Recombination of Br Atoms by Flash Photolysis over a Wide Temperature Range. II. Br2 in He, Ne, Ar, Kr, N2, and O2

Recombination rate constants of Br atoms in helium, neon, argon, krypton, nitrogen, and oxygen have been measured with an accuracy of approximately ± 10% from room temperature up to 1275°K using a flash photolysis technique. The temperature dependences of the rate constants can be expressed by the following equations: logkrHe = (9.066 ± 0.018) − (1.261 ± 0.043) log(T / 300), logkrNe = (9.170 ± 0.024) − (1.423 ± 0.057) log(T / 300), logkrAr = (9.381 ± 0.016) − (2.287 ± 0.125) log(T / 300) + (1.154 ± 0.194) log2(T / 300), logkrKr = (9.489 ± 0.021) − (2.77 ± 0.179) log(T / 300) + (1.473 ± 0.298) log2(T / 300), logkrN2 = (9.499 ± 0.034) − (2.208 ± 0.253) log(T / 300) + (0.889 ± 0.405) log2(T / 300), logkrO2 = (9.767 ± 0.021) − (1.583 ± 0.057) log(T / 300), where kr is in units of liter2 mole−2·second−1 and T is absolute temperature. At room temperature, the results for krHe, krAr, krN2, and krO2 agree with the literature; direct measurements of krNe and krKr have not been previously reported. The results are explained in terms of a mechanism, involving a complex intermediate BrM, where M is a third body. It is shown that the BrM complexes in bound and metastable states as well as BrM quasidimers may contribute to the recombination. A comparison of calculated and experimental rate data suggest that the interaction potentials between Br and M are several times larger than that between Kr and M. Although a satisfactory agreement between calculated and experimental rates could be obtained by setting steric factor for the reaction to P = 0.5, a better agreement is achieved if P is treated as a temperature-independent parameter. The efficiencies of Br and Br2 as third bodies in Br-atom recombination have also been studied. When the present data are combined with the available shock-wave data, the variation of krBr2 and krBr with temperature between 300 and 2985°K can be described bylogkrBr2 (liter2mole−2·sec−1) = (10.89 ± 0.85) − (3.01 ± 0.28) log(T / 300), logkrBr (liter2mole−2·sec−1) = (12.22 ± 2.00) − (4.3 ± 0.62) log(T / 300).