Fluorescence excitation and emission spectroscopy of the ÃA″1←X̃A′1 system of CHBr

Abstract

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 (79)Br,CH (81)Br). The derived A (1)A(") vibrational intervals are combined with results of [Yu et al. 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 (79)Br-(81)Br 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 approximately 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 et al. 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.