FOURIER-TRANSFORM EMISSION-SPECTROSCOPY OF THE A(2)PI-X-2-SIGMA(+) SYSTEM OF BEH

The A (2)Pi-X (2)Sigma(+) transition of BeH was observed by Fourier tr ansform emission spectroscopy using a hollow cathode discharge lamp. T he 0-0 to 6-6 bands were rotationally analyzed and molecular constants extracted. The equilibrium rotational constants B-e and bond lengths were found to be 10.331 21(50) cm(-1) and 1.341 68(3) Angstrom for the ground state and 10.466 31(27) cm(-1) and 1.332 99(2) Angstrom in the excited state. In order to link the diagonal bands together and to de termine the vibrational constants, the 0-1 to 6-7 bands in an archival are emission spectrum were also rotationally analyzed. In the X (2)Si gma(+) and A (2)Pi states, the spectroscopic constants are nearly iden tical so the Delta nu = -1 bands were too weak to be seen in our Fouri er transform spectra. Franck-Condon factors were calculated for the A (2)Pi-X (2)Sigma(+) transition from Rydberg-Klein-Rees potential curve s. These new rotational analyses now link up with the previous work on the 0-7, 0-8, 0-9, 1-9 and 1-10 bands of the C (2)Sigma(+)-X (2)Sigma (+) system [R. Colin, C. Dreze, and M. Steinhauer, Can. J. Phys. 61, 6 41 (1983)]. Spectroscopic data are thus available for all bound ground state vibrational levels, upsilon'' = Q-10, and a set of Dunham Y con stants were determined. BeH joins the small group of chemically bound molecules for which a nearly complete set of ground state rovibronic e nergy levels are known experimentally. (C) 1998 American Institute of Physics.