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

摘要

Rate constants and initial HBr and HF product distributions for the title reactions were measured in a fasthyphen;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(vges;1) and HF(vges;1) formation, relative to the H+Cl2reaction, are 3.3, 0.39, 0.50, 3.4, and 0.003, for Br2, SF5Br, PBr3, SF5, and SF4, respectively. This directly measured Br2rate 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+Br2corresponds to lang;fVrang;=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 lang;fVrang;=0.36. The low vapor pressure of PBr3limited the lsqb;PBr3rsqb; and high lsqb;Hrsqb; was required to observe HBr emission; correcting the observed distribution for vibrational relaxation gives lang;fVcong;0.47. These lang;fVrang; values include estimates for HBr(v=0). Based upon the highest HBr level observed from SF5Br and PBr3, D0(Brndash;SF5)55 and D0(Brndash;PBr2)62 kcalthinsp;moleminus;1. The HF vibrational distributions from SF5and SF4decline with increasingv, which suggests that these reactions proceed via a longhyphen;lived complex. For these cases the formation of HF(v=0) is important, and significant corrections must be made to the HF(vges;1) formation constants to obtain the total HF formation rate constants. The rate constants and energy disposal data are used to discuss models and to compare the H+Br2reaction to H+Cl2and F2.