Hot line lists for open-shell molecules: Method development

Thousands of exoplanets have been discovered in the recent years. These planets are generally quite unlike those in our solar systems and astronomers have taken the first steps in
characterising these exoplanetary atmospheres through spectroscopy. In the last few years there has been significant progress made with observational facilities and atmospheric
modelling and inference methods for the observations. New instruments have opened up a greater wavelength range at high spectral resolution. As well as obtaining strong chemical signatures from hot Jupiters, such instruments are also capable of probing smaller and cooler planets around bright nearby stars. Hence we are on the cusp of atmospheric characterisation of exoplanets with temperatures 500-1500 K with high resolution observations at a resolving power of R=50,000.

However, a prerequisite for these advances to be made is the availability of the laboratory data necessary for interpreting these new observations. The unusual conditions found on most of the known exoplanets, involving elevated temperatures and high fluxes of stellar radiation, means the required data is not readily measurable in the laboratory. The project aims to address this issue and provide the data which will underpin the next great advance in our understanding of these new worlds. The project will provide the required data with a particular emphasis on obtaining precise wavelengths for key molecules for use in high resolution spectroscopic studies performed by telescopes such as the VLT. These data will be distributed as widely as possible through the ExoMol website and other databases.

The oxygen molecule is an obvious candidate to be a tracer of life in exoplanets. The pair of oxygen or ozone in combination with a reduced gas, methane, is a prominent biosignature, which should be detectable in the IR and NIR. The existing experimental line lists for oxygen are incomplete both in the temperature and wavelength coverage. Oxygen is a non-polar, open-shell molecule, whose electric dipole spectrum is forbidden both in IR and Vis. This project aims to compute high-resolution quadrupole and magnetic dipole line lists for O2, which will require developing a new computational approach for the quadrupole and magnetic dipole spectra of open-shell diatomic molecules. The line list should help the discovery of oxygen in atmospheres of exoplanets, an important step for detection of biosignatures in worlds beyond our solar system.