Reactions of Hot Hydrogen Atoms in Gaseous Hydrogen Chloride and Hydrogen Bromide

Abstract

Hydrogen atoms of initial kinetic energy E0 = 1.15 or 2.1 eV were produced photolytically and their reactions with HCl were studied at 300 °K using bromine as a scavenger. The fraction, FH, undergoing reaction 2 while hot was found to be 0.79 ± 0.02 and 0.55 ± 0.02 for E0 = 2.1 and 1.15 eV, respectively.[Formula: see text]For 2.1 eV atoms a similar result was obtained at 200 °K with chlorine as scavenger. On the addition of carbon dioxide as a moderator FH decreased in a manner consistent with the kinetic theory of hot atom reactions. Comparison of the present results with previous work on the D + DCl abstraction reaction showed that the cross section of the latter is probably 20 to 50% higher than that of H + HCl. The cross section of reaction 2 appears to increase with energy over most of the 0.1 to 1.1 eV range and possibly also above it. Its average magnitude over this energy region was estimated to be [Formula: see text].For atoms of E0 = 1.15 eV reacting in HBr FH is close to unity. The threshold of reaction 3′[Formula: see text]is near zero energy and its cross section rises rapidly, becoming [Formula: see text] in the thermal region for 300 °K.