Relative energies and collisional kinetics of the B(Ω = 1/2) and C(Ω = 3/2) excited states of xenon fluoride as studied by laser-induced fluorescence

A pulsed nitrogen laser photodissociated F₂ in the presence of Xe, and the resulting ground-state XeF was excited by a second pulsed, tunable dye laser in the 0,4 and 0,5 bands of the B(1/2)-X(1/2) transition. Both dispersed fluorescence spectra and tunable laser excitation spectra, taken by using a gated detection system, show that the C state is lower in energy than the lowest vibrational level of the B state. The ratio of fluorescence intensities in the C-A and B-X transitions was measured as a function of xenon and argon pressure. An analytical model was developed for the time dependence of the B and C state concentrations after instantaneous excitation and in the presence of intersystem crossing, quenching, and radiative decay. Published rate constants for the excited state kinetics of XeF(B) and XeF(C) are reviewed, and model calculations of the measured intensity ratio are used to assess these rate constants. A critique of using intensity ratios in pulsed or steady-state experiments to determine the XeF B-C energy separation is presented.