Physics projects for Y3 and Y4 students

Project description

Diatomic molecules in sunspots: Theoretical & computational calculation of spectra

(supervisor: Maire Gorman)

Nature of project: theory, software

Available to students on full-time physics degree schemes or joint students.

Project description and methodology

This challenging project is suited to student(s) who have an aptitude for coding and are interested in theoretical molecular spectroscopy.

To date over 60 diatomic molecules have been detected in sunspots.

The primary aims of this project are to:

1. Identify experimental wavelength measurements in literature for a range of molecules which have been detected in sunspots.

2. Write code to compute the theoretical rotational intensities of these transitions by using knowledge of molecular spectroscopy. You will need to look at literature to select the relevant Honl-London factors depending on the type of transition. Thus this process, if successfully done, will result in a database of experimentally measured transitions with corresponding rotational intensities. Honl-London factors are simply equations to calculate the intensity of transitions which depend on the type of transition which a molecule is undertaking.

A successful project will develop beyond the above in one/some of the following directions:
1. Write code to streamline the experimental data extraction process.

2. Undertake a MARVEL analysis to check for self-consistency within the gathered data. MARVEL is an acronym for Measured Active Rotational-Vibrational Energy Levels: in a MARVEL analysis experimentally measured wavelengths are analysed for to check for i) self-consistency, ii) correct quantum number assignments and hence converted into "spectroscopic networks" of energy levels.

3. Using the generated list of experimentally measured transitions and computed intensities, spectra can be modeled for a range of temperatures and pressures.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: When an atom or molecule is exposed to a magnetic field the energy levels are shifted: this shift in energy levels causes wavelengths observed to change. By examining this change in spectra, there is a possibility that these molecules could be used as tracers of magnetic field strength within sunspots but also for brown dwarfs.

A challenge for a Y4 student would be to write code to compute the Landé-g factors for the energy levels involved in each transition and thus compute the Zeeman-shifted wavelengths for a range of magnetic fields and molecules. In the Zeeman effect a factor which is dependent on the magnetic field strength and Landé-g factor is added to the unperturbed energy level. Landé-g factors are computed using the quantum labels for each energy level.

Please speak to Maire Gorman (mng2) if you consider doing this project.

Initial literature for students:

  1. Hönl–London Factors for Doublet Transitions in Diatomic Molecules, Bennett, Mon. Notices Royal Astron. Soc 147 (1970), issue 1, P35-46,
  2. Diatomic Hönl-London factors computations, Hornkohl et al, Laser Applications to Chemical and Environmental Analysis (2004), paper TuE9.
  3. Predicted Landé g-factors for open shell diatomic molecules, Semenov et al, J Mol Spec 330 (2016), P57-62
  4. http://exomol.com/

Novelty, degree of difficulty and amount of assistance required

No prior knowledge of molecular spectroscopy is required but a keen interest is essential. The essential theory is partially covered in a Y3 core module.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Identification of experimentally measured wavelengths for diatomic molecules of interest in sunspotsend of October
Detailed understanding of Honl-London factor theoryChristmas
Code written to compute Honl-London factors for one type of transitionend of February
Code expanded for all types of transitions and used for moleculesEaster