15min:

C. MUKARAKATE, C. TAO, M. DESELNICU AND S. A. REID, Department of Chemistry, Marquette University, P.O. Box 1881, Milwaukee, WI 53201-1881.

We obtained single vibronic level (SVL) emission spectra following excitation of bands in the progressions 2₀ⁿ, 2₀ⁿ3₀^m, 1₀¹2₀ⁿ, and 1₀¹2₀ⁿ3₀^m in the A¹A''-X¹A' system of CHBr and CDBr. The carbenes were generated using a pulsed discharge source, and SVL emission spectra obtained using a 0.3 m spectrograph in combination with a gated, intensified CCD detector. These spectra reveal rich new detail regarding the vibrational structure of the X¹A' and a³A'' states, and spin-orbit induced mixing between them, up to 9000 cm^-1 above the vibrationless level of the X¹A' state. For both isotopomers we observe more than twice the number of levels previously reported, and the results of Dunham expansion fits to the vibrational term energies, and comparisons with previous experimental and theoretical studies, will be reported. Our results lead to several revised assignments, including the X¹A' state C-H stretching fundamental. For both isotopomers we observe almost every possible X¹A' level below 4000 cm^-1. Unlike CHBr, where even the lowest bending level is strongly perturbed, every level save one below 3000 cm^-1 in CDBr is reproduced by a Dunham expansion fit to within our experimental uncertainty. However, the spin-orbit mixing is extensive above 4000 cm^-1 in both isotopomers, and many unassigned lines remain. The derived vibrational parameters of the X¹A' and a³A'' states are in excellent agreement with ab initio predictions, including our own DFT calculations.