Product rotational distributions and specific opacity functions for the reaction Ba +HI → BaI (v=0,4,8,12,16,18) +H

Abstract

The reaction Ba+HI→BaI(v)+H was studied under beam-gas, single-collision conditions with an average center-of-mass collision energy of 13 kJ mol−1. BaI (v) rotational distributions were recorded for v=0, 4, 8, 12, 16, and 18 by means of selectively detected laser-induced fluorescence of the BaI C 2Π–X 2Σ+ band system. Each rotational distribution exhibits a maximum toward its high energy end and the range of rotational states becomes narrower as product vibration increases. Because the kinematic constraint causes almost all reagent orbital angular momentum to appear in product rotation, the principle of angular momentum conservation provides the means for determining specific opacity functions from the rotational distributions and the reagent relative velocity distribution. The specific opacity functions are narrow functions of the impact parameter. The peak values decrease smoothly from approximately 4.5 Å for v=0 to 1.5 Å for v=18, indicating a strong correlation between impact parameter and product vibrational state such that Ba+HI collisions with small impact parameter produce BaI with large vibrational excitation.