Franck-condon simulations including anharmonicity of the ã¹a″-x̃¹á absorption and single vibronic level emission spectra of HSiCl and DSiCl

RCCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X̃1Á and Ã1A″ states of HSiCl employing basis sets of up to the aug-cc-pV5Z quality. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HSiCl. Franck-Condon factors which include allowance for anharmonicity and Duschinsky rotation between these two states of HSiCl and DSiCl were calculated employing RCCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate theà 1A″ ← X̃1Á absorption and Ã1A″ → X̃1Á single vibronic level (SVL) emission spectra of HSiCl and DSiCl. Simulated absorption and experimental LIF spectra, and simulated and observed Ã1A″ (0,0,0) → X̃1Á SVL emission spectra, of HSiCl and DSiCl are in very good agreement. However, agreement between simulated and observed Ã1A″(0,1,0) → X̃1Á and Ã1A″(0,2,1) → X̃1Á SVL emission spectra of DSiCl is not as good. Preliminary calculations on low-lying excited states of HSiCl suggest that vibronic interaction between low-lying vibrational levels of the Ã1A″ state and highly excited vibrational levels of the ã3A′ is possible. Such vibronic interaction may change the character of the low-lying vibrational levels of the Ã1A″ state, which would lead to perturbation in the SVL emission spectra from these vibrational levels.