Fourier Transform Emission Spectrum of the Triplet System of BH

Author Institution: Edwards AFB, CA 93524-7680.The $b^{3}\Sigma^{-}-a^{3}\Pi$ system of BH, near $3700 {\AA}$, has been observed in emission from a Corona Excited Supersonic Expansion of dilute diborane in helium. The spectrum was recorded at Doppler limited resolution $(0.14 cm^{-1})$ with the 1m Fourier transform spectrometer at Kitt Peak National Observatory. Very strong spectra of the $\Delta \nu = 0$ sequence (0-0 through 5-5 bands) were observed providing much improved line positions and molecular constants. The much weaker off-diagonal bands were recorded at $0.85 cm^{-}1$ resolution using a monochromator and OMA. The $\Delta \nu=+1$ sequence was observed out to 8-7 and the $\Delta \nu=0$ sequence was extended to 7-7. The RKR potential curves determined from this data extend to 80% of the dissociation limit for the $a^{3}\Pi$ state and 70% for the $b^{3}\Sigma^{-}$ state. Comparisons will be made between the observed intensities of the different bands and theoretical calculations by Pederson et al. of the transition moments, and predissociation rates to the repulsive $(1)^{3}\Sigma^{+}$ state