Dr Evans' Research Interests

Laser Induced Fluorescence Spectroscopy  

Computational Chemistry 
Infrared Spectroscopy 
Microwave Spectroscopy 
Selected Publications

 

Laser Induced Fluorescence

Many silicon-containing molecules have a potentially significant effect on the chemistry in space. Ten silicon-bearing molecules have been discovered in interstellar clouds or circumstellar shells, including the diatomics SiO and SiS, the carbon chain SiC4, and the two rings species, SiC2 and SiC3. Interstellar clouds are of interest to astronomers as they are often the sites of star and planet formation. Various carbon, hydrogen, nitrogen and silicon-containing species have been identified in well studied stars such as IRC+10216 (located 500 light years away in the constellation of Leo). The conditions in interstellar regions, such as very low densities of species and very low temperatures, give rise to relatively collision free environments. This means that various radicals are able to form and have extremely long lifetimes. With the abundance of silicon in space being quite large (it is the fifth most abundant element cosmically), in conjunction with the cosmic abundances of carbon, nitrogen, oxygen and hydrogen, there are potentially many new silicon molecules that might be formed and be observed. Our aim is generate new silicon species in our laboratory and to carry out spectroscopic measurements on them in order to ascertain their structures. The resulting data will then allow astronomers to detect these species in space.


In this work we use a high-voltage (10-15 kV) source (Telsa coil or car-ignition coil) to generate molecules of interest via a suitable precursor. The molecules of interest are then supersonically expanded into a vacuum chamber via a pulsed nozzle. The supersonic expansion results in the molecules being stabilised long enough so they can be probed using either laser induced fluorescence (LIF) or dispersed fluorescence (DF) techniques. Another result of the supersonic expansion is that it reduces the rotational and vibrational temperatures of the molecules, thus simplifying the resulting spectrum.
Currently we have carried out LIF and DF measurements on HSiNC and the previously unknown species HSiNCO.

A portion of the high-resoltion LIF spectrum of A1 - X1A transition of HSiNCO
A portion of the high-resolution LIF spectrum of A1A'' - X1A' transition of HSiNCO

The optimized structure of HSiNCO in its ground electronic state

 The optimized structure of the previous unknown HSiNCO molecule in its ground electronic state

 

Computational Chemistry

An understanding of the principles of quantum mechanics has yielded a number of theoretical methods for predicting the molecular properties of various systems. The Schrodinger wave equation, along with many of the fundamental concepts of quantum mechanics, was introduced in 1920s. This equation describes the properties of molecular structure in quantum mechanical terms, providing the foundation for many methods of electronic structure calculations.
Being able to accurately model molecular structure structures and reactions in chemistry can help describe many physically unobservable phenomena as well as resolve ambiguity in experimental results. With the capabilities of modern computers, accurate simulations of almost any molecule or reaction type are becoming a very real prospect, even for large biological molecules.
We have been using computational chemistry techniques to aid us in the identification of the spectral carrier in our LIF experiments as well as to predict the structure and stabilities of a number of new silicon and germanium containing species (e.g., HSiNCO and HGeNC)

We have also been using computational chemistry techniques to look at the possibility of forming stable helium containing compounds. Compounds containing covalently bonded Xe and Kr have been known since the early sixties; however, only in the last decade have a number of compounds containing Ar been observed (e.g., HArF and ArAuF). It is hoped that by using computational chemistry techniques a number of “stable” helium compounds can be identified and then hopefully detected spectroscopically.

HeAuF Image
HeAuF: a possible helium containing complex

              

Infrared Spectroscopy - Atmospheric Chemistry

In collaboration with Prof. Monks (Chemistry) and Prof. Remedios (EOS), we are developing an new infrared multipass cell to look at the reaction of monoterpenes and sesquiterpenes with tropospheric species in real-time. The aim of the work is to determine the reaction pathways and product yields. The work will be supported by computational chemistry studies. In addition to the infrared work, studies will also be carried out using microwave spectroscopy and proton-transfer mass spectrometry.

Microwave Spectroscopy - Atmospheric Chemistry

In collaboration with Prof. Don McNaughton and Dr Peter Godfrey we are studying the millimetre wave spectra of a number of terpene related compounds. Analysis of the jet-cooled millimetre wave spectra obtained at Monash University of three molecules linalool, verbenone and estragole have allowed us to determine, in conjunction with computational chemistry studies, the structure of these compounds. Scientific papers are currently been written on all three molecules and should be submitted in the next few months. This work will help atmospheric chemists understand the reactivity of these compounds much better and allow better modelling of their affects on the atmosphere (e.g., aerosol formation).

Estragole Conformer 1: Q-branch
Estragole Conformer 1: Q-branch

Selected Publications

  1. "The Millimetre Wave Spectrum of Estragole" Godfrey, P.D., McNaughton, D., Evans C.J. Chemical Physics Letters (Accepted for Publication) (2013) 
  2. "Development and chamber evaluation of the MCM v3.2 degradation scheme for β-caryophyllene" Jenkin M.E., Wyche K.P., Evans C.J., Carr T., Monks P.S., Alfarra M.R., Barley M.H., McFiggans G.B., Young J.C., Rickard A. R. Atmospheric Chemistry and Physics (2012), 12(11), 5275-5308
  3.  "Geometries and bond energies of the He-MX, Ne-MX, and Ar-MX (M = Cu, Ag, Au; X = F, Cl) complexes"   Evans, C. J., Wright, T. G.; Gardner, A. M. J. Phys. Chem. A (2010),  114(12), 4446-4454
  4. "Computational study on the energies and structures of the [H, Si, N, C, S] isomers" Evans C. J., Neil S. R. T. Theoretical Chemistry Accounts: Theory, Computation, and Modeling (2010), 127, 661-669 
  5. "Spectroscopic investigation of the A1A"-X1A' electronic transition of HSiNCO"   Dover, M. R.; Evans, C. J.; Western, C. M.  J. Chem. Phys. (2009), 131(12), Article No. 124302 
  6. "Spectroscopic Investigation of the Electronic A1A''-X1A' Transition of HSiNC"  Evans, C. J.; Dover, M. R., J. Phys. Chem. A. (2009), 113(30), 8533-8539  
  7.  “Computational study on the structures of the [H, Si, N, C, O] isomers: Possible species of interstellar interest” Dover, M. R.; Evans, C. J. J. Phys. Chem. A (2007), 111(50) , 13148-13156
  8. “Infrared spectroscopy of Li(NH3)n clusters for n=4-7”
    Salter, T. E.; Mikhailov, V. A.; Evans, C. J., Ellis, A. M. J. Chem. Phys. (2006), 125(3), Article No.: 034302
  9. “A three-dimensional multivariate image processing technique for the analysis of FTIR spectroscopic images of multiple tissue sections.” Wood, B. R; Bambery, K. R; Evans, C. J., McNaughton, D.; BMC Med. Imaging (2006), 6, 12. 

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Contact details

Dr C. J. Evans
Department of Chemistry
University of Leicester
LEICESTER
LE1 7RH

tel: 0116 252 3985

email: cje8@le.ac.uk