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Transition Spectra in the Vibrational Quasicontinuum of Polyatomic Molecules. IR Multiple-Photon Absorption in SF6. 2. Theoretical Simulation and Comparison with Experiment
Ist Teil von
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 1999-12, Vol.103 (51), p.11299-11309
Ort / Verlag
American Chemical Society
Erscheinungsjahr
1999
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
The IR MP excitation spectra of the SF6 molecule in the vibrational quasicontinuum (QC) measured experimentally in the vicinity of the ν3 mode frequency are compared with their theoretical counterparts with a view to revealing the relative contribution from the statistical inhomogeneous broadening (SIB) and homogeneous broadening to the formation of the IR transition spectra in the QC. The IR MP spectra are found by solving rate equations, the cross sections of the successive transitions being calculated in the SIB approximation. The half-width γL of the Lorentzian profile associated with the homogeneous broadening is the only adjustment parameter of the model. A good agreement (within the accuracy of measurement) is obtained between the experimental and theoretical IR MP spectra over a wide range of spectral and energy parameters. The γL values are found which vary within the limits 0.53 ≤ γL ≤ 10.2 cm-1 in the energy range 4500 ≤ E ≤ 30 000 cm-1. The conclusion is drawn that the main parameters of the IR transition spectra in the QC (the position of the maximum, width, and intensity) are governed largely by the SIB effect, though the Lorentzian wings may play a decisive role when excitation occurs at the edges of the spectrum. The IR transition cross sections found are used to compute the IR MP excitation dynamics in the QC and determine the vibrational distribution function being formed. It is found that excitation in the QC may also give rise to a nonequilibrium bimodal distribution.