Berlin 2001 – wissenschaftliches Programm
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MO: Molekülphysik
MO 8: Posters Thursday: Dissociation and other Collision Processes
MO 8.5: Poster
Donnerstag, 5. April 2001, 12:30–15:00, AT3
CHARACTERIZATION OF ULTRAFAST FRAGMENTATION PROCESS AND FEEDBACK CONTROL IN ORGANOMETALLIC MOLECULES — •Cosmin Lupulescu, Marcel Krenz, Cristina Kaposta, Filip Budzyn, Porfirio Rosendo-Francisco, Stefan Vajda, and Ludger Wöste — Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin
In our contribution, we characterize the ultrafast fragmentation process in electronically excited Fe(CO)2(NO)2 and CpMn(CO)3 by means of femtosecond time-resolved spectroscopy combined with mass spectrometry [1]. In the two-color multi-photon ionization data experiment it was possible to record the transients of the parent molecule-ions and their photofragment ions. The observed transient ionic fragmentation patterns indicated an ultrafast loss of the CO ligands and the involvement of different intermediate states (different locations on the potential energy surfaces) in the process of photodissociation. In the next step, we performed a feedback control experiment on the photofragmenting CpMn(CO)3 molecular system in order to maximize the yield of desired ionic products CpMn(CO)+ and CpMn(CO)3+ through pulse modulation [2]. In the optimization experiment, a single laser beam (with wavelength centered at 800 nm) passes through a pulse shaper setup, which allows a simultaneous phase- and amplitude modulation of the laser pulses by applying voltages to a liquid crystal spatial light modulator (SLM) consisting of 2x128 pixels. By computer control, pulses of arbitrary form, like linearly chirped pulses, pulse trains etc. can be produced [3]. These shaped pulses are then focussed on the molecular beam and the current of the desired mass-selected product photoion is taken as feedback signal for the optimization algorithm [4]. The optimization algorithm alters the pulse shaper settings in order to maximize the desired ion signal. We apply an algorithm based on evolutionary strategies [5]. In order to avoid pulse intensity effects, only the phase was optimized. In the CpMn(CO)3 system, the pulse shapes obtained from optimization reflect well the intrinsic molecular dynamics during photofragmentation and the change of the CpMn(CO)+/ CpMn(CO)3+ intensity ratio shows a clear evidence for the capability of the feedback optimization method to find tailor-made system-specific pulses.
[1] A. Zewail et al., Chem. Phys. Lett. 233 (1995) 500-508
[2] M. Bergt et al. J. Phys. Chem. A 103, 10381 (1999)
[3] A. Weiner et al., IEEE J. Quantum Electron. 28 (1992), 1500
[4] S. Vajda et al., J. Chem. Phys. to be published
[5] H.-P. Schwefel, Evolution and Optimum Seeking, Wiley New York (1995)