Microwave spectrum and molecular structure of the HS2 radical

Rotational spectral lines of the HS2 and DS2 radicals in the 2A″ ground electronic state are detected by a source-modulation microwave spectrometer combined with a free-space cell. The HS2 radical is produced in the cell by discharging a pure H2S gas. The spectrum of DS2 is observed by using a mixture of H2S and D2. The rotational constants, the centrifugal distortion constants, the spin-rotation interaction constants with their centrifugal distortion corrections, and the hyperfine interaction constants for the hydrogen nucleus are determined by least-squares analyses. The harmonic force constants are evaluated from the observed centrifugal distortion constants in combination with the vibrational frequencies reported previously. The zero-point average structure of HS2 is determined from the observed rotational constants of HS2 and DS2 with the aid of the harmonic force constants: rz(S—S) = 1.9650 (7) Å, rz (S—H) = 1.362 (3) Å, and αz (HSS) = 101/7 (4)° (1 Å = 10−10 m). The equilibrium distances for the S—S and S—H bonds are derived to be 1.9606 (7) Å and 1.352 (3) Å, respectively, by assuming the anharmonic constants of the corresponding diatomic molecules.