Ab initio SCF and CI study of the ground and first excited state of the HSO radical

Abstract

Potential surfaces for all three internal coordinates of the HSO radical in both its ground ( 2A″) and first excited ( 2A′) state have been calculated using ab initio SCF and CI methods. The T o value for the transition between these two electronic states is calculated to be 1.56 eV compared to the observed result of 1.778 eV. The half-life for this process is calculated to be 21 ms using the dipole length operator (a value of 7 ms is obtained when the generally less reliable dipole velocity is employed). In agreement with experiment the most probable vibrational transitions are calculated to be 1 ← 0 for SO stretch and 0 ← 0 for both the bending and SH stretching modes. The SO bond length in the best treatment employed is 2.91 bohr in the ground state compared to 3.22 bohr for the 2A′ species, while much smaller changes are indicated for the other two coordinates upon exciation (100° vs 95° for internuclear angle and 2.55 bohr vs 2.53 bohr for the SH bond length). At the calculated ground state geometry the dipole moments of the lower and upper states are predicted to be 2.27 and 1.78 D respectively, with an O → S charge transfer indicated to occur as a result of the excitation process.