Matrix isolation infrared spectroscopy and DFT calculations of complexes between water and nitrogen

Abstract The mid-infrared spectra of water–nitrogen mixtures in argon matrices have been investigated. Evidence for the existence of several (H 2 O) m (N 2 ) n , or m : n , complexes has been obtained from the appearance of many absorptions in the ν OH, ν NN and δ OH spectral regions which are not present in the spectra of H 2 O/Ar binary matrices. Concentration effects allow identification of the four (seven) intramolecular fundamentals of the 1:1 (2:1) species. The structural properties of these two complexes are discussed on the basis of ab initio calculations carried 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 structure because of the weakness of the perturbations. In the case of the 2:1 heterotrimer it is clearly established that the nitrogen molecule is fixed on the proton acceptor molecule of (H 2 O) 2 , in a hydrogen-bond type interaction. The frequency shifts with respect to the water dimer are accounted for in terms of cooperative effects.