Microwave and tunable far-infrared laser spectroscopy of OCH 2O: investigation of the water tunneling potential

Abstract

The K p =O → 1 rotation—tunneling bands of O 12CH 2O and O 12CD 2O have been measured in the region between 400 and 600 GHz. Two bands for each isotopomer were observed corresponding to Δ 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) = 2ν t, where ν t is the tunneling splitting. We obtain tunneling splitting of 16.684 GHz for O 12CH 2O and 1.012 GHz for O 12CD 2O. These measurements are in good agreement with the predictions of Yaron (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.