Near-infrared Fourier-transform and millimeterwave spectra of the BiS radical

This paper reports the 6400-7400 cm−1 Fourier-transform (FT) near-infrared (NIR) emission spectrum of the BiS X22Π3/2 → X12Π1/2 fine structure bands as well as the millimeterwave rotational spectrum of the X12Π1/2 state. For the FTNIR observations, BiS was produced by reaction of bismuth with sulfur vapor and excited by energy transfer from metastable oxygen, O2(a1Δg), in a fast-flow system. As was the case for BiO [O. Shestakov, R. Breidohr, H. Demes, K.D. Setzer, E.H. Fink, J. Mol. Spectrosc. 190 (1998) 28-77], the 0.5 cm−1resolution spectrum revealed a number of strong bands in the Δv = 0 and ±1 sequences which showed perturbed band spacings, band shapes, and intensities due to avoided crossing of the X22Π3/2 and A14Π3/2 potential curves for v′ ⩾ 4 of X22Π3/2. The millimeterwave rotational spectrum of BiS in its X12Π1/2 state was observed when BiS was produced in a high-temperature oven by a discharge in a mixture of Bi vapor and CS2. The signal to noise ratio was markedly improved by using a White-type multipath cell. Ninety seven features from J′ = 23.5 to J′ = 41.5 were measured between 150 and 300 GHz. Analysis of the 0.5 cm−1 resolution FT spectrum yielded the fine structure splitting and vibrational constants of the states. A simultaneous analysis of millimeterwave and a 0.005 cm−1 FT spectrum of the 0-0 band of the NIR system was carried out to give precise rotational, fine, and hyperfine constants for the X12Π1/2 and X22Π3/2 states. The results are consistent with those reported earlier for BiO and indicate only a slight decrease in the unpaired electron density in the 6p(π∗) orbital on the Bi atom.