Osnabrück 2002 – scientific programme

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MO: Molekülphysik

MO 4: Femtosekundenspektroskopie II: Wellenpaketdynamik und reaktive Prozesse

MO 4.5: Talk

Monday, March 4, 2002, 17:30–17:45, HS 15/E07

Mapping of Electronic Changes in Na2 by Femtosecond Pump-Probe Photoelectron Spectroscopy — •Matthias Wollenhaupt, Andreas Assion, Oksana Bazhan, Dirk Liese, Cristian Sarpe-Tudoran, Marc Winter, and Thomas Baumert — Universitaet Kassel, 34132 Kassel

Insight in the dynamics of the control of chemical reactions can be accomplished if structural as well as electronic changes in the molecule can be monitored. In the Na2 molecule the coupling of a covalent and a ionic-type potential give rise to the double minimum potential showing electronic changes along the internuclear coordinate. In our experiment measurements of kinetic photoelectrons using time-of-flight spectrometry (TOF) combined with a femtosecond multiphoton ionization pump-probe technique in a molecular beam allow to map molecular motion with sub-Angström spatial and femtosecond temporal resolution. A pump laser pulse at 344 nm prepares a wave packet in the double minimum state at an energy slightly above the barrier between the inner and outer well. The time delayed probe laser at 267 nm ionizes the sodium molecule to bound and repulsive ionic states, which permit to map the complete range of energetically allowed internuclear distances. The change of the electronic structure is monitored by the internuclear distant dependent ionization yield. Fourier plots of the measured photoelectron spectra show distinct maxima corresponding to vibrational wave packet motion at the outer turning point of the double minimum potential.