PROTON-DONOR PROPERTIES OF WATER AND AMMONIA IN VANDERWAALS COMPLEXES- BE-H2O AND BE-NH3

The potential energy surfaces (PES) of Be-H2O and Be-NH3 are studied w ith particular attention to characterization of proton-donor propertie s of water and ammonia. Calculations were performed by means of both s upermolecular and intermolecular Moller Plesset perturbation theory. T he Be-H2O PES reveals two van der Waals minima: the C2v minimum (D(e) = 176 em-1, R(e) = 6.5 bohr), and the H-bonded minimum (D(e) = 161 cm- 1, R(e) = 7.5 bohr), separated by a barrier of 43 cm-1 at the T-shaped configuration. The Be-NH3 PES reveals only one van der Waals minimum, at the C3v configuration (D(e) = 260 cm-1, R(e) = 6.5 bohr) and a sad dle point at the H-bonded geometry. The locations of the minima as wel l as the anisotropy of the interaction are determined by the anisotrop y of electric polarization contribution, embodied by the self-consiste nt-field (SCF)-deformation and perturbation induction energies.