Relaxation of HCl(v= 1) and DCl (v= 1) by chlorine atoms at temperatures between 195 and 400 K

Abstract

A pulsed HCl chemical laser has been used to excite HCl in the presence of known concentrations of Cl atoms in a discharge-flow apparatus. By observing the subsequent vibrational fluorescence as a functions of time, rates of relaxation of HCl(v= 1) by Cl atoms were determined at temperatures between 195 and 400 K. The values of the rate constant, k_1,H, can be matched quite well by the Arrhenius expression: k_1,H= 9.0 (^+1.8_–1.6)× 10^–11 exp(–5.8 ± 0.5 kJ mol^–1/RT)cm³ molecule^–1s^–1. Similar experiments on DCl yielded k_1,D= 2.4(^+0.6_–0.5)× 10^–11 exp(–3.2 ± 0.9 kJ mol^–1/RT) cm³ molecule^–1 s^–1. Possible mechanisms for these unusually rapid relaxation processes are considered.