Microwave spectrum and molecular structure of the HSC radical

The HSC radical, that is a geometrical isomer of the HCS radical, has been identified and characterized by microwave spectroscopy. The HSC radical has been produced in a discharge plasma of a gaseous mixture of H2S and CO, an d its rotational spectral lines are observed with a source-modulation spect rometer and a Fourier-transform millimeter-wave spectrometer. The spectrum of the deuterated species, DSC, has also been measured with a source-modula tion spectrometer. Rotational constants, centrifugal distortion constants, and spin-rotation interaction constants with their centrifugal distortion c orrections for HSC and DSC are determined from the observed transition freq uencies by a least-squares method. Furthermore hyperfine interaction consta nts of the hydrogen nucleus are also determined for HSC. The Fermi contact term of the hydrogen nucleus takes a large positive value, 288.845 +/- 0.18 5 MHz, which indicates that the HSC radical is a sigma radical ((2)A') in t he ground electronic state. The harmonic force field is evaluated from the obtained centrifugal distortion constants and inertial defects. The zero-po int vibrational average structure is determined as follows; r(z)(H-S)=1.390 +/- 0.003 Angstrom, r(z)(S-C)=1.6403 +/- 0.0005 Angstrom and alpha(z)(HSC) =104.2 +/- 0.2 degrees. (C) 2000 American Institute of Physics. [S0021-9606 (00)01324-6].