Dissociation dynamics of I2(B)–Ar: Rotational population distributions of I2(B,v) fragments from the T-shaped and linear complexes

Abstract

Optical-optical double resonance techniques have been used to examine the dissociation dynamics of I2(B)–Ar. Rotational population distributions were characterized for the I2(B,v) fragments. Vibrational predissociation of the T-shaped complex yielded fragments with smooth rotational distributions. The high-energy limits of the distributions were consistent with events that channeled almost all of the available energy into product rotation. These data indicate a dissociation energy for I2(B)–Ar of D0(C2v)=220 cm−1. Most initial states of the complex produced bimodal rotational population distributions, but a few gave Boltzmann-type product distributions. The dependence of the character of the distribution on the initially excited state suggests that predissociation is mediated by intramolecular vibrational energy redistribution. Dissociation of linear I2(B)–Ar yielded fragments with Boltzmann type rotational population distributions. Excitation of the complex within the bound regions of the B–X transition gave rotationally cold I2(B,v) fragments, consistent with direct dissociation from a near-linear geometry. Excitation above the B state dissociation limit produced I2(B,v) fragments via caged recombination. The rotational distributions of these fragments were cold, supporting earlier studies that attribute the one atom cage recombination to the linear isomer.