Spectral Characterization of Molecules in The Martian Atmosphere

Abstract

To gain insights into the behavior of water in the Martian atmosphere, a comprehensive examination of the OH radical (∙OH) is advantageous due to its involvement in water-related chemical reactions. Spectral data captured by space missions like the Emirates Mars Mission (EMM) and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission provide an opportunity to explore the characteristics of ∙OH, including its abundance across different longitudes, latitudes, and altitudes. This study focuses on constructing line lists of ∙OH molecule to analyze better emission spectra obtained from EMM or MAVEN. In addition, these line lists can be used to generate synthetic spectra of ∙OH at different temperature and pressure conditions. The process of generating these spectra involves four major steps: (1) calculation of potential energy curves (PECs), (2) determination of transition properties such as transition dipole moment (TDM) functions, (3) computation of line lists, and (4) construction of the synthetic spectra.

Line lists and spectra for the excited states of ∙OH were generated using computer programs Molpro, Pgopher, and EXOCROSS. Molpro is a suite of computational quantum chemistry computer codes that can be used to calculate PECs and transition properties, Pgopher is a program that simulates and fits rotational, vibrational, and electronic spectra, and EXOCROSS is a program that generates spectra and thermodynamic properties from line lists. Automating the process is desirable due to the time-consuming nature of these calculations. To address this, a computer program SpectroTool was developed. This automation reduces the execution time of a line list calculation from hours to minutes or even seconds. SpectroTool facilitated the computation of line lists representing transitions from the first and second excited electronic states of ∙OH to its ground state. The wavelengths of the investigated spectral lines for the transitions between the first excited state and the ground state range between 230 nm and 575 nm, while those for the transition between the second excited state and ground state range between 144 nm and 294 nm. These transitions include lines within the observable range of MAVEN’s Imaging UltraViolet Spectrograph (IUVS), i.e., between 110 nm and 340 nm.

To compare the calculated spectra with MAVEN-acquired spectra, a complementary code GlowingMars was developed. The aim of GlowingMars is to enable the comparison of synthetic and observed spectra obtained from space missions dedicated to studying the Martian atmosphere, but currently it only supports MAVEN. GlowingMars aims to identify an observed spectrum that best matches a given synthetic one and provides relevant details such as longitude and latitude information. In this thesis, the capabilities of the newly developed GlowingMars program are demonstrated.

Date of Award	Apr 2023
Original language	American English
Supervisor	Nayla El Kork (Supervisor)