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 solid 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 lowest energy and the HCN···HOH complex is 5.3 kJ mol-1 higher in energy. The two HNC−water complexes are 60−70 kJ mol-1 higher in energy than the HCN−water complexes. The CNH···OH2 is calculated to be the strongest complex with an interaction energy of about −30 kJ mol-1. The barrier separating the HCN/HNC systems is high enough to prevent interconversion between them by IR pumping of the fundamental vibrations. On the other hand, rearrangement inside the two chemical systems is achievable with selective IR excitation of the OH, CH, and NH stretching vibrations.