Effects of partially quenched orbital angular momentum on the microwave spectrum and magnetic hyperfine splitting in the OH–water complex

The radical complex OH–H2O has been observed by rotational spectroscopy. Spectra for 16OH–16OH2 and 18OH–18OH2 have been analyzed using a two-state model which accounts for nuclear motion on both the 2A′ and 2A″ potential surfaces. Partial quenching of the OH orbital angular momentum dramatically affects the rotational spectra, and the 2A′–2A″ energy separation, ρ, is determined to be −146.50744(42) cm−1. The ground state of the complex has ∼86% 2A′character and the vibrationally averaged OH–OH2 hydrogen bond distance is 1.952 Å. The magnetic hyperfine constants for the OH proton in the complex are significantly altered from monomer values.