Laser-initiated chemical reactions: Cl+H2S→HCl+HS: Rate constant, product energy distribution, and direct detection of a chain mechanism

Laser-initiated, time-resolved infrared chemiluminescence techniques are used to study the detailed kinetics of chlorine/hydrogen sulfide systems. Measurements on the Cl+H2S→HCl+HS reaction are carried out by pulsed laser photolysis of S2Cl2→S2Cl+Cl in a flowing mixture with H2S, while detecting vibrational chemiluminescence from the HCl product. The measured rate constant for the Cl+H2S reaction is 6.0 ±1.2×10−11 cm3 molecule−1 sec−1 at 296°K. The vibrational product distribution is predominately excitation of HCl to v=1 and v=2, with the ratio (v=1):(v=2) =15. The dynamical interpretation of the Cl+H2S reaction data is discussed. Photolysis of Cl2→2Cl in the presence of H2S produces a rapid chain reaction, Cl+H2S→HCl+HS, HS+Cl2→HSCl+Cl. The chain mechanism and its real time development are observed directly from the product chemiluminescence signal.