Search

We present two simple models for calculating photoabsorption spectra of bent symmetric triatomic molecules, one designed for light-heavy-light systems with an inactive bending mode and a more general one with no assumptions about atomic mass ratios and where bending motion may be active. Both models are extensions of an earlier model [R. T Pack, J. Chem. Phys. 65, 4765 (1976)] for the photodissociation of collinear symmetric triatomic molecules which showed that excitation to a single dissociative electronic state can give absorption spectra with rich structure due to bound degrees of freedom perpendicular to the dissociation coordinate. Similarly, the present models predict structure in the absorption spectra which is easily understood in terms of the vibrational frequencies and bond lengths, and the steepness and height of the excited state barrier. As a test case, we use the models to calculate the photoabsorption spectra of the X 1A1→A 1B1 transition in water which is known to involve a single dissociative excited state surface. We find that these models, which only require knowledge of the ground-state potential-energy surface near the minimum and the excited state potential-energy surface in the barrier region, are quite successful and may serve as simple tools to investigate photoabsorption spectra of other molecules. [ABSTRACT FROM AUTHOR]

Measurements of the rise and decay times, relative intensities, and pressure dependence of the 1.0, 1.9, and 2.3 μm laser-induced fluorescence (LIF) of plutonium hexafluoride (PuF6) excited at 795 nm are reported. Einstein A coefficients of the transitions are also determined. Then, all these quantities are used to determine many of the rate constants of the kinetics of energy flow and also the relative quantum yields into the low-lying electronically excited states of PuF6. In addition, the data indicate that both radiating and nonradiating states are involved in the relaxation. [ABSTRACT FROM AUTHOR]

Accurate quantum reactive scattering calculations in the full three-dimensional physical space have been carried out for the Li+FH reaction at zero total angular momentum using the adiabatically adjusting principal axis of inertia hyperspherical coordinate formalism. The procedures for fitting the potential energy surface, calculating the surface functions, and propagating the solutions in a coupled channel treatment are given and discussed. Features of the resulting reactive probability plots are analyzed, and simple explanations of a number of the quantum resonance and oscillatory features are found. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The validity of transition state theory is examined for the bimolecular reaction of Li+HF→LiF+H. Accurate three-dimensional quantum scattering theory calculations of the cumulative reaction probability are reported for energies ranging from threshold (0.255 eV) up to 0.600 eV and a total angular momentum J of 0. Transition state theory estimates of the effect of both the entrance and exit channels on the cumulative reaction probability are reported for the same energy range and J value. The transition state theory results are found to provide an accurate description of the smoothed energy dependence of the cumulative reaction probabilities with a maximum disagreement between the two calculations of about 25% arising at the highest energy considered of 0.6 eV. [ABSTRACT FROM AUTHOR]

An approximate anisotropic intermolecular potential for the Xe–SF6 interaction is developed by fitting the Morse–Morse–Morse–Spline–Van der Waals potential form to interaction virial coefficient, diffusion coefficient and collision-induced light scattering data. [ABSTRACT FROM AUTHOR]

Accurate 3D coupled channel calculations for total angular momentum J=0 for the reaction F+H2→HF+H using a realistic potential energy surface are analyzed. The reactive scattering is formulated using the hyperspherical (APH) coordinates of Pack and Parker. The adiabatic basis functions are generated quite efficiently using the discrete variable representation method. Reaction probabilities for relative collision energies of up to 17.4 kcal/mol are presented. To aid in the interpretation of the resonances and quantum structure observed in the calculated reaction probabilities, we analyze the phases of the S matrix transition elements, Argand diagrams, time delays and eigenlifetimes of the collision lifetime matrix. Collinear (1D) and reduced dimensional 3D bending corrected rotating linear model (BCRLM) calculations are presented and compared with the accurate 3D calculations. [ABSTRACT FROM AUTHOR]

Following excitation of PuF6 at 800 nm, laser-induced fluorescence (LIF) of PuF6 is observed near 2.3 μm; HF v=1 to 0 emission, arising from near resonant electronic-to-vibrational (E→V) energy transfer, is also observed with the same temporal decay as the PuF6 fluorescence. From the rise and decay times of the PuF6 and HF fluorescence and their relative intensities, all the rate constants involved in this relaxation are determined. The E→V rate constant is found to be (7.5±2.5)×103 Torr-1 s-1, and that for the relaxation of HF (v=1) by PuF6 is found to be (5.7±0.7)×103 Torr-1 s-1. [ABSTRACT FROM AUTHOR]

The quenching and energy transfer of electronically excited PuF6 by H2 and D2 have been measured using laser-induced fluorescence (LIF) from both the 1.0 and 2.3 μm emitting states of PuF6. Linear Stern–Volmer plots of the single exponential decay data give quenching rate constants (all in units of cm3 molecule-1 s-1) for D2 of (3.7±1.7)×10-15 and (8.7±0.3)×10-16 for the 1.0 and and 2.3 μm states, respectively, and a H2 quenching rate constant of (4.8±0.3)×10-14 for the 1 μm LIF. The 2.3 μm LIF in H2 is not a single exponential decay but a rapid decay followed by an anomalously long tail, which implies almost resonant E⇄V energy transfer and storage. Kinetic modeling yields the following new rate constants: PuF6*+H2→PuF6+H≠2, k=(2.05±0.30)×10-14; H2≠+PuF6→H2+PuF6*, k=(3.1±0.5)×10-14; PuF6*+H2→PuF6+H2, k=(3.1±2.0)×10-15; H2≠+PuF6→H2+PuF6, k=(3.1±3.0)×10-15; where PuF6* is the 2.3 μm emitting electronically excited state of PuF6 and H2≠ is vibrationally excited H2 in the v=1 state. [ABSTRACT FROM AUTHOR]

Accurate three dimensional quantum calculations have been carried out for the Li+HF reaction at zero total angular momentum J on a potential energy surface fitted to ab initio points. By adopting a J shifting approximation reactive cross sections are estimated and compared with the experiment. The agreement is very good. [ABSTRACT FROM AUTHOR]