The Ultraviolet Emission Spectra of OH⁺ and OD⁺. Rotational Structure and Perturbations in the A³Πi–X³Σ⁻ Transition

The A 3 Πi–X 3 Σ − emission systems of OH + and OD + have been reinvestigated in detail. Fourteen bands have been analyzed (of which seven are new), and accurate rotational constants have been obtained for the levels ν = 0–2 in the two states of OH + and ν = 0–3 in the two states of OD + . Corrected assignments are given for the low J lines in the bands of OH + (which are important in astrophysical spectra, such as those of H 2 O containing comets).The perturbations in the A 3 Π states of both isotopes have been studied quantitatively, and the erratic Λ doubling explained in detail. The position of the perturbing b 1 Σ + state has been determined to within a few cm −1 , and minor perturbations by the A 1 Δ state have been characterized. Values of the spin–orbit coupling constant, A, and the spin–spin interaction parameter, α, have been extracted from the data for OD + A 3 Π ν = 0.