Vibrational energy and bimolecular reactions: Enhancement of the electron transfer derived product channels for quenching of Xe(3P2) and Kr(3P2) atoms by CFnCl4−n, C2FnCl6−n, and CF3CFClCF2Cl

Abstract

The yields of XeCl(B,C) and KrCl(B,C) from the reactions of Xe(3P2) and Kr(3P2) metastable atoms with chlorofluoromethanes and chlorofluoroethanes are enhanced by the addition of vibrational energy to the molecule. The reactions were studied in a fast flow reactor with He or Ar carrier gas; vibrational energy was added to the molecules by multiphoton absorption from a CO2 laser pulse at fluences of 0.2–1.0 J cm−2. The enhancement of the XeCl(B,C) or KrCl(B,C) product was observed by monitoring the B–X fluorescence intensity in real time following excitations by the CO2 laser. Enhancement factors are reported for reactions with CF2Cl2, CFCl3, CF3CFCl2, CF2ClCF2Cl, CF2ClCFCl2, and CF3CFClCF2Cl; survey experiments are presented to demonstrate enhancement of XeCl* and XeBr* from vibrationally excited CF2BrCl and CF3CH2Br. The decay times of the XeCl(B) and KrCl(B) signals provide information about the relaxation rates of the vibrationally excited CFnCl4−n and C2FnCl6−n molecules. In order to have a reliable reference, the total quenching rate constants and the branching fractions for XeCl(B,C) and KrCl(B,C) formation for 300 K conditions also were measured for most of the compounds; the branching fraction for XeCl* formation form CF3CCl3 is large for a polyatomic molecule.