MICROWAVE AND TUNABLE FAR-INFRARED LASER SPECTROSCOPY OF OC-H2O - INVESTIGATION OF THE WATER TUNNELING POTENTIAL

The K(p) = 0 --> 1 rotation-tunneling bands of (OC-H2O)-C-12) and (OC-D2O)C-12 have been measured in the region between 400 and 600 GHz. Two bands for each isotopomer were observed corresponding to DELTA-K(p) = 1, b-type rotational transitions in the A and B water tunneling states. Each band was fit independently using a Watson A-reduced Hamiltonian yielding all three rotational and several distortion constants per band. The effective A-rotational constants, A*, contain a contribution due to water tunneling. Assuming the tunneling splittings are the same in K(p) = 0 and K(p) = 1, A*(A state)-A*(B state) = 2v(t), where v(t) is the tunneling splitting. We obtain tunneling splittings of 16.684 GHz for (OC-H2O)-C-12 and 1.012 GHz for (OC-D2O)-C-12. These measurements are in good agreement with the predictions of Yaron et al. (J. Chem. Phys. 92 (1990) 7095). Effective one-dimensional potentials have been employed to place constraints on the hydrogen bond geometry, to model the measured tunneling splittings, and to predict higher frequency vibration-rotation-tunneling transitions.