Düsseldorf 2007 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 23: Poster II - Interaction with strong or short laser pulses
A 23.7: Poster
Donnerstag, 22. März 2007, 16:30–18:30, Poster B
Time-resolved studies of CH4 fragmentation in intense laser fields — •Ulrich Wiedemann1, Artem Rudenko1, Thorsten Ergler1, Karl Zrost1, Bernold Feuerstein1,2, Claus Dieter Schröter1, Robert Moshammer1, and Joachim Ullrich1 — 1Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg — 2Physikalisches Institut, Universität Heidelberg, 69120 Heidelberg
The break-up of methane molecules exposed to intense laser fields has been studied using a combination of a 'Reaction Microscope' spectrometer and a femtosecond pump-probe setup. The time evolution of a particular fragmentation reaction (e.g., one- or few-electron dissociative ionization) induced by the 'pump' pulse (9 fs, 4x10^14 W/cm^2, central wavelength 780 nm) was probed with the identical 'probe' pulse arriving after a variable time delay. Using 3D Coulomb explosion imaging we were able to visualize the dissociation dynamics of the singly ionized methane molecule, and found that it strongly depends on the final localization of the charge, which is reflected in very different fragment angular distributions for the two reaction pathways (CH4+ => CH3 + H+ and CH4+ => CH3+ + H). Exploiting this dependence for the channel separation, we map the ionization probability for both pathways as a function of the delay, and, thus, of the internuclear distance. Moreover, similar to earlier results on the CH4 fragmentation by ion impact or VUV radiation, we observe that double ionization often leads to the formation of a hydrogen molecular ion. Possible mechanisms of this bond-forming reaction as well as the relevant time scales estimated from the experimental data will be discussed.