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Assignment of the Unstudied Spectra of Formaldehyde (H2CO) using a Detailed Quantum Mechanical Spectroscopic Model

Students from Parmiters School and Ryan Brady

Molecular spectra assignment is extremely useful in multiple fields, namely exoplanetary science where these works can reveal the chemical composition, thermodynamic properties, orbital dynamics, and even the weather of planets that orbit stars outside our solar system (exoplanets). It is also of critical importance for industry, where Formaldehyde spectroscopy is used to measure the efficiency of combustion engines; in environmental science, since H2CO is a carcinogen and its abundance within the Earth’s atmosphere needs to be measured; and in the understanding of planetary formation since H2CO and its isotopologues are expected to be formed within proto-planetary disks.


This project involved the spectroscopic assignment of an unstudied region of Formaldehydes rovibronic absorption spectrum in the range 6730-6810 cm-1. The spectral line assignment included a labelling of quantum numbers to the upper and lower states of the associated transition as well as fitting the line profile with Voigt curves allowing the extraction of profile parameters such as the position, Full Width at Half Maximum (FWHM), and area. The class used a python script for the quantum number assigning interface as well as the program ‘FITYK’ to fit the line profiles using Voigt functions. This resulted in the assignment of over 50 lines, and the confirmation of 38 lines in total. The confirmation was done using a Combination Difference test, which involves finding clusters (>2) of transitions to the same upper quantum state, calculating their energies, and seeing whether they agree to within experimental uncertainty.

This new identification of spectral lines for Formaldehyde will be valuabel for exploration of exoplanets and industry uses alike. The group hope to write a scientific paper about the new result in the near future. Similar projects exploring the spectral lines of molecules have also produced other scientific papers which can be explored here: Orbyts Publications

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