My scientific research concerns the experimental study of photon-molecule interactions using angle resolved photoelectron spectroscopy, dispersed fluorescence polarisation spectroscopy and various photoelectron-photoion coincidence techniques.The majority of this work has been carried out with synchrotron radiation on NINA (UK), Bonn (Germany), SURF (USA) or the SRS (UK).
The central theme underpinning these investigations is to examine the way resonant phenomena, such as autoionisation, Cooper minima, shape resonances or vibronic coupling, influence molecular photoionisation dynamics. The angle resolved photoelectron studies have concentrated on medium sized polyatomic molecules, particularly ring-type molecules, such as the halobenzenes, halothiophenes and halouracils.
The aim is to investigate the way in which the orbital character (mainly σ, π or halogen np) affects the photoionisation dynamics. The breakdown of the single particle model for inner valence molecular orbital ionisation, due to electron correlation, has been studied.
Resonances also play a significant role in molecular dissociation dynamics. In particular, the competition between autoionisation and predissociation into neutral products in the decay of super-excited states has been investigated by measuring photoionisation quantum efficiencies. Coincidence methods have been employed to investigate unimolecular decomposition in polyatomic molecular ions and the effect of ion residence time on the fragmentation dynamics has been explored.
A velocity map imaging spectrometer has been developed, suitable for gas phase studies using either synchrotron radiation or laser excitation, and has been used to study the effect of electronic or vibrational autoionisation on vibrational or rotational populations, respectively, in diatomic molecules. Time-resolved, pump-probe, photoelectron studies have also been performed.
Following the closure of the SRS, my experiments using synchrotron radiation are continuing at the Canadian Light Source and at Soleil. I have also participated in work at FLASH and at LCLS.
David Holland's Publications (link opens in a new window).