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Title: Theoretical rotational-vibrational spectroscopy of XY3-type molecules of industrial relevance
Author: Coles, Phillip A.
ISNI:       0000 0004 8500 5686
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available