Tandem Chemical Laser Measurements of Vibrational Energy Distribution in the Dichloroethylene Photoelimination Reactions

Abstract

Equal‐gain temperature measurements with two laser tubes in the same optical cavity (a ``tandem'' laser) are described. In this way, rate constant ratios can be measured for vibrational transitions that do not have highest gain. The HCl laser emissions caused by photolysis of the 1, 1‐ and cis‐1, 2‐dichloroethylenes were examined in this manner. For 1, 1‐dichloroethylene, k 3 /k 2 =0.85± 0.02 and k 2 /k 1 =1.08± 0.03 and for cis‐1, 2‐dichloroethylene, k 3 /k 2 =0.71± 0.03 and k 2 /k 1 =0.76± 0.02 . The trends confirm the earlier inference that HCl vibrational excitation is more significant in the 1, 1‐dichloroethylene photo‐elimination, with the attendant implication that HCl vibrational excitation tends to favor, 1, 1 addition (Markovnikov addition) in the reverse reaction between HCl and monochloroacetylene.