HYPERFINE AND TUNNELING EFFECTS IN THE MICROWAVE-SPECTRUM OF N-2-OCS

A- and b-type rotational transitions of N-2-OCS between 6 and 18 GHz h ave been recorded using a pulsed, supersonic nozzle, Fourier-transform microwave spectrometer. The rotational spectrum is indicative of a pl anar, T-shaped complex, with the nitrogen molecular axis oriented towa rd the carbon of OCS. Symmetry effects in the nuclear quadrupole hyper fine structure imply that the nitrogen nuclei are effectively equivale nt due to rotation of the nitrogen molecule. The resulting symmetric a nd antisymmetric combined nuclear spin and tunneling states are associ ated with slightly different rotational and hyperfine parameters. Firs t-order quadrupole and spin-rotation interactions are used to fit the hyperfine structure, and the hyperfine dependence on rotational state is investigated. An instance of accidental near-degeneracy has allowed determination of the chi(ab) off-diagonal quadrupole coupling constan t for the symmetric state. Deduced structural parameters have been com pared with a model based on distributed multipole, dispersion, and har d sphere interactions. The quadrupole coupling constants of the two tu nneling symmetry states have been used to model the angular tunneling potential, giving a barrier to rotation of 40.44 cm(-1) and a tunnelin g frequency of 2450.0 GHz. (C) 1996 Academic Press, Inc.