ANALYSIS OF THE BABRC2PI1/2,3/2-X2SIGMA+ TRANSITION UP TO HIGH (V CONGRUENT-TO 74) VIBRATIONAL QUANTUM STATES BY LASER-INDUCED FLUORESCENCE

Excitation spectra of the BaBrC2Π 1 2, 3 2-X2Σ+ transition were measured by the method of laser-induced fluorescence (LIF). The BaBr (X2Σ+) molecules were thereby produced in a molecular beam apparatus by exothermic reactions of barium atoms with the following bromine compounds: CH3Br, CH2Br2, CHBr3, CBr4, and HBr, giving BaBr product molecules which have very different population distributions depending on the reaction (1). Vibrational bands were resolved up to v″ = 74 for the sequence Δv = -1 of the C2Π 1 2-X2Σ+ transition and up to v″ {reversed tilde equals} 50 for the sequences Δv = 0 and -1 of the C2Π 3 2-X2Σ transition. A linear fit to the vibrational spacings, ΔG, in the range v = 0 through 50 leads to the following spectroscopic constants (in cm-1): X2Σ+: ωe″ ωex″=0.4312, C2Π 1 2: ωe′=195.83 ωex′=0.4290, Te=18 648.5, C2Π 3 2: ωe′=197.00, ωex′=0.4214, Te=19 192.8. The difference of the rotational constants could be determined to be B″e - B′e {reversed tilde equals} 0.004 ± 20%, while the absolute value of these constants could only be extrapolated from other metal halide molecules, giving Be {reversed tilde equals} 0.042. The close similarity of the vibrational-rotational constants of the three electronic states, X2Σ+ and C2Π 1 2, 3 2, underlines the Rydberg character of these states, for which probably a nonbonding electron in the BaBr molecule is responsible. © 1979.