R-variation of electronic transition moments from vibrationally crowded spectra: the B–X and D–X transitions of xenon fluoride

Abstract

Using photographic flash spectroscopy of Xe/F2 mixtures, we have studied the B(1/2)–X(2Σ+) and D(1/2)−X(2Σ+) transition of XeF in absorption between 241 and 358 nm. The spectra exhibit extensive sequence crowding due to overlapping hot bands. To determine the R-variation of the B–X and D–X electronic transition moments we use band cluster analysis, in which the R centroids of bands contributing to a given cluster are shown to be similar; i.e., the R centroid is a smoothly varying function of bandhead wavelength. Absolute transition moments are derived by normalizing our relative absorption measurements to the measured radiative lifetime of the v′=0 level of the B(1/2) state. The B–X moment is 2.70±0.22 D, independent of R between 2.30 and 2.54 Å. The D–X moment varies linearly from 2.255 D at 2.25 Å to 2.413 D at 2.50 Å (±20%). The computed radiative lifetime of the v′=0 level of the D(1/2) state is 10.0±2.0 nsec.