Methylmercapto radical reactions: kinetics and product identification via frequency comb spectroscopy


Contact Dr Julia H. Lehman to discuss this project further informally.

Project description

Thionitrites, or s-nitrosothiols, have the form RSNO, where R is any organic group. Thionitrites are proposed atmospheric intermediates in the oxidation of reduced sulphur compounds in the presence of NO. For example, CH3SNO was experimentally observed as a reaction intermediate in high NOx environments following the OH oxidation of dimethylsulphide (DMS) (H. Niki et al, J. Phys. Chem. 1983, 87, 7). Reduced sulphur compounds, such as H2S, DMS, dimethyl disulphide (DMDS) and alkyl substituted mercaptans (RSH), are generated primarily from biogenic sources and supply a net flux of sulphur in the atmosphere. These reduced compounds are oxidized, becoming a source for atmospheric SO2 (contributing to tropospheric aerosol formation) and carbonyl sulphide (contributing to the stratospheric sulphate layer). This project will focus on the radical-radical reaction, CH3S + NO, in the synthesis of methyl thionitrite, CH3SNO. In this project, you will measure reaction rate constants at room temperature using laser photolysis combined with a cutting-edge laser-based detection method: cavity-enhanced mid-infrared frequency comb vibrational absorption spectroscopy.

As demonstrated by the Ye group at JILA, University of Colorado, Boulder, USA (B. J. Bjork et al, Science, 2016, 354, 444), cavity-enhanced frequency comb spectroscopy can be used to simultaneously obtain a broadband, high-resolution vibrational absorption spectrum, as well as reaction rate constants. This powerful technique, made possible by the pioneering work of Jan Hall and Ted Hänsch for which they were awarded the 2005 Nobel Prize in Physics, will be applied to the radical-radical reaction of CH3S + NO, forming CH3SNO. You will measure the vibrational absorption spectra of reactants, products, and any intermediates in this reaction. You will also use this technique as a detection method to monitor the reaction progress and derive room temperature reaction rate coefficients. You will interpret the laboratory measurements with the aid of theoretical methods, including quantum chemical calculations, spectroscopic modelling, and the opportunity to collaborate within the Atmospheric and Planetary Chemistry group to use your results in atmospheric modelling.

This PhD will provide a broad spectrum in training, particularly covering vibrational absorption spectroscopy, kinetic methods, high-resolution laser-based spectroscopic techniques, optics, vacuum systems, and quantum chemical calculations. You will also receive training in writing and implementing computer controlled data acquisition and analysis programs. You will be part of the well-funded, active, and highly collaborative Atmospheric and Planetary Chemistry group within the School of Chemistry.

Entry requirements

Applications are invited from candidates with or expecting a minimum of a UK upper second class honours degree (2:1), and/or a Master's degree in a relevant subject.

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is the ‘Methylmercapto radical reactions: kinetics and product identification via frequency comb spectroscopy’ as well as Dr Julia H. Lehman as your proposed supervisor.

If English is not your first language, you must provide evidence that you meet the University’s minimum English Language requirements.

If you require any further information please contact the Graduate School Office

We welcome scholarship applications from all suitably-qualified candidates, but UK black and minority ethnic (BME) researchers are currently under-represented in our Postgraduate Research community, and we would therefore particularly encourage applications from UK BME candidates.  All scholarships will be awarded on the basis of merit.