3-DIMENSIONAL MODEL CALCULATION OF TORSIONAL LEVELS OF (H2O)(3) AND (D2O)(3)

A coupled three-dimensional model calculation of the low-frequency lar ge-amplitude intermolecular torsional states in (H2O)(3) and (D2O)(3) is presented, based on the analytical modEPEN intermolecular potential surface and a three-dimensional discrete variable representation appr oach. The lowest torsional levels of both (H2O)(3) and (D2O)(3) lie ab ove the sixfold (upd) torsional barrier. The first eight (eleven) tors ions of (H2O)(3) ((D2O)(3)) are pseudorotational states. The 'radial' and 'polar' torsional fundamental frequencies are predicted at 151 and 160 cm(-1) for (D2O)(3), and for (H2O)(3) at 185.0 and 185.3 cm(-1) r espectively. Each of these in turn support a ladder of pseudorotationa l levels.