Rotational energy effect upon the branching fraction for reactive decay of the RbF+K collision complex

Abstract

The influence of the rotational energy of the RbF molecule upon its reactivity with K has been measured by the crossed molecular beam technique over a range of relative translational energy ?_tr from 3.0–4.5 kcal mol⁻¹. The experiments involve the exoergic reaction RbF+K?[RbFK]→Rb+KF+1.5 kcal mol⁻¹, for which the reactive branching fraction F_R(?_tr) had been previously measured using velocity‐selected but otherwise ’’thermal’’ beams. Following procedures similar to those of Stolte et al. (1977), rotationally cold (’’low‐J’’) beams of RbF have been prepared (by a quadrupole state selector) and crossed with a K beam. The reactive yield (Rb flux) and thus the reactive branching fraction F_R is found to be significantly greater for the ’’low‐J’’ beam than for the ’’thermal’’ beam of RbF. The magnitude of this rotational energy effect, associated with a reduction of some 2.0 kcal mol⁻¹ in the rotational energy of the reagent molecules, is similar to the effect of a comparable reduction in ?_tr. Thus, within the uncertainty of the present results, rotational energy of the RbF is equivalent in importance with relative translational energy in influencing the decay of the RbFK collision complex.