Calculation of the vibronic structure of the photodetachment spectra of CCCl̄ and CCBr̄

The vibronic structure of the closely spaced and strongly coupled X̃ +2 and à Π2 states in the photodetachment spectra of CC Cl- and CC Br- has been calculated by considering -Π vibronic coupling together with spin-orbit coupling. The stretching modes are treated within the so-called linear-vibronic-coupling model. The vibronic and spin-orbit parameters have been determined by accurate ab initio electronic-structure calculations. While the nonrelativistic vibronic-coupling parameters are of approximately equal strength in CCCl and CCBr, the vibronic-coupling parameters of spin-orbit origin are found to be larger in the latter. The calculated photodetachment spectra of both systems are shown to exhibit a complicated vibronic structure due to strong -Π vibronic coupling. The spectral envelopes of the calculated photodetachment spectra exhibit a double-hump reminiscent of strongly coupled E×e Jahn-Teller systems.