Knowledge Bank

Although several analyses of the $A2\Sigma +-X2\Pi i$ band systems of the OH and OD free radicals have been attempted, no consistent theory has been developed to explain the complex rotational structure. Here, we present a pseudo infinite-order perturbation approach which simply accounts for spin-orbit and spin-rotation interaction and accurately predicts the ultraviolet spectrum, the infrared spectrum, the pure rotational spectrum and the microwave lambda doubling spectrum. Molecular constants and parameters are derived and compared between the isotopes.