IS (NH3)2 HYDROGEN-BONDED

Vibration-rotation-tunneling (VRT) splittings have been computed for t he dimer (NH3)2 by the use of four different model potentials. The six -dimensional nuclear motion problem is solved variationally in a symme try adapted basis consisting of analytic radial functions and rigid ro tor functions depending on the five internal angles, as well as on the three overall rotation angles. Two of the potentials are designed suc h that they have no barrier for interchange tunneling and the other tw o potentials have barriers of 31.1 and 24.4 cm-1, respectively. The to p of the barrier corresponds to a cyclic structure and the two equival ent minima on either side of the barrier to nearly linear hydrogen bon ds. Energy splittings, dipole moments, nuclear quadrupole splittings, and the amount of quenching of the monomer umbrella inversions are com puted and compared with the available experimental numbers. The potent ial that gives best agreement with the observed quantities has an equi librium hydrogen bonded structure close to linear, but a VRT-averaged ground state structure that is nearly cyclic.