Mitev, Georgi B;
(2024)
Spectroscopy and photodissociative processes of diatomic molecules.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
In the wake of novel high-resolution spectroscopic techniques, the launch of the James Webb Space Telescope, and in preparation for the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) mission, the modelling of exoplanetary atmospheres has increasingly required complete molecular datasets in the form of line lists which meet the high resolution standard. By applying rigorous quantum mechanical treatments informed by experimental data, line lists are generated for the terrestrially significant radical species sodium monoxide (NaO) and hydoxyl (OH), which has been detected in a wide range of exoplanetary, stellar, and interstellar environments. Ab initio electronic structure calculations, spectroscopic model refinement, and a number of post-processing techniques are combined to produce these data. Measured Active Rotational-Vibrational Energy Level (MARVEL) energy levels substitute equivalent levels in the OH line list, with rigorously estimated uncertainties in experimentally dark regions, following the hybridization procedure. Strong focus is placed on the dissociative processes of OH. Most current photodissociation databases do not consider temperature, which is not suitable for high-resolution studies of hot-exoplanets, motivating techniques to produce temperature dependent photodissociation cross sections and rates. The photodestruction of molecules through photodissociation is of high astrochemical importance in the presence of radiation rich environments, particularly in the evolution of hot exoplanetary atmospheres which experience strong fluxes. Established post-processing methodology is generalised and automated for the efficient production of photodissociation cross sections. Predissociative effects such as spin-orbit predissociation broadens select transition lines in some species, allowing for detection of such molecules in optically thick regions and leads to a lower threshold for photodissociation. An implementation of the so-called stabilization method for the rigorous computation of predissociation widths of diatomic molecules is presented, with application to OH and SH, reproducing experimental resonances to high fidelity. In light of this, methods are also proposed for a more complete treatment of continuum states in general which are known to have a significant impact on the line positions of bound-bound absorption spectra.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Spectroscopy and photodissociative processes of diatomic molecules |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10201506 |
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