Electronic spectroscopy of the (A)over-tilde (1)A ''(') - (X)over-tilde (1)A ' system of CDBr

摘要

We report fluorescence excitation and single vibronic level emission spectra of jet-cooled CDBr in the 450-750 nm region. A total of 32 cold bands involving the pure bending levels 2(0)(n) with n=3-10 and combination bands 2(0)(n)3(0)(1) (n=2-10), 2(0)(n)3(0)(2) (n=2-9), 1(0)(1)2(0)(n) (n=7-10), and 1(0)(1)2(0)(n)3(0)(1) (n=6,8-9) in the A (1)A(')<- X (1)A(') system of this carbene were observed; most of these are reported and/or rotationally analyzed here for the first time. Rotational analysis yielded band origins and effective (B) rotational constants for both bromine isotopomers ((CDBr)-Br-79 and (CDBr)-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-D stretching frequency (2350 cm(-1)) is determined for the first time, in excellent agreement with theory, as are the Br-79-Br-81 isotope splittings in the excited state. Our emission spectra probe the vibrational structure of the X (1)A(') and a (3)A(') states up to similar to 9000 cm(-1) above the vibrationless level of the X (1)A(') state; the total number of levels observed is around twice that previously reported. Unlike CHBr, where even the lowest bending levels are perturbed by spin-orbit interaction with the triplet origin, the term energy of every level save one below 3000 cm(-1) in CDBr is reproduced by a Dunham expansion to within a standard deviation of 1 cm(-1), and a spin-orbit coupling matrix element of similar to 330 cm(-1) is derived from a deperturbation analysis of the triplet origin. The multireference configuration interaction (MRCI) calculations of Yu [J. Chem. Phys. 115, 5433 (2001)] well reproduce triplet perturbations in the pure bending manifold, and 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.