Fluorescence excitation and emission spectroscopy of the (A)over-cap1A" ← (X)over-cap1A′ system of CHBr -: art. no. 134302

We report fluorescence excitation and emission spectra of CHBr in the 450-750 nm region. A total of 30 cold bands involving the pure bending levels 2(0)(n) with n=2-8 and combination bands 2(0)(n)3(0)(1)(n=1-8), 2(0)(n)3(0)(2)(n=1-6), 2(0)(n)3(0)(3)(n=1-2), 1(0)(1)2(0)(n)(n=5-7), 1(0)(1)2(0)(n)3(0)(1)(n=4-6), and 1(0)(1)2(0)(n)3(0)(2)(n=5) in the A (1)A(')<- X (1)A(') system were observed, in addition to a number of hot bands. The majority of these are reported and/or rotationally analyzed here for the first time. Spectra were measured under jet-cooled conditions using a pulsed discharge source, and rotational analysis yielded band origins and rotational constants for both bromine isotopomers (CH Br-79,CH Br-81). The derived A (1)A(') vibrational intervals are combined with results of [Yu J. Chem. Phys. 115, 5433 (2001)] to derive barriers to linearity for the 2(n), 2(n)3(1), and 2(n)3(2) progressions. The A (1)A(') state C-H stretching frequency is determined here for the first time, and the observed nu(3) dependence of the Br-79-Br-81 isotope splitting in the A (1)A(') state is in good agreement with theoretical expectations. Our dispersed fluorescence spectra probe the vibrational structure of the X (1)A(') state up to similar to 9000 cm(-1) above the vibrationless level; the total number of levels observed is more than twice that previously reported. As first reported by [Chen J. Mol. Spectrosc. 209, 254 (2001)], these spectra reveal numerous perturbations due to spin-orbit interaction with the low-lying a (3)A(') state. The results of a Dunham expansion fit of the ground state vibrational term energies, and comparisons with previous experimental and theoretical studies, are reported. Our results lead to several revised assignments, including the X (1)A(') C-H stretching fundamental. Globally, the vibrational frequencies of X (1)A('), a (3)A('), and A (1)A(') are in excellent agreement with theoretical predictions. (c) 2006 American Institute of Physics.