Complexes pairing hypohalous acids with nitrosyl hydride. blue shift of a NH bond that is uninvolved in a H-bond

Correlated calculations are used to analyze the interaction between nitrosyl hydride (HNO) and hypohalous acids (HOF, HOCl, and HOBr). Two minima are located on the potential energy surface of each complex, in both of which HOX acts as proton donor. Donation to the N atom of HNO makes for a more strongly bound complex, as compared to the OH..O bond in the secondary minimum. Binding energies of the global minimum are about 22 kJ/mol, as compared to 18 kJ/mol for the secondary structure; there is little sensitivity to the identity of the halogen atom. Whereas the covalent OH bond of HOX stretches and shifts to the red upon complexation, the NH bond of HNO, whether involved in a H-bond or not, behaves in the opposite manner.