Fourier transform millimeter-wave spectroscopy of the HCS radical in the A′2 ground electronic state

The 101–000 rotational transition of the HCS radical in the X̃ A′2 ground electronic state has been observed with a Fourier transform millimeter-wave spectrometer in combination with a pulsed discharge nozzle. The radical is produced by discharging a mixture of CH4 and H2S diluted in Ar. Six fine and hyperfine components are detected, and the effective rotational constant, spin–rotation interaction constant, and hyperfine interaction constants are determined accurately. The Fermi contact term of the hydrogen nucleus is found to be much smaller than that for the isovalent radical, HCO, indicating that the HCS radical is more close to a linear structure than the HCO radical.