Département de chimie moléculaire

Structural, energetic, and spectroscopic properties of the hydrogen chloride trihydrate (H2O)3HCl have been calcd. by ab initio and d. functional methods. The stationary points on the potential energy surface and the harmonic frequencies were obtained with the d. functional theory, the second-order Moller-Plesset theory, and the self-consistent reaction field theory, while the corresponding interaction energies and binding energies were computed using the coupled-cluster method restricted to single, double, and noniterative triple excitations. The origins of the bonding have been characterized by symmetry-adapted perturbation theory of pair and three-body interactions. The global min. on the potential energy surface of the cluster corresponds to a cyclic structure with the water and hydrogen chloride mols. connected by hydrogen bonds. Another min., corresponding to an ionic form of the trihydrate, (H2O)2H3O+Cl-, has a binding energy only ≈2 kcal/mol higher than the global min., but it is sepd. by a large barrier. The pathway connecting the two min. has been found, and the structure of the corresponding transition state has been detd. The geometry of the ionic min. agrees well with the crystal structure of the hydrogen chloride trihydrate from single-crystal X-ray diffraction studies. Also, the computed harmonic frequencies and their theor. assignment are in agreement with the exptl. data recorded in the gas phase in argon matrixes and in the cryst. phase. [on SciFinder(R)]