Dresden 2011 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 12: Femtosecond Spectroscopy III
MO 12.10: Vortrag
Mittwoch, 16. März 2011, 12:45–13:00, TOE 317
Ultrafast time-resolved photoelectron spectroscopy of benzene — •Peter Lang1,2, Christian Homann1, Igor Pugliesi1, Reinhard Kienberger2, and Eberhard Riedle1 — 1Dep. for biomolecular optics, LMU Munich — 2Dep. for physics, TU Munich
Time resolved photoelectron spectroscopy is a versatile tool for the investigation of ultrafast dynamics in optically dark regions of the molecular potential energy surface. We developed a novel pump-probe-setup, which consists of a magnetic bottle and two tunable laser pulses with pulse durations better than 30fs. The pump pulse covers a range of 240 - 400 nm and is used to excite the molecule. The temporally delayed probe pulse with 200 - 240 nm ionizes the excited molecules. This deep-UV probe pulse samples a large range of the electron kinetic energy spectrum up to 3 eV. The tunability allows to minimize the contribution of electronic excitations by the probe pulse alone.
Since the energy distribution in the excited molecule changes through electronic and vibrational and electronic relaxation, the kinetic energy of the electrons changes as a function of pump-probe delay. While the magnetic bottle is used to measure the electron kinetic energy, we can also record ion mass spectra to detect possible fragmentation products.
With a pump-probe cross correlation of better than 40 fs we are able to directly observe the ultrafast S2-S1 relaxation of benzene. The measurements show a shift in the electron spectra towards smaller kinetic energies as the molecule relaxes into the S1-state. This process occurs within less than 100 fs.