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Q: Quantenoptik

Q 434: Poster: Femtosekundenspektroskopie und ultrakurze Pulse (gemeinsam mit FV MO)

Q 434.8: Poster

Thursday, March 7, 2002, 17:30–19:30, Schloss

Time-resolved photoelectron spectroscopy of the I⁻ + CH₃I symmetric S_N2-reaction — •R. Wester, A. E. Bragg, A. V. Davis, and D. M. Neumark — Department of Chemistry, University of California Berkeley, Berkeley CA 94720, USA

The bimolecular symmetric nucleophilic substitution (S_N2) reaction of iodine anions with methyl iodide has been studied in real time using femtosecond photoelectron spectroscopy. At time zero a femtosecond pump pulse dissociates the I₂⁻ bond in the precursor complex I₂⁻(CH₃I), thereby initiating the (S_N2) reaction. The reaction dynamics are probed by photodetaching with a second femtosecond pulse and recording the photoelectron kinetic energy spectra for various delay times.

Several dynamical features are observed in the experiment: Within 100 fs of the pump pulse, I⁻ ions are found in the vicinity of CH₃I. Part of the I⁻ flux rebounds and pulls away within 1 ps; the remaining flux forms a vibrationally excited I⁻CH₃I complex that decays within tens of picoseconds back to I⁻ + CH₃I. These results will be compared to recent theoretical work for the Cl⁻ + CH₃Cl reaction.