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Theoretical rotational–vibrational spectroscopy of XY3–type molecules of industrial relevance

Coles, Phillip A.; (2019) Theoretical rotational–vibrational spectroscopy of XY3–type molecules of industrial relevance. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis presents research carried out as part of the ExoMol project in partnership with Servomex Ltd. The overarching aim has been to compute high-accuracy line lists for molecules of astronomical and industrial relevance, namely 14NH3 and 75AsH3. These line lists are to be used in high accuracy spectroscopic studies, atmospheric spectral retrievals, and to inform decisions regarding the development of new in situ gas analysers. // A high accuracy spectroscopic potential energy surface (PES) for 14NH3 has been produced by refinement of a recently published ab initio surface to carefully chosen experimental data. The resulting energy level predictions represent a 5–10 times improvement over the previous best predictions computed as part of the ExoMol project. Several new ab initio dipole moment surfaces (DMSs) were analysed, but were found to be generally inferior to an older surface available. Using the new PES and older DMS, a room temperature 14NH3 line list was produced for wavenumbers between 0 and 20 000 cm-1. // Exploratory NH3 measurements were performed at 1392 nm using second harmonic wavelength modulation spectroscopy. The measurements aimed to identify the key NH3 absorption features that might interfere with trace moisture detection in high purity NH3 used in the development of GaN based diode lasers. Line positions were derived for the strongest NH3 lines in this region, with an estimated uncertainty of 0.05 cm-1. // A room temperature 75AsH3 line list is produced for wavenumbers between 0 and 7000 cm-1, and suitable for use up to 300 K. The required PES and DMS were produced by fitting analytic expressions to a grid of nuclear geometries and dipole moments generated from electronic structure calculations. The PES is then refined to experimental data data to improve accuracy. Final line positions and intensities are suitably accurate for industrial modelling purposes.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Theoretical rotational–vibrational spectroscopy of XY3–type molecules of industrial relevance
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/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 > 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/10082248
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