Franck-Condon Simulations including Anharmonicity of the (A)over-tilde1A"-(X)over-tilde1A′ Absorption and Single Vibronic Level Emission Spectra of HSiCl and DSiCl

RCCSD(T) and/or CASSCF/MRCI calculations have been carried out on the (X) over tilde (1)A' and (A) over tilde (1)A '' 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 the (A) over tilde (1)A '' <- (X) over tilde (1)A' absorption and (A) over tilde (1)A '' -> (X) over tilde (1)A' single vibronic level (SVL) emission spectra of HSiCl and DSiCl. Simulated absorption and experimental LIF spectra, and simulated and observed (A) over tilde (1)A ''(0,0,0) -> (X) over tilde (1)A' emission spectra, of HSiCl and DSiCl are in very good agreement. However, agreement between simulated and observed (A) over tilde (1)A ''(0,1,0) -> (X) over tilde (1)A' and (A) over tilde (1)A ''(0,2,1) -> (X) over tilde (1)A' SVL emission spectra of DSiCl is not as good. Preliminary calculations on low-lying excited states of HSO suggest that vibronic interaction between low-lying vibrational levels of the (A) over tilde (1)A '' state and highly excited vibrational levels of the (a) over tilde (3)A '' is possible. Such vibronic interaction may change the character of the low-lying vibrational levels of the (A) over tilde (1)A '' state, which would lead to perturbation in the SVL emission spectra from these vibrational levels.