Pseudorotation tunneling in several water trimer isotopomers

The tunneling dynamics of several water trimer isotopomers is investigated by using an extension of the Hamiltonian that was previously derived for pu re (more symmetric) trimers. This Hamiltonian takes into account the overal l rotation of the trimer and three internal, torsional, or pseudorotational , motions of the monomers. Quantitative calculations of the torsional level s are presented, and the small effects of internal, i.e., hydrogen bonded, H/D substitutions and the much larger effects of external H/D substitutions are discussed. Transition line strengths are computed as well, and the ass ignment of most of the bands observed for the various water trimer isotopom ers is confirmed. In one case we suggest a different assignment. (C) 1999 A merican Institute of Physics. [S0021-9606(99)03501-1].