Matrix isolation and ab initio studies of 1 : 1 hydrogen-bonded complexes HCN-H2O and HNC-H2O produced by photolysis of formaldoxime

The products of 193 nm photolysis of formaldoxime (CH2NOH) are studied in s olid argon at 17 K. Four species are experimentally found to appear in the photolysis, and they are identified with the aid of ab initio calculations as different HCN/HNC-water complexes: NCH ... OH2, HCN ... HOH, CNH ... OH2 , and HNC ... HOH. The HNC-water complexes are experimentally observed for the first time. Computationally, the NCH ... OH2 complex possesses the lowe st energy and the HCN ... HOH complex is 5.3 kJ mol(-1) higher in energy. T he two HNC-water complexes are 60-70 kJ mol(-1) higher in energy than the H CN-water complexes. The CNH ... OH2 is calculated to be the strongest compl ex with an interaction energy of about -30 kJ mol(-1). The barrier separati ng the HCN/HNC systems is high enough to prevent interconversion between th em by IR pumping of the fundamental vibrations. On the other hand, rearrang ement inside the two chemical systems is achievable with selective IR excit ation of the OH, CH, and NH stretching vibrations.