Protonated hydrochlorous acid (HOClH+): Molecular structure, vibrational frequencies, and proton affinity

Protonated hydrochlorous acid (HOClH+) has been examined theoretically. Equilibrium geometries have been optimized and harmonic vibrational frequencies obtained for each of the parent and protonated structures at various levels of theory employing second-order Mo/ller–Plesset perturbation interaction theory (MP2), singles and doubles excitation configuration interaction theory (CISD), and coupled-cluster theory (CCSD). Our study has found that protonation of the oxygen of HOCl is favored over protonation at the chlorine site. Protonation of the oxygen leads to a pyramidal structure of Cs symmetry. There is a planar Cs structure which is the inversion transition state. The inversion barrier is 3.2 kcal mol−1. The proton affinity of hypochlorous acid, HOCl, is found to be 153.1 kcal mol−1 at 0 K.