  Here we present a study of non-LTE effects on the exoplanetary spectra of a
collection of molecules which are key in the investigation of exoplanet
atmospheres: water, methane, carbon monoxide and titanium oxide. These
molecules are chosen as examples of different spectral ranges (IR and UV),
molecular types (diatomics and polyatomics) and spectral types (electronic and
ro-vibrational); the importance of different vibrational bands in forming
distinct non-LTE spectral features are investigated. Most notably, such key
spectral signatures for distinguishing between the LTE and non-LTE cases
include: for CH4 the 3.15 $\mu$m band region; for H2O the 2.0 $\mu$m and 2.7
$\mu$m band regions; for TiO, a strong variation in intensity in the bands
between 0.5 and 0.75 $\mu$m; and a sole CO signature between 5 and 6 $\mu$m.
The analysis is based on the ExoMol cross sections and takes advantage of the
extensive vibrational assignment of these molecular line lists in the ExoMol
database. We examine LTE and non-LTE cross sections under conditions consistent
with those on WASP-12b and WASP-76b using the empirically motivated
bi-temperature Treanor model. In addition, we make a simplistic forward model
simulation of transmission spectra for H2O in the atmosphere of WASP-12b using
the TauREx 3 atmospheric modelling code.

Earth and Planetary Astrophysics