Rate constants and vibrational energy disposal for reaction of H atoms with Br2, SF5Br, PBr3, SF5, and SF4

Abstract

Rate constants and initial HBr and HF product distributions for the title reactions were measured in a fast‐flow apparatus using infrared chemiluminescence techniques. The spectra were interpreted using a new set of Einstein coefficients for HBr, which are listed in the Appendix. The rate constants for HBr(v⩾1) and HF(v⩾1) formation, relative to the H+Cl₂ reaction, are 3.3, 0.39, 0.50, 3.4, and 0.003, for Br₂, SF₅Br, PBr₃, SF₅, and SF₄, respectively. This directly measured Br₂ rate constant supports the smaller values that have been estimated in the literature. The initial HBr vibrational distribution (v1:v2:v3:v4:v5=0.03:0.20:0.40:0.31:0.06) from H+Br₂ corresponds to 〈f_V〉=0.49. The observed HBr vibrational distributions (v1:v2:v3:v4) are 0.28:0.43:0.23:0.06 and 0.63:0.24:0.13 for SF₅Br and PBr₃, respectively. The SF₅Br results are close to the initial distribution and give 〈f_V〉=0.36. The low vapor pressure of PBr₃ limited the [PBr₃] and high [H] was required to observe HBr emission; correcting the observed distribution for vibrational relaxation gives 〈f_V≅0.47. These 〈f_V〉 values include estimates for HBr(v=0). Based upon the highest HBr level observed from SF₅Br and PBr₃, D⁰(Br–SF₅)0(Br–PBr₂)−1. The HF vibrational distributions from SF₅ and SF₄ decline with increasing v, which suggests that these reactions proceed via a long‐lived complex. For these cases the formation of HF(v=0) is important, and significant corrections must be made to the HF(v⩾1) <named-content xmlns:mml="http://www.w3.org/1998/Math/MathML"...