Energy disposal by F atom abstraction reactions: HF vibrational–rotational distributions from F+HBr and HI

Abstract

HF infrared chemiluminescence from the reactions of F atoms with HCl, HBr, and HI was used to assign vibrational–rotational populations of the HF product. Experiments were done in both a cold‐wall, arrested vibrational–rotational relaxation apparatus and in a fast‐flow, arrested vibrational relaxation apparatus. Since the total HF formation rate constants are known for these reactions, absolute 300 K rate constants for formation of HF_vJ are established. The mean vibrational energy disposal to HF including estimates for HF (v=0) is <f_V≳_HCl=0.51, <f_V≳_HBr=0.59 and <f_V≳_HI=0.59. The mean HF rotational energy decreased from 0.18 to 0.12 in the HCl–HI series. The <f_V+f_R≳ sum is virtually constant for the three reactions, but <f_V≳ does increase slightly as the reactions become more exoergic. The HBr reaction yields ∼10% Br(²P_1/2), the upper spin–orbit state; but I(²P_1/2) is not formed from HI. Independent work by Nip and Clyne on the HCl reaction suggest that Cl(²P_1/2) also is formed in ∼10% yield. The dynamics of these reactions are considered with the aid of information‐theoretic analysis. The possibility of two components, direct and complex, for product formation is considered. The HF vibrational distribution from the HBr and HI experiments in the cold‐wall apparatus showed an unusual dependence upon reagent flow and the ’’best’’ distributions were not found for the lowest flow. The selection of the ’’best’’ initial vibrational populations were assisted by the data from the fast‐flow apparatus, which included experiments with DCl and DBr as well as HCl, HBr, and HI.