The b1Σ+(b0+) → X3Σ−(X10+, X21) and a1Δ(a2) → X3Σ−(X21) transitions of SeS

Emission spectra of SeS in the near-infrared spectral region have been measured with a high-resolution Fourier-transform spectrometer. The SeS molecules were generated in a fast-flow system by heating SeS2 in a flow of Ar carrier gas and were excited by electronic-to-electronic energy transfer from metastable singlet oxygen O2(a1Δg). The b1Σ+(b0+) → X3Σ−(X10+, X21) transitions of SeS were reinvestigated at high spectral resolution. Spectra of the weak 0-0 band of the b0+ → X21 sub-system comprising electric and magnetic dipole branches are presented and compared with computer simulations. New weak emissions near 4 060 cm−1 are assigned to the 0-0 and 1-1 bands of the hitherto unknown a1Δ(a2) → X3Σ−(X21) transition of SeS. By comparing the bandshape of the 0-0 band with a computer simulation, the following spectroscopic constants of the a1Δ(a2) state of SeS were derived (in cm−1): T0 = 4 057.75(5), B0 = 0.1765(2) where the numbers in parentheses are estimated error limits of the parameters in units of the last digit. From the separation of the 0-0 and 1-1 bands and the known vibrational spacing in the X2 state, ΔG1/2(a) = 529.4(10) cm−1 has been derived.