B-state excimer production following rare-gas halide trimer absorption.

Experiments were recently reported which suggested that at certain wavelengths, the excimer B state is populated following photodissociation of the associated trimer. For the cases of Xe₂Cl and Kr₂F absorption, strong fluorescence from the excimer B states was observed following trimer absorption at 308, 337, and 351 nm, and the branching ratio for this process was determined to be 1. At 248 and 193 nm, little or no fluorescence was observed, but the transition wavelengths where the branching ratio became large could not be determined. A frequency-doubled dye laser has allowed the branching ratio for the formation of the excimer B state following trimer absorption to be measured continuously from 220 to 450 nm. Laser-induced fluorescence from the B state was monitored as a function of the dye-laser wavelength, allowing the branching ratio to be calculated. In the Xe₂Cl studies, an XeCl laser served to photodissociate Cl₂ and photodissociate XeCl pairs, directly producing XeCl B-state molecules. The B→X transition was then monitored shortly after the dye laser was fired at the peak of the Xe₂Cl^* fluorescence. Results of these experiments demonstrate the need for a revision of trimer potential-energy curves to be made.