Transition Spectra in the Vibrational Quasicontinuum of Polyatomic Molecules:  Raman Spectra of Highly Excited SF₆ Molecules

Abstract

The detailed studies of spontaneous Raman spectra are performed for highly excited SF6 molecules in the vicinity of the ν1 mode. Interpretation of the measured spectra is given within the framework of theoretical model, which assumes the dominating role of the statistical inhomogeneous broadening in the spectrum formation. A good agreement is achieved between the experimental and theoretical spectra throughout the whole temperature range used (T vib = 850−1660 K). A conclusion is drawn that the homogeneous broadening due to intramolecular vibrational relaxation gives a relatively small contribution to the observed spectra.

Transition Spectra in the Vibrational Quasicontinuum of Polyatomic Molecules. IR Multiple-Photon Absorption in SF6. 1. Experimental Studies

“…It turned out in particular that the statistical inhomogeneous broadening led to a Gaussian shape of the transition band profile in the quasicontinuum, distinct from the homogeneous broadening that yields a Lorentzian shape of the band profile. This approach was experimentally verified by Malinovsky et al who obtained good agreement between experimentally measured and theoretically calculated Raman spectra of the mode ν 1 in SF 6 over a wide range of vibrational temperatures ( T vib = 850−1600 K). These experiments allowed the authors to conclude that the SIB effect in SF 6 in fact made a decisive contribution to the width of the QC → QC transition band, but they failed to obtain any quantitative data as to the contribution from the homogeneous broadening.…”

“…This work is a continuation of our research (see refs and ) aimed at studying the QC → QC transitions. The width and shape of transitions of this type are mainly governed by two factors: (1) the intramolecular vibrational relaxation of the mode of interest (the active mode ν a ), which leads to the homogeneous broadening of the spectrum and (2) the fact that the excited molecule possessing a certain energy of E vib can be described by a vast set of combinations of the occupation numbers in various modes.…”

Transition Spectra in the Vibrational Quasicontinuum of Polyatomic Molecules. IR Multiple-Photon Absorption in SF6. 2. Theoretical Simulation and Comparison with Experiment

“…The correctness of the approach developed was verified by comparing between experimental and theoretical Raman spectra in the neighborhood of the frequency of the ν 1 mode of highly excited SF 6 molecules. 2 The same investigations allowed us to conclude that in SF 6 the principal contribution to the shape of transition spectra in the QC was made exactly by the SIB effect, the contribution from the homogeneous broadening associated with the IVR process being substantially smaller.…”

Intramolecular vibrational redistribution: from high-resolution spectra to real-time dynamics

“…The simplest approach consists in using IR MPE (see Section 1.3) and measuring the spectrum after a time delay ensuring the establishment of the Boltzmann distribution. This method was used for measuring the absorption spectrum in one of the bands of the C 6 F 12 molecule [312], the n 3 IR MPE spectrum of the SF 6 molecule [313], the n 1 Raman spectrum of the same molecule [314,315], and the n 1 Raman spectrum of the UF 6 molecule [316]. However, in some papers spectra were measured for narrow vibrational distributions.…”