Infrared matrix isolation and theoretical studies of the hydrogen bonded complexes between nitrous acid and 1,1-dichloroethylene

The optimization and spectral characteristics of the studied systems were carried out at the MP2 level of theory with 6-311++G(2d,2p) basis set. The performed calculations resulted in five stationary points on the PES for both trans and cis-HONO complexes. Two complexes are stabilized by the O-H⋯π bond, the other two by the O-H⋯Cl bond and one complex by the bifurcated, asymmetric Cl⋯H⋯Cl interaction. In one of the two complexes stabilized by the O-H⋯Cl hydrogen bond an additional C-H⋯O (for cis-HONO) or C-H⋯N (for trans-HONO) hydrogen bond also exists. The topological analysis of the distribution of the charge density by help of AIM theory confirmed the asymmetry of the Cl⋯H⋯Cl bifurcated hydrogen bond and the double O-H⋯Cl and C-H⋯O(N) interaction in one of the five structures. The values of the ρb and ∇2ρb indicate that the Cl⋯H⋯Cl bond is more asymmetric in the cis-HONO complex than in the trans-HONO one. The comparison of the experimental frequencies with the calculated ones for the five structures indicates that the trans- or cis-HONO complexes trapped in the matrixes correspond to the structures stabilized by the O-H⋯π bond or by the O-H⋯Cl bond.