A theoretical study of the spectroscopic properties of the ground and first excited electronic state of HS2

Accurate thermochemical and spectroscopic properties have been calculated for the X∼2A″ and A∼2A′ electronic states of the HS2 radical using highly correlated coupled cluster methods with explicit basis set extrapolations. The heat of formation of HS2 at 0 K is predicted to be 26.1 kcal/mol based in part on accurate benchmark calculations of SH and S2. The equilibrium geometry of HS2, which is estimated to be accurate to at least 0.002 Å, is predicted to be re(SH) = 1.3482 Å, Re(SS) = 1.9608 Å, and θe(HSS) = 101.52°. In addition to a set of centrifugal distortion constants, harmonic frequencies, and vibration-rotation coupling constants being calculated for both electronic states of HS2 and DS2 using second order perturbation theory, the anharmonic infrared band origins and A∼-X∼ emission spectra were calculated variationally together with their intensities. These made use of accurate three-dimensional, near-equilibrium potential energy and dipole moment functions. The ν3 fundamentals of both HS2 and DS2 are reproduced to better than 3 cm−1. Predictions are made for both the ground state infrared spectrum as well as the electronic spectrum. Two possible misassignments in the recently reported chemiluminescence spectra are noted.