Fluorescence excitation and emission spectroscopy of the A-tilde~1A' -X-tilde~1A' system of CHBr

摘要

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~n_0 with n = 2-8 and combination bands 2_0~n3_0~1(n=l_-8),2_0~n3_0~2(n=1-6),2_0~n3_0~3(n=1-2),1_0~12_0~n(n=5-7),1_0~12_0~n3_0~1(n=4-6),and 1_0~12_0~n3_0~2(n = 5) in the A-tilde<- X-tilde~1A' 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-tilde~1A" 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~n3~1,and 2~n3~2 progressions.The A-tilde~1A" state C-H stretching frequency is determined here for the first time,and the observed v_3 dependence of the ~(79)Br-~(81)Br isotope splitting in the A-tilde~1A" state is in good agreement with theoretical expectations.Our dispersed fluorescence spectra probe the vibrational structure of the X-tilde~1A' state up to approx 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-tilde~3A" 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-tilde~1A' C-H stretching fundamental.Globally,the vibrational frequencies of X-tilde~1A',a-tilde~3A",and A-tilde~1A" are in excellent agreement with theoretical predictions.