HYDROGEN-BONDED COMPLEXES OF HCL WITH CO, C2H2, C2H4, PH3, H2S, HCN, H2O AND NH3 - CORRELATED QUANTUM CHEMICAL CALCULATIONS OF GEOMETRIES, ENERGETICS, VIBRATIONAL FREQUENCIES AND CL-35 QUADRUPOLE COUPLING-CONSTANTS

The results of ab initio quantum chemical calculations carried out using the MP2 perturbation and averaged coupled pair functional (ACPF) methods are reported on hydrogen bonded binary complexes of HCI with CO, C2H2, C2H4, PH3, H2S, HCN, H2O and NH3. The geometries, vibrational frequencies and related quantities such as zero point vibrational energies, librational amplitudes, infrared intensities, etc., have been computed at the MP2 level, while the ACPF method has been used to obtain electric field gradients, dipole moments and also dissociation energies. The theoretical predictions of geometries, intermolecular stretching frequencies, librational amplitudes and Cl-35 nuclear quadrupole coupling constants are in good agreement with the corresponding experimental data. The effects of basis set superposition have been found to be significant in the case of the dissociation energies. Exploratory calculations on the NH3 ... HCl complex, using atomic natural orbital (ANO) bases, demonstrate, however, that a significant reduction in the superposition error can be achieved with ANO's. The results of coupled cluster calculations, performed also on NH3 ... HCl, indicate that triple excitations can make a substantial contribution to the dispersion energy.