Ab initio calculations on Sn Cl2 and Franck-Condon factor simulations of its ã - X̃ and B̃ - X̃ absorption and single-vibronic-level emission spectra

Minimum-energy geometries, harmonic vibrational frequencies, and relative electronic energies of some low-lying singlet and triplet electronic states of stannous dichloride, Sn Cl2, have been computed employing the complete-active-space self-consistent-field/multireference configuration interaction (CASSCF/MRCI) and/or restricted-spin coupled-cluster single-double plus perturbative triple excitations [RCCSD(T)] methods. The small core relativistic effective core potential, ECP28MDF, was used for Sn in these calculations, together with valence basis sets of up to augmented correlation-consistent polarized-valence quintuple-zeta (aug-cc-pV5Z) quality. Effects of outer core electron correlation on computed geometrical parameters have been investigated, and contributions of off-diagonal spin-orbit interaction to relative electronic energies have been calculated. In addition, RCCSD(T) or CASSCF/MRCI potential energy functions of the X̃ A11, ã B13, and B̃ B11 states of Sn Cl2 have been computed and used to calculate anharmonic vibrational wave functions of these three electronic states. Franck-Condon factors between the X̃ A11 state, and the ã B13 and B̃ B11 states of Sn Cl2, which include anharmonicity and Duschinsky rotation, were then computed, and used to simulate the ã - X̃ and B̃ - X̃ absorption and corresponding single-vibronic-level emission spectra of Sn Cl2 which are yet to be recorded. It is anticipated that these simulated spectra will assist spectroscopic identification of gaseous Sn Cl2 in the laboratory and/or will be valuable in in situ monitoring of Sn Cl2 in the chemical vapor deposition of Sn O2 thin films in the semiconductor gas sensor industry by laser induced fluorescence and/or ultraviolet absorption spectroscopy, when a chloride-containing tin compound, such as tin dichloride or dimethyldichlorotin, is used as the tin precursor.