Rotational, fine, and hyperfine structure in the high-resolution electronic spectrum of ArOH and ArOD

A number of vibrational bands of the à ²Σ ⁺↔X̃ ²Π electronic spectrum of both ArOH and ArOD have been investigated by laser induced fluorescence with a high-resolution, pulsed laser system yielding linewidths ≲ 250 MHz in the UV. This spectrum not only displays completely resolved rotational structure, but also fine and hyperfine structure. The hyperfine constants and precise interatomic distances derived from the rotational constants provide a very interesting picture of the electronic and geometric structure of the complex. The bonding is incipiently chemical in the à state with clear evidence for at least some electronic reorganization between Ar and the open-shell OH radical in the complex. Conversely, the X̃ state appears to be bound almost solely by physical van der Waals interactions characteristic of systems containing only closed-shell species.