Experimental determination of the specific opacity function for the Ba+HI→BaI(v=0)+H reaction

Abstract

Through the use of laser-induced fluorescence spectroscopy, product rotational population distributions were recorded for the Ba(1S0)+HI(X 1Σ+)→BaI(X2 Σ+,v=0)+H(2S1/2) reaction under well-defined, crossed-beam conditions. In this kinematically constrained reaction, orbital angular momentum of the reagents Lreag is channeled almost exclusively into rotational angular momentum of the products Jprod. Consequently, ‖Jprod‖≂μvrelb, where μ is the reduced mass of the reactants, vrel is their relative velocity, and b is the impact parameter of the reactive collision. For relative velocity distributions with mean values ranging from 860 to 1000 m s−1, the BaI v=0 rotational distributions were found to peak sharply at high J values (≳420). Nonlinear least-squares analysis showed the specific opacity function (impact parameter distribution) for the formation of vibrationless BaI product to be exceptionally narrow (∼0.3 Å FWHM) with a pronounced maximum at the highest energetically allowed impact parameter ∼4.5 Å.