Table of Contents
Laser Chemistry
Volume 2, Issue 5-6, Pages 285-307

Ionic State Relaxation Processes in VUV-Excited Polyatomic Molecules

1Laboratoire de Photophysique Moléculaire du C.N.R.S., Bâtiment 213, Université Paris-Sud, Orsay Cedex 91405, France
2Départment d'Astrophysique Fondamentale, Observatoire de Paris-Meudon, Meudon 92190, France

Copyright © 1983 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Advantages of molecular ions for the study of electronic radiationless transitions are discussed. Several coincidence techniques for measuring key relaxation parameters are briefly described. The different cases of radiationless transition studies of molecular ions are outlined and examples mentioned. Coincidence measurements between threshold photoelectrons and ion fluorescence photons emitted by VUV-excited hexafluorobenzene are presented. The radiative, kr, and nonradiative, knr, relaxation rates for specific vibrational levels in the B2A2u and C2B2u states of C6F6+ are derived from the measured lifetimes and quantum yields of ion fluorescence. The kr rate for excitation of the C, 0° level is found to be about 25% of that for the B2A2u state where kr = (18±3) × 106 s−1. The knr rates for the 1n and 1n21 progressions in the B state increase with n but exhibit a mode selective behavior. Model calculations of knr confirm the mode selectivity. These calculations were carried out on a noncommunicating, harmonic oscillator basis. Progressive deviations between experimental and calculated results are interpreted as indicating the gradual onset of vibrational redistribution with increasing vibrational energy. The results illustrate a new method for demonstrating the growing in of intramolecular vibrational relaxation.