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

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Abstract
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.