Infra-Red Spectroscopy

Infra-red (IR) spectroscopy is a powerful technique for probing the structure and bonding in molecules. Calculations of IR spectroscopy play a key role in understanding and assigning the bands observed in experimental spectra. We are interested in developing calculations of IR spectroscopy in four main areas:

  • Anharmonic frequency calculations: The aim of this research is to assess and improve the efficiency of IR frequency calculations beyond the harmonic approximation.

  • IR spectroscopy in excited electronic states: We are exploring the simulation of the IR spectroscopy of molecules in electronically excited states using time-dependent density functional theory and MOM approaches. This work is in collaboration with Prof Mike George who measures the spectroscopy via FTIR measurements. An example is the study of coumarins

    Coumarin Spectra

  • Simulation of IR spectroscopy using empirical potentials: The calculation of IR spectroscopy of large systems with quantum chemical methods becomes computationally intractable. One solution to the calculation of the IR spectroscopy of large systems is the use of empirical potentials. Here the challenge is to develop force fields with sufficient accuracy. Examples are the IR spectroscopy of nanotubes.

  • 2D-IR spectroscopy of the amide I mode: For larger molecules, IR spectra often become congested with many overlapping bands that can make the spectra hard to interpret, with the consequence that much of the information contained within the spectra is lost. Through spreading the transitions over a second frequency domain, 2DIR reveals more information by exposing cross peaks that correlate with the coupling between different vibrational modes. We are exploring new approaches for the calculation of the coupling between amide I vibrational modes.

    Relevant Papers:

    Investigating the calculation of anharmonic vibrational frequencies using force fields derived from density functional theory.
    M.W.D. Hanson-Heine, M.W. George and N.A. Besley
    J. Phys. Chem. A, 116, 4417 (2012).

    Rapid anharmonic vibrational corrections derived from partial Hessian analysis.
    M.W.D. Hanson-Heine, M.W. George and N.A. Besley
    J. Chem. Phys., 136, 224102 (2012).

    Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins.
    M. W. D. Hanson-Heine, A. Wriglesworth, M. Uroos, J. A. Calladine, T. S. Murphy, M. Hamilton, I. P. Clark, M. Towrie, J. Dowden, N. A. Besley and M. W. George
    J. Chem. Phys., 142 , 154119 (2015).

    Calculation of the vibrational frequencies of carbon clusters and fullerenes with empirical potentials.
    H. Do and N.A. Besley
    Phys. Chem. Chem. Phys., 17, 3898 (2015).

    Interaction of the NO 3p(C2Π) Rydberg state with RG (RG = Ne, Kr and Xe): potential energy surfaces and spectroscopy.
    O. V. Ershova, J. Klos, N. A. Besley and T. G. Wright
    J. Chem. Phys., 142, 034311 (2015).

    Interaction of the NO 3pπ Rydberg state with Ar: Potential energy surfaces and spectroscopy.
    O.V. Ershova, J. Klos, J.P. Harris, A.M. Gardner, V. Tame-Reyes, A. Andrejeva, M.H. Alexander, N.A. Besley and T.G. Wright
    J. Chem. Phys., 138, 214313 (2013).