ExoMol photodissociation cross-sections – II. Continuum absorption and pre-dissociation spectra for the hydroxyl radical

ABSTRACT The photodissociation of hydroxyl has seen much theoretical study and temperature-independent photodissociation cross-sections are available in the Leiden photodissociation and photoionization data base. Such cross-sections are important for calculations in UV rich environments, concerning not only abundances of hydroxyl but other hydrogen and oxygen containing species, notably water. Temperature-dependent photodissociation cross-sections comprised of smoothed transitions to continuum levels of the A $^2\Sigma ^+$, B $^2\Sigma ^+$, 1 $^2\Delta$, and 1 $^2\Sigma ^-$ electronic states and appropriately broadened pre-dissociative states of A $^2\Sigma ^+$, B $^2\Sigma ^+$, and C $^2\Sigma ^+$ are calculated. These are produced using the same model as the ExoMol OH line list, mythos and cover the temperature range of $T \in [100,200,...,8000]~\textrm {K}$ each with a grid spacing of 0.1 nm from 82.8 to 2000 nm. Compared to the data presented by Leiden we find increased photodissociation at long wavelengths due to pre-dissociation and strong temperature dependence of the photodissociation rates. The OH MYTHOS photodissociation cross-sections and results as a function of temperature are available for download via www.exomol.com and are also available in a form suitable for study of non-local thermodynamic equilibrium effects.