Radiative and Nonradiative Decay of the BH(b3Σ-) State: A Joint Experimental and Theoretical Study

Abstract

Lifetimes of rotational/fine-structure levels of electronically excited BH(b3Σ-), in vibrational levels v‘ = 0−4, were determined from fluorescence decay waveforms with laser excitation on isolated rotational lines in the b3Σ-−a3Π Δv = 0 sequence. BH was prepared in a pulsed supersonic beam by 193 nm photolysis of diborane. The measured lifetimes were compared with values obtained from a theoretical treatment of the excited state dynamics, in which both radiative decay to the a3Π state and nonradiative decay through the repulsive 13Σ+ state were considered. The experimental and theoretical lifetimes agree very well. This comparison shows that the low b3Σ- rotational levels for v‘ = 0−2 decay purely radiatively, with a rate decreasing as v‘ increases. These rates are virtually independent of the fine-structure level. However, the lifetimes of the higher vibrational levels exhibit significant fine-structure level dependence, with the shortest values obtained for the F2 levels. This behavior is shown to be a...