A REANALYSIS OF THE A(1)PI-X(1)SIGMA(+) TRANSITION OF ALBR

The A (1) Pi-X (1) Sigma(+) transition of aluminum monobromide (AlBr) near 2800 Angstrom was recorded using a Bruker IFS 120 HR Fourier tran sform spectrometer at nominal resolutions of 4 and 0.03 cm(-1). All ba nds show P, Q, and R branches and all are degraded to longer wavelengt hs. The 0-0 band is the most intense and the Delta v = 0 sequence domi nates the observed spectrum. Each band appears doubled due to the natu ral isotopic abundances of Br-79 (50.69%) and Br-81 (49.31%). Band ori gin shifts due to isotopic substitution of bromine were examined to co nfirm the assignments of isotopic species. The rotational structure of the 0-1, 1-2, 0-0, 1-1, and 2-2 bands was assigned and fitted. These data were merged with previously reported photographic data for the 1- 0, 2-1, 3-2, 2-0, and 3-1 bands and also infrared and microwave measur ements to provide an improved set of constants for both electronic sta tes. The rotational constants for each vibrational level in the X (1) Sigma(+) state vary smoothly with increasing vibrational quantum numbe r and thus an expansion of the constants in terms of equilibrium value s is recommended. An expansion of the A (1) Pi rotational constants in terms of equilibrium values is not recommended as the distortion cons tants do not change smoothly with increasing vibrational quantum numbe r. Therefore, the rotational constants for the A (1) Pi state were det ermined for each individual vibrational level. This approach leads to vastly improved vibrational constants for the A (1) Pi state by reduci ng correlations between rotational and vibrational constants. This pro blem is serious for the A (1) Pi state owing to severe departures from harmonic behavior in the v = 2 and v = 3 levels. (C) 1996 Academic Pr ess. Inc.