Laser-induced fluorescence from weakly bound states of KI

Abstract

Broad-band fluorescence from a molecular beam of KI has been observed following excitation with 222.1 and 248.5 nm excimer laser radiation. For 248.5 nm excitation an emission was observed corresponding to KI^∗ in the first weakly bound state. Kinetic studies showed this to be the product of photodissociation of the dimer (KI)₂. By contrast, the 222.1 line excited monomeric KIdirectly into a previously unknown weakly bound state. Three distinct domains of emission are reported originating in this latter excitation: (i) an intense vibrational progression in the ultraviolet, (ii) diffuse bands in the blue-green, and (iii) continuous emission to the red of the K (4²P→4²S) lines. We have attributed these spectra to (i) direct fluorescence into the ground state, (ii) cascade fluorescence between the prepared state and an intermediate weakly bound state, and (iii) cascade fluorescence to dissociative states. The upper state well depth was estimated to be 500 cm^-1 using Franck-Condon simulation of the spectrum in the ultraviolet.