The impact of L-uncoupling on Einstein coefficients for the OH Meinel (6,2) band: implications for Q-branch rotational temperatures

Abstract

A recent high-precision study of the J-dependent rovibrational branching in the aeronomically important OH Meinel (M) (6,2) band has demonstrated that the available theoretical and semiempirical Einstein coefficients fail to adequately describe the branching, especially in the case of Δ J=0 ( Q-branch) transitions. We suggest that the heterogeneous perturbation associated with rotational-electronic mixing of the X and A states ( L-uncoupling) is the primary source of this disparity. In support of this hypothesis, perturbation-theory calculations, based on an accurate, experimentally verified, ab initio A– X electric dipole moment function, have yielded rovibrational branching in good accord with experiment. Further, we show that OH M (6,2) Q-branch-based determinations of rotational temperatures and band emission rates contain significant systematic errors irrespective of the specific choice of theoretical/semiempirical A coefficients used in the analyses. Thus, these new results have special implications for the interpretation of M (6,2) Q-branch data, e.g. that obtained with the Spectral Airglow Temperature Imagers which were recently developed as part of the Planetary Scale Mesopause Observing System Project.