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

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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 〈fV〉=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 〈fV〉=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 〈fV≅0.47. These 〈fV〉 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"...

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