A Computational Approach to Modelling Molecular Biosignatures

Cross, Thomas M.

Abstract

This thesis presents a new computational method to model molecular biosignatures, using quantum chemistry techniques. To begin complimenting high resolution studies such as JWST, the fundamental vibrational band (ν = 0 → 1) has been selected to model.
Owing to the biosignature data availability issue, where in only key molecules such as water and methane have been extensively studied out of a potential 16,000+, a large scale approach is needed. Most current computational methods are either high accuracy but with the caveat of a large computational and temporal cost or utilise simpler methodology but have potentially low accuracy.
This project introduces an intermediate method which marries theory from both methods. This allows the production of an approximate methodology that is low in cost but of higher accuracy than simpler methods such as harmonic. This intermediate method utilises TOSH theory, and introduces the novel concept of using the anharmonic shift parameter σ to anharmonically correct the molecular geometry. This in turn allows the calculation for the vibrational excited rotational constants.
This work has produced three new codes, Prometheus, Epimetheus and Pandora. Prometheus calculates the spectroscopic parameters and uses an internal simple modelling process to produce spectra. Epimetheus extends further than Prometheus and can calculate the spectroscopic constants for triatomic molecules. Finally, Pandora produces spectra for asymmetric triatomic molecules.
It has been found this intermediate approach fairs well, typically producing data with a high-level approximation of the high-resolution databases such as HITRAN and ExoMol with some loss in accuracy for certain vibrational modes. Additionally this project has produced new data for isotopologues, which are currently not provided by other databases.

Citation

Cross, T. M. (2025). A Computational Approach to Modelling Molecular Biosignatures. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/5292460

• Thesis Type: Thesis
• Deposit Date: Jul 31, 2025
• Publicly Available Date: Aug 7, 2025
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/5292460
• Additional Information: Physics; University of Hull
• Award Date: Jun 3, 2025