show that cells that do not receive energy directly from the radiation field (bystanders) respond to radiation exposure. This effect is most easily demonstrated with radiation fields composed of particles with high linear energy transfer (LET) that traverse only a few cells before they are stopped. Even at a moderate fluence of high-LET radiation only a small fraction of cells in the irradiated population are hit; hence, many bystanders are present. Low-LET radiation tends to generate a homogenous distribution of dose at the cellular level so that identifying bystanders is much more difficult than in experiments with the same fluence of high-LET radiation. Experiments are underway at several laboratories to characterize bystander responses induced by low-LET radiation. At the Pacific Northwest National Laboratory, experiments of this type are being carried out with an electron microbeam. A cell selected to receive energy directly from the irradiation source is placed over a hole in a mask that covers an electron gun. Monte Carlo simulations by Miller et al.1) suggest that individual mammalian cells in a confluent monolayer could be targeted for irradiation by 25 to 100 keV electrons with minimal dose leakage to their neighbors. These calculations were based on a simple model of the cellular monolayer in which cells were assumed to be cylindrically symmetric with concentric cytoplasm and nucleus. Radial profiles, the lateral extent of cytoplasm and nucleus as a function of depth into a cell, were obtained from confocal microscopy of HeLa-cell monolayers.