Ab initio calculations on SnCl₂and Franck-Condon factor simulations of its ã-X˜ and B˜-X˜ absorption and single-vibronic-level emission spectra

Abstract

Minimum-energy geometries, harmonic vibrational frequencies, and relative electronic energies of some low-lying singlet and triplet electronic states of stannous dichloride, SnCl₂, 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 X˜¹A₁, ã³B₁, and B˜¹B₁ states of SnCl₂have been computed and used to calculate anharmonic vibrational wave functions of these three electronic states. Franck-Condon factors between the X˜¹A₁ state, and the ã³B₁and B˜ ¹B₁ states of SnCl₂, which include anharmonicity and Duschinsky rotation, were then computed, and used to simulate the ã-X˜ and B˜-X˜ absorption and corresponding single-vibronic-level emission spectra of SnCl₂which are yet to be recorded. It is anticipated that these simulated spectra will assist spectroscopic identification of gaseous SnCl₂in the laboratory and/or will be valuable in in situ monitoring of SnCl₂in the chemical vapor deposition of SnO₂thin 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.