Two‐Color Charge Transfer Transitions as a Probe of Electronic Relaxation and Photodissociation Dynamics at High Densities: Molecular Halogens in Xenon

Two‐color charge transfer transitions are developed as a probe of intermolecular potentials, electronic relaxation, and photodissociation dynamics of halogens in condensed rare gases. Two illustrative examples are given: electronic relaxation of Br 2 in liquid Xe and recombination dynamics of Cl atoms in high pressures of Xe. The Br 2 A( 3 π 1 + u ) and A'( 3 π 2 + u ) states, which are in fast equilibrium, are not quenched by the solvent in liquid Xe. In dilute solutions, they relax radiatively via the A' state with a lifetime of ∼ 100 μs. In concentrated solutions, diffusion‐controlled self‐quenching of Br 2 (A/A') proceeds with a probability of 0.07 per encounter. An encounter is found to be equivalent to four gas kinetic collisions. The photodissociation of Cl 2 and recombination of Cl atoms in gaseous Xe, 1–55 atm, are studied. The recombination kinetics is well reproduced by incorporation of diffusion‐controlled encounter frequencies in the rate constants. An equilibrium constant for formation of XeCl(X) of 2.3 × 10 −22 cm 3 is derived from the kinetic analysis.