Energy partitioning in photodissociation: state selective studies of the cyanogen halides

Abstract

A systematic analysis of the vacuum ultraviolet absorption spectra of ClCN, BrCN and ICN, based on measurements of polarised, photofragment fluorescence, has been extended and used to probe the influence of initial state selection on vibrational, rotational (and by energy conservation, translational) energy disposal in the molecular fragments. Measurements have been conducted on channels leading to CN(A²Π_i) as well as CN(B²Σ⁺) and the contrasting behaviour following excitation into intravalence dissociation continua and into predissociated band systems has been characterised. Energy distributions are found to be sensitive to the nature of the photoexcited state rather than simply its energy [though the CN(A) and CN(B) channels exhibit parallel behaviour] and the qualitative utility of the generalised Frank–Condon description of the dissociation process has been confirmed.