Astrophysical Investigations of Carbon Monoxide in the Martian Atmosphere

Abstract

Carbon Monoxide (CO) is one of the most abundant diatomic molecules in the Martian atmosphere. It can formed through several processes, but mainly through the CO2 photodissociation 12. There are two main ways to excite the CO molecule. The first is collisional excitation, where the molecule gets excited to high rovibrational levels when colliding with electrons or atoms, such as atomic hot Oxygen (or other molecules). The second is photoexcitation, where photons are absorbed at a frequency suitable to the molecule’s transfer into a higher energy state. The first process plays a vital role in understanding the Oxygen escape mechanism from the Martian atmosphere. In contrast, the second is responsible for spectral signatures that could lead us to know more about the abundance of atoms and molecules in the Martian atmosphere. In this work, the collisional cross-sections of O+CO have been calculated using the coupled states approximation (CS) method, contributing to the Oxygen escape probability calculations. At the same time, new accurate molecular potential energy curves for the ground and the excited electronic states of the CO molecule are computed at the CASSCF/MRCI+Q level of theory as part of the photoexcitation process. To the best of our knowledge, this is the first systematic theoretical study of highly excited states of the CO molecule. A spectroscopic model for 𝐴1𝛱 − 𝑋1𝛴+,𝐵1𝛴+ −𝑋1𝛴+,𝐶1𝛴+ −𝑋1𝛴+,𝐷′1𝛴+ −𝑋1𝛴++, and 𝐸1𝛱 −𝑋1𝛴+transitions is presented. The 𝐵1Σ+ and 𝐶1Σ+ states, characterized by avoided crossings, have been diabatized to obtain accurate diabatic potential energy and transition dipole moment curves. The results have been validated by comparing the synthetic spectra with various experiments. The excellent agreement between our calculated spectra and the experimental data confirms the accuracy of our calculations. The electronic and rovibronic levels of CO are crucial in forward modeling for understanding the properties of the Martian atmosphere. The 𝐶1𝛴+ − 𝑋1𝛴+ and 𝐸1𝛱 −𝑋1𝛴+ transitions have been used by the Emirates Mars Mission science team for more accurate determination of Argon abundance through a density retrieval algorithm3.

Date of Award	17 May 2024
Original language	American English
Supervisor	Al Hajri (Supervisor)