Zeitschrift für Physikalische Chemie, 214, 11, 1501-1519 (2000)  by Oldenbourg Wissenschaftsverlag, München Collisional Deactivation of Highly Vibrationally Excited SO 2 : A Time-Resolved FTIR Emission Spectroscopy Study By Dong Qin a, 1 , Gregory V. Hartland b, 1 , Carl L. Chen 2 and Hai-Lung Dai 1, * 1 Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA 2 Department of Advanced Technology, Brookhaven National Laboratory, Upton, New York 11973, USA (Received June 8, 2000; accepted in revised form July 31, 2000) SO 2 / IR Emission / High Vibrational Levels / Energy Transfer Time-resolved Fourier transform IR emission spectroscopy, capable of 10 -8 s and 0.1 cm -1 spectral resolution, has been used to study the collisional deactivation of highly vi- brationally excited SO 2 by bath-gas molecules Ar, N 2 ,O 2 , CO 2 and SF 6 . The vibrationally excited SO 2 were initially prepared with 32,500 cm -1 energy in the X ˜ 1 A 1 state by the pulsed 308 nm laser excitation followed by internal conversion. The entire collisional deactivation process of the excited SO2 was monitored by time-resolved IR emission spectra through the IR active transitions. The average energy, E, of excited SO2 was extracted from the IR emission bands using known vibrational constants and selection rules. E is further used to derive the average energy loss per collision, ∆E, by each of the bath-gas molecules. The results show that ∆E increases from mono- and di- atomic quenchers to more complex polyatomic molecules, as V-V energy transfer contrib- utes to V-T/R. For all bath molecules, ∆E increases with E and displays a marked increase at E 20,000 cm -1 . The observed threshold behavior most likely arises from intramolecular vibronic coupling within SO 2 and implies the importance of long range interaction in intermolecular energy transfer. 1. Introduction Collisional deactivation of highly vibrationally excited molecules by ambi- ent bath molecules, a subject of research pioneered by Troe and coworkers * Corresponding author. E-mail: dai@sas.upenn.edu a Present address: Center for NanoTechnology, University of Washington, Seattle, WA, 98195-2140, USA b Present address : Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA Unauthenticated Download Date | 7/2/16 1:06 AM