Near-Infrared Transitions from the Singlet Excited States to the Ground Triplet State of the S2 Molecule

Intensity of transitions from the b(1)Sigma(+)(g) and a(1)Delta(g) states to the ground state X-3 Sigma(-)(g) in the near IR emission spectrum of the S-2 molecule has been calculated by the multireference configuration interaction method taking into account spin-orbit coupling (SOC). The intensity of the b(1)Sigma(+)(g) - X-3 Sigma(-)(g,Ms=+/- 1) transition is largely determined by the spin interaction with the electromagnetic wave, which comes from the zero-field splitting of the ground X multiplet and the SOC-induced mixing between b and X-3 Sigma(-)(g,0) states. The Einstein coefficients for the experimentally detected 0-0, 0-1, 1-1 bands of the b(1)Sigma(+)(g)-X-3 Sigma(-)(g,Ms=+/- 1) emission system are calculated in good agreement with observations. The Einstein coefficient of the b(1)triangle(g)-X-3 Sigma(-)(g,Ms=+/- 1) magnetic dipole transition is very low, being equal to 0.0014 s(-1). Nonetheless, the weakest of all experimentally observed bands (the 0-0 band of the a-X-Ms=+/- 1 transition) qualitatively corresponds to this calculation. Most importantly, we provide many other IR bands for magnetic dipole b(1)Sigma(+)(g) - X-3 Sigma(-)(g,Ms=+/- 1) and b(1)triangle(g)-X-3 Sigma(-)(g,Ms=+/- 1) transitions, which could be experimentally observable in the S-2 transparency windows from a theoretical point of view. We hope that these results will contribute to the further experimental exploration of the magnetic infrared bands in the S-2 dimer.