FTIR and ab initio study of the 1/1 complex between water and carbon dioxide in solid nitrogen

Infrared spectra of the 1/1 complex between water and carbon dioxide isolated in a nitrogen matrix are reported. Isotopic substitution of water (HOD, D2O) suggests the existence of two very weak complexes with a nearly T-shaped structure where the C atom is bonded to the water oxygen: one of C2v symmetry and another one of Cs symmetry, in which a slight distortion results in a very weak interaction between one hydrogen atom of water and one oxygen atom of carbon dioxide. This result is supported by force constant calculations, consistent with a double, symmetrical, and unsymmetrical force field, and ab initio calculations. At the MP2/aug-cc-PVTZ level corrected from basis set superposition error the C2v structure is a saddle point with an imaginary frequency for H2O rocking, in contrast to a Cs structure, which would have nonequivalent hydrogen atoms. Nevertheless, the energies of both structures, with a stabilization energy of 1.97 kcal mol-1, differ by less than 0.01 kcal mol-1 from each other. A comparison of calculated and observed frequency shifts allows us to suggest the presence in the matrix of both C2v and Cs complexes.