Spectroscopic and Theoretical Studies of the Complexes between Nitrous Acid and Ammonia

The complexes formed between cis - and trans -HONO isomers and ammonia have been observed and characterized in argon matrices. Five perturbed HONO vibrations and one perturbed NH 3 deformation vibration were identified for the H 3 N···HONO- trans complex, and one perturbed HONO vibration and perturbed NH 3 deformation vibration were identified for the H 3 N···HONO- cis complex. The OH stretching vibration in the H 3 N···HONO- trans complex is ca. 800 cm -1 red-shifted and NOH bending vibration is ca. 190 cm -1 blue-shifted with respect to the trans -HONO monomer, indicating formation of a very strong molecular hydrogen bond. Theoretical studies of the structure and spectral characteristics of the H 3 N···HONO- trans and H 3 N··· HONO- cis complexes were carried out on the electron correlation level and G-311+G(2df,2pd) basis set. The calculated binding energy at the MP2 level is −40.13 and −36.39 kJ mol -1 for the H 3 N···HONO- trans and H 3 N···HONO- cis complexes, respectively. The calculated spectra reproduce very well the frequencies and the intensities of the measured spectra.