Nuclear hyperfine interaction of rotating hydrogen: A spectroscopic investigation of hydrogen-OCS van der Waals complexes.

The rotational spectra of five weakly bonded hydrogen-OCS complexes (paraH₂, orthoH₂, HD, orthoD₂, and paraD₂) are measured. Hyperfine structure is resolved and analyzed in all except the complex with paraH₂, where I=0. For the two j=1 species, orthoH₂-OCS and paraD₂-OCS, nuclear hyperfine coupling constants are found to be d_a=21.2(2) and 8.4(2) kHz, respectively, indicative of nearly free uniaxial rotation of the hydrogen around the b-inertial axis. Similar analyses for HD-OCS and orthoD₂-OCS yield the quadrupole coupling constants eqQ_a=16(2) and 30(2) kHz, respectively, showing that the internal rotational motions of HD and orthoD₂ in the complex are slightly hindered producing a small nonspherical distribution. For orthoD₂-OCS, the observed hyperfine structure indicates that the nuclear spin states I=0 and 2 are strongly coupled in the rotation of the complex. [ABSTRACT FROM AUTHOR]