SPECTRA, RADIATIVE LIFETIMES, AND BAND OSCILLATOR STRENGTHS OF THE $A^{1}\Pi-X^{1}\Sigma^{+}$ TRANSITION OF BH

$^{1}$ W. T. Luh and W. C. Stwalley, J. Mol. Spectrosc. 102, 212 (1983). $^{2}$ G. H. L. Diercksen, N. E. Gruner, J. R. Sabin, and J. Oddershede, Chem. Phys. 115, 15 (1987).Author Institution: Applied Research Corporation, 8201 Corporate Drive; Chemistry Division, Naval Research LaboratorySeveral vibrational bands of the $A^{1}\Pi-X^{1}\Sigma^{+}$ transition of the BH radical produced by 193 nm photolysis of $BH_{2}CO$ have been examined. Diagonal ($\Delta v=0$) and off-diagonal ($\Delta v= \pm _{3}$) bands have been observed using LIF techniques. The new spectroscopic features reported here are excitation spectra of the 0-1 and 1-2 bands. Relative strengths of the various bands were assessed by collecting dispersed emission spectra. Ratios of Einstein emission coefficients, vibrational transition probabilities, and band absorption oscillator strengths were calculated comparing the 0-0 and 0-1 bands and comparing the 1-0, 1-1, and 1-2 bands. The ratios indicate that transitions occur mainly in the diagonal elements; the off-diagonal elements are two orders of magnitude less intense. Radiative lifetimes were measured by observing the fluorescence decay over 5-6 lifetimes. The radiative lifetimes of the v'=0,1, and 2 levels have been measured to be $127 \pm 10 ns, 146 \pm 12$ ns, and $172 \pm 14$ ns respectively. The Einstein emission coefficient ratios and the lifetime values have been combined to yield Einstein emission coefficients and band oscillator strengths for five bands. The Einstein emission coefficients and lifetime values are compared to previous experimental results and to theoretical calculations of Luh and Stwalley1 and to the second order polarization propagator results of Diercksen $et al ^{2}$. In some cases, large differences are observed. Our results allow us to assess the accuracy of the transition moments and potential energy curves presently in the literature