Theoretical predictions of vibration-rotation-tunneling dynamics of the weakly bound trimer (H2O)(2)HCl

In this Letter we report a theoretical study of the vibration-rotation-tunn eling (VRT) states of the (H2O)(2)HCl trimer. Five degrees of freedom are c onsidered: two angles corresponding to the torsional (flipping) motions of the free, non-hydrogen-bonded, hydrogen atoms in the complex, and three ang les describing the overall rotation of the trimer in the space. A two-dimen sional potential energy surface is generated ab initio by symmetry-adapted perturbation theory (SAPT). Tunneling splittings, frequencies of the interm olecular vibrations, and vibrational line strengths of spectroscopic transi tions are predicted. (C) 2001 Elsevier Science B.V. All rights reserved.