TUNNELING DYNAMICS, SYMMETRY, AND FAR-INFRARED SPECTRUM OF THE ROTATING WATER TRIMER .2. CALCULATIONS AND EXPERIMENTS

With the Hamiltonian derived in the preceding paper and the ab initio potentials of T. Burgi, S. Graf, S. Leutwyler, and W. Klopper [J. Chem . Phys. 103, 1077 (1995)] and of J. G. C. M. van Duijneveldt-van de Ri jdt and F. B. van Duijneveldt [Chem. Phys. Lett. 237, 560 (1995)], we calculate the pseudo-rotation tunneling levels in a rotating water tri mer. The internal motions are treated by a three-dimensional discrete variable representation and the Coriolis coupling with the overall rot ation is included. Also the effects of donor tunneling are included, b y introducing semi-empirical coupling matrix elements. New experimenta l data are presented for the c-type band at 87.1 cm(-1) in (H2O)(3), w hich show that specific levels in the donor tunneling quartets of this band are further split into doublers. With the results of our quantit ative calculations and the model of the preceding paper we can underst and the mechanisms of all the splittings observed in the earlier high- resolution spectra of (H2O)(3) and (D2O)(3), as well as these new spli ttings, in terms of pseudo-rotation tunneling, donor tunneling and Cor iolis coupling. An unambiguous assignment is given of all the bands ob served and analyzed. The ab initio potential of the Van Duijneveldts y ields accurate energies of the lower pseudo-rotation levels, the poten tial of Burgi ct al. performs better for the higher levels. With our a nalysis we can deduce from the spectra that donor tunneling involves i nversion of the trimer. (C) 1996 American Institute of Physics.