Dynamics and Kinetics of Molecular Collisions
Collisions between molecules resulting in energy transfer or reaction are the fundamental interactions of chemistry. The research in my group is aimed at deepening our understanding of these elementary steps, and uses the unique properties of lasers to prepare and probe the reagents and products. This work is carried out jointly with Prof Ken McKendrick (see our joint research group webpages).
1. Stereodynamics of Gas-Phase Collisions
Measurement of vector properties (the stereodynamics) of gas-phase collisions are a sensitive probe of the forces involved. We use a variety of sensitive spectroscopic techniques to study collisional energy transfer, in particular crossed molecular beams with velocity-map ion-imaging and frequency modulated spectroscopy (figure 1). We interpret the results with the help of quantum scattering calculations, often performed by collaborators in other institutions..
Figure 1. Velocity-map ion-images of NO(A2S+, N') scattered from Ne in a crossed-beam apparatus, for different probe laser polarizations. The variation in intensity reflects changing rotational polarization as a function of scattering angle..
2. Roaming Atoms and Molecules
A new dynamical channel in molecular photodissociation has recently been identified, in which an atomic or molecular fragment ‘roams’ around its partner before reacting to form the products. The signature of a roaming channel appears in the coincident product state distribution. We have recently built a new velocity-map imaging spectrometer (figure 2), with the aim of identifying how common roaming reactions really are. This is in collaboration with Dr David Townsend (IPaQS) and Dr Stuart Greaves (ICS).
Figure 2. The newly constructed velocity-map imaging spectrometer, with the detector and flight tube pointing towards the camera..
3. Dynamics at the Gas-Liquid Interface
The dynamics of the elementary steps occurring at gas-liquid interfaces has seen very little study, despite their fundamental importance in atmospheric, combustion and other environments. This work, led by Prof Ken McKendrick, studies the inelastic and reactive collisions of OH radicals and oxygen atoms (figure 3) at surfaces that mimic atmospheric aerosols, or are of technological importance e.g. ionic liquids..
Figure 3. O(3P) atoms are formed by photolysis, fly to the liquid covered surface of a rotating wheel, and the returning OH radicals are probed by laser-induced fluorescence.