Photoelectron spectroscopy on molecules
In a collaboration with the group of Prof. Riedle from the Institute for BioMolecular Optics at the Ludwigs-Maximilians-Universität within the Cluster of Excellence "Munich Centre for Advanced Photonics" time resolved photoelectron spectroscopy (TRPES) of molecules is performed.
The photochemistry of organic molecules, which is the triggering of chemical reactions due to the absorption of a photon by one of the educts, is of great interest for a variety of natural sciences from the photostability of DNA to new methods to synthesize drugs and the systematic study of fundamental building blocks of organic chemistry and biochemistry. Chemical reactions take place on two timescales. First absorption of a photon induces a reorganization of the electron densitiy, which happens on the attosecond to few femtosecond timescale, and lead to the actual chemical reaction, which is a reorganization of atom positions and change in the bonding between the atoms and which happens on a timescale between ten femtoseconds and hundreds of picoseconds [1].
We generate short and tunable pulses in the ultraviolet using frequency doubled light from two noncolinear optical parametric amplifiers (NOPA) [2] pumped by a titanium sapphire regenerative amplifier, which are overlapped with a molecular beam from a heated valve inside a high vacuum chamber. The first pulse excites the molecule resonantly into one of its lowest lying electronic excited states and induces a chemical reaction. The second pulse ionizes the excited molecule. The kinetic energy is measured with a so called magnetic bottle spectrometer [3].
The investigation of photochemical reactions of organic molecules in the gas phase complements experiments done in Prof. Riedle’s group on broadband transient absorption in liquid phase and we expect to generate important insights on the interaction of molecules and solvents during chemical reactions.
[1] "Ahmed Zewail - Nobel Lecture: Femtochemistry: Atomic-Scale Dynamics of the Chemical Bond Using Ultrafast Lasers"
[2] T. Wilhelm, J. Piel, E. Riedle, "Sub-20-fs pulses tunable across the visible from a blue pumped single pass noncollinear parametric converter", Opt. Lett. 22, 1494 - 1496 (1997)
[3] A.M Rijs, E.H.G Backus, C.A De Lange, N.P.C Westwood and N.H.M Janssen, “‘Magnetic bottle’spectrometer as a versatile tool for laser photoelectron spectroscopy”, Journal of Electron Spectroscopy and Related Phenomena 112, 151 - 162 (2000)