Sub-20 fs photoelectron spectroscopy (PES) utilises a femtosecond UV pump pulse (tunable between 190 and 400 nm) to excite the molecule and a second time-delayed probe pulse to ionise it. The energy distribution is analysed with a magnetic bottle spectrometer and the angular dependence of the photoelectrons by means of a velocity map imaging detector. In a later stage, the use of 20 eV probe pulses is envisioned to access higher-lying states in molecular ions and thereby obtain additional differentiation. The photoelectron spectrum reflects the temporal electronic and conformational evolution of the initially excited state. Here we will focus on photoinduced charge transfer (CT) processes. The CT induces a large change in the excitedstate geometry and energy resulting in well-separated bands in the photoelectron spectrum. We will compare the CT dynamics in the gas phase with that in polar solvents. To investigate the interplay of CT and solvation we plan to install a liquid micro-jet in the vacuum apparatus, as demonstrated recently for the study of the hydrated electron. For molecules undergoing photoinduced bond cleavage (see Fig. B.2.3) PES will allow us to determine the relative importance of homolysis and heterolysis.
High-level electronic-structure calculations will be used to characterise the electronic potential-energy surfaces of the molecular systems. The relevant reactive coordinates will be extracted from on-the-fly molecular dynamics calculations. Quantum wave-packet dynamics calculations will be performed to follow the ultrafast dynamics and provide the time-dependent wavefunction as input for the theoretical evaluation of the photoelectron signal. Efficient methods for the ab initio computation of boundcontinuum matrix elements required for the simulation of time and frequency-resolved photoelectron spectra will be developed in the theory group.
The setup for sub-20 fs photoelectron spectroscopy is developed in close cooperation with Prof. A. Stolow (Ottawa). His present key postdoc will join the MAP group before the end of the 1st fp and the investigated molecules will be determined. Close collaborations are maintained with Prof. A. L. Sobolewski (Warsaw).
He directly collaborates with the experimental groups on time-resolved measurements of molecules of biological interest, photostabilisers or molecular switches. He will also deepen the already established collaboration with the theoretical groups in MAP.