ENERGY-DISTRIBUTION AMONG REACTION-PRODUCTS .12. F+HBR-]HF(UPSILON' LESS-THAN-OR-EQUAL-TO-4)+BRSTAR(2P3/2,2P1/2)

As part of a study of product energy distributions in the family of reactions F + HX → HF(v′, J′) + X (X Cl, Br, I) we have studied the second reaction in this family, F + HBr → HF(v′,J′) + Br(2P 3 2, 2P 1 2) (2) using the arrested relaxation variant of the infrared chemiluminescence approach to obtain the detailed rate constant k(V′, R′, T′) (V′, R′, T′ are product vibrational, rotational and translational excitation), as well as the fraction of reaction yielding excited electronic state atomic product (reaction (2b), → Br*(2P 1 2)). The product vibrational excitation is indicative of quite different reaction dynamics for reaction (2) as compared with reaction (1) [(1) was F + HCl, studied previously by the same technique]. Reaction (1) favoured the formation of vibrationally excited product; reaction (2) gives rise predominantly to product with low vibrational excitation. With respect to this product-attribute the reaction F + HBr (2) gives a markedly more-nearly statistical outcome than does reaction (1). If, however, the observed product rotational distribution is used as an index of behaviour, the outcome of the reaction F + HBr (2) is markedly less statistical than is the rotational distribution in the product of reaction (1). The mean fractions of the available energy entering vibration, rotation and translation for reaction (2) were found to be (f′V) = 0.24, (f′R) = 0.09 and (f′T) = 0.67. The fraction of reaction (2) which proceeds on the upper energy-surface to yield Br* (with energy, 10.5 kcal mole-1 in excess of Br) is k*/k = 7 ± 3‰. © 1979.