Time-resolved photoelectron imaging is presented as a new method for the study of anion dynamics. Time-dependent photoelectron energy spectra and angular distributions are extracted from images taken during the dissociation of I 2 Ϫ at 793 nm, and used to follow in detail the dissociation dynamics from 0-1 ps.

Articles you may be interested inCommunication: Probing the entrance channels of the X + CH4 → HX + CH3 (X = F, Cl, Br, I) reactions via photodetachment of X−-CH4An ab initio molecular dynamics study of the S N 2 reaction Cl − +CH 3 Br→CH 3 Cl+Br − Time-resolved photoelectron spectroscopy of negative ions has been applied to study the title reaction as a model system for gas phase S N 2 reactions. Starting from the precursor cluster I 2 Ϫ •CH 3 I, the interaction of the reactants I Ϫ and CH 3 I is initiated by a pump pulse and the subsequent dynamics are observed with a delayed probe pulse used to detach the excess electron and measure their photoelectron spectra. Using two different pump photon energies, which lead to different amounts of internal energy available to the reaction complex, a number of dynamical features have been observed. For small internal excitation, the reactants only form stable, albeit vibrationally excited, I Ϫ •CH 3 I complexes. However, with increased internal excitation, complexes are formed that exhibit biexponential decay back to I Ϫ and CH 3 I reactants with time scales of 0.8 and 10 ps. Similar dynamics are expected for entrance channel complex formed in the first step of a gas phase S N 2 reaction.

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