ExoMol line lists – LXI. A trihybrid line list for rovibronic transitions of the hydroxyl radical (OH)

ABSTRACT The hydroxyl radical (OH) is a species of high importance in exoplanetary studies, the interstellar medium, and in stellar spectra. Terrestrially, it is a significant component of combustion chemistry, an oxidizer in the upper atmosphere, and a source of telluric bands. Internally contracted multireference configuration interaction potential energy curves, spin-orbit couplings, electronic angular momentum couplings, and (transition) dipole moments for eight electronic states of OH are computed and refined against empirical energy levels to produce an OH spectroscopic model. A line list consisting of rovibronic term values, allowed electronic dipole transitions, Einstein-A coefficients, and partition functions for varying temperature and a continuum absorption data set are then produced by variational solution of the coupled-channel Schrödinger equations using the nuclear motion code Duo. Marvel energy levels substitute equivalent levels in the OH line list, with estimated uncertainties in experimentally dark regions, following an established hybridization procedure. Predissociation lifetimes of the A $^2\Sigma ^+$ state are calculated using a stabilization method and convoluted with natural lifetimes to include predissociative effects. Continuum absorption cross-sections for $T \in [100,200,...,8000]~\textrm {K}$ and zero pressure are provided in the range of $0\rightarrow 80\, 000$ cm$^{-1}$ with a step size of 0.01 cm$^{-1}$. Comparison with available literature cross-sections exhibits strong agreement. The line list is suitable for high-resolution studies up to 8000 K. The OH MYTHOS data set is available for download via www.exomol.com.