Dissociative ionization of molecules by intense laser fields and its application for probing ultrafast chemical dynamics

(S.A. Trushin, Sfb-Kolloquium am 04.11.03, HS A, FB Physik)

At laser intensities close to the threshold for barrier suppression ionization all molecules are efficiently ionized. Ionization is often followed by extensive fragmentation. Detailed investigation of ionization of metal carbonyls by 30-100 fs pulses at 0.8-1.3 µm in the intensity range of 1-100 TW cm^-2 reveals that resonances in ions enhance their fragmentation. Using ionization by the electric field of intense laser radiation offers some advantages to study the dynamics of ultrafast chemical reactions in pump-probe experiments: Any electronically excited state is expected to give an enhanced ion signal independent of its electronic and vibrational nature, depending mainly on its ionization potential; ionization is followed by extensive fragmentation which provides additional information on transient intermediate states and/or species. Monitoring the pump-probe delay kinetics of the parent and various fragment ions, we are able to follow the molecule from state to state all along the primary photochemical reaction path which is often completed within few hundreds of femtoseconds.