MATRIX-ISOLATION INFRARED-SPECTROSCOPY AND DFT CALCULATIONS OF COMPLEXES BETWEEN WATER AND NITROGEN

The mid-infrared spectra of water-nitrogen mixtures in argon matrices have been investigated. Evidence for the existence of several (H2O)(m) (N-2)(n), or m:n, complexes has been obtained from the appearance of m any absorptions in the nu OH, nu NN and delta OH spectral regions whic h are not present in the spectra of H2O/Ar binary matrices. Concentrat ion effects allow identification of the four (seven) intramolecular fu ndamentals of the 1:1 (2:1) species. The structural properties of thes e two complexes are discussed on the basis of ab initio calculations c arried out within the framework of the density functional theory (DFT) . The comparison of the calculated and observed vibrational properties of the 1:1 complex does not allow us to confidently deduce its struct ure because of the weakness of the perturbations. In the case of the 2 :1 heterotrimer it is clearly established that the nitrogen molecule i s fixed on the proton acceptor molecule of (H2O)(2), in a hydrogen-bon d type interaction. The frequency shifts with respect to the water dim er are accounted for in terms of cooperative effects. (C) 1998 Elsevie r Science B.V. All rights reserved.