We use time-resolved photoelectron imaging to study ultrafast relaxation dynamics in isolated molecular anions. Using femtosecond lasers (where 1 fs is 1x10-15 s), we are able to track the excited state evolution on the timescale of nuclear motion. Anions are of course ubiquitous in the condensed phase. In the gas-phase however, many anions do not exist. For example, many polyanions simply have a too high electron density to be stable. Moreover, most singly-charged anions do not possess bound excited states. Despite this apparent contradiction with our goals of measuring excited state dynamics, we are able to generate a large number of isolated anions that are stable and do posses excited states. Current projects include: the study of polyanions; the dynamics of the radical anion product in a electron-transfer reaction; electron transfer reactions in real-time; biological chromophores; and the mapping of excited state dynamics through photoelectron angular distributions.
The picture is an illustration of what we actually measure - electrons striking a position sensitive detector. This provides information not only about the energy of the electron, but also the angle at which it was ejected with respect to the laser polarisation field. Click on the title for a more detailed overview of the experiment and specific projects.
Femtosecond laser pulses are used to generate solvated electrons at the water/air interface. Based on the knowledge that iodide ions reside at the surface, we excited the lowest charge-transfer-to-solvent band in iodide to inject the electron into the water at the water/air interface. The subsequent solvation dynamics are monitored using a second femtosecond laser pulse. As this interacts with the surface, a very small amount of radiation at half the wavelength of the driving light is generated (called the second harmonic or SH). This can only occur at the interface and thus, by monitoring this light, the interfacial dynamics can be monitored. The concepts are depicted in the figure and the amount of SH collected reflects the dynamics of the solvating electron and also its long-time dynamics. Click on the title for more information.
This project is in collaboration with Prof. Colin Bain