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Modelling phosphine spectra for the atmospheric characterization of cool stars and exoplanets

Sousa Silva, C; (2015) Modelling phosphine spectra for the atmospheric characterization of cool stars and exoplanets. Doctoral thesis , UCL (University College London). Green open access

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Abstract

Understanding the molecular composition of astrophysical atmospheres depends on the interpretation of their spectra, which is possible through a combination of observational data analysis and computational modelling. However, this process is difficult to perform as the observed spectra have an extremely rich structure and their opacity is dominated by multiple and complex molecules. These issues can only be addressed through a sophisticated understanding of molecular behaviour, together with fundamental data for all the species that contribute significantly to an atmosphere’s opacity. The present work describes the motivation and requirements for the creation of molecular line lists, and their applications. It specifically focuses on phosphine, PH3, due to its relevance in both earthly and astronomical studies, in particular cool stars and exoplanets. A complete line list for phosphine is presented, having been generated by employing ab initio quantum mechanical methods, performing an empirical refinement based on experimental spectroscopic data and harnessing high performance computing. A full account of how the spectral data were obtained, from the creation of the requisite surfaces to the production of cross-sections, can be found in these pages. An analysis of the partition function and associated thermodynamic properties of both phosphine and ammonia, NH3, is also done. Additionally, ongoing work from a preliminary investigation into the use of selected symmetries to produce fast and inexpensive low resolution spectra is described, and results from an introductory study of the tunnelling motion of phosphine are presented. The connections between past, present and future work are discussed, as well as their applications to the fields of astronomy and molecular physics.

Type: Thesis (Doctoral)
Title: Modelling phosphine spectra for the atmospheric characterization of cool stars and exoplanets
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1470247
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