A restricted active space self-consistent field and multireference configuration interaction study of the lifetime of the A 3Π state of SO

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Abstract
Ab initio methods were applied to compute the potential curves for the X 3Σ− and A 3Π states, the transition dipole moment, and the radiative lifetimes of the vibrational levels of the A state of the SO molecule. Extended atomic natural orbital basis sets including up to g‐type functions were used. The potential energy curves were computed at the multireference configuration interaction level of approximation. The calculated bond distances and bond energies are 1.498 (1.481) Å and 5.21 (5.36) eV, respectively, for the X state, and 1.694 (1.609) Å and 0.57 (0.64) eV, respectively, for the A state (experimental values within parentheses). Restricted active space self‐consistent field (RASSCF) wave functions were used to obtain the transition dipole moments, and the size of the RASSCF active orbital space was increased until stability of the transition moment value was achieved. The calculated transition moment strongly depends on the internuclear distance. The calculated value of the A 3Π, v=0 lifetime is 46.6 μs, while the experimental values are in the range of 36–39 μs. The computed lifetime is a very sensitive function of the relative accuracy of the potential energy and transition moment curves: for example, removing the g‐type function on sulphur increases the lifetime to 55 μs.

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