Infrared emission spectroscopy of the A4Φi-X4Δi and B4Πi-X4Δi transitions of CoS

The near-infrared emission spectrum of CoS has been recorded at a resolution of 0.04 cm−1 using a Fourier transform spectrometer. Gas-phase CoS was produced by the reaction of cobalt vapor and CS2 vapor at about 3000 K in a carbon tube furnace. Two electronic transitions were observed for the first time in the 3200-6000 cm−1 region and have been assigned to the A4Φi-X4Δi and B4Πi-X4Δi transitions. The 0-0 bands for all four sub-bands of the A4Φi-X4Δi transition, and the 0-0, 0-1, 1-0, and 1-1 bands for the 5/2-7/2 sub-band of the B4Πi-X4Δi transition were rotationally analyzed. Combined with the previous microwave data from the literature, the present data were fitted using the usual Hund's case (c) energy level expressions, and spectroscopic constants were obtained for the X4Δi, A4Φi, and B4Πi states of CoS. A Hund's case (a) fit was also carried out for the A4Φi-X4Δi transition. The presence of a low-lying 4Φi state for both CoS and CoO was not anticipated based on previous experimental and theoretical work.