Abstract

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Electron transfer between the fragments of a dissociating molecule

I-24

Electron transfer between the fragments of a dissociating molecule


A. Rudenko1

1J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas, USA

Charge transfer and charge migration reaction drive numerous important processes in physics, chemistry and biology. Ultrashort X-ray pulses represent a very efficient tool for studies of charge transfer dynamics, combining element- and, thus, site-selectivity with femtosecond time resolution. Here, we used 70 fs X-ray free-electron laser pulses at 1.5 keV to image intramolecular electron transfer in iodomethane molecules during dissociation induced by a synchronized infrared (IR) laser pulse. Inner-shell X-ray ionization creates positive charge, which is initially localized on the iodine atom. We map the electron transfer between the methyl and iodine fragments as a function of their interatomic separation set by the IR-X-ray delay. As illustrated in Figure 1, the delay-dependent kinetic energy spectra of highly-charged iodine ions contain a band of extremely low-energy fragments, which can appear only if the remaining part of the molecule remains neutral and there is no Coulomb explosion. Therefore, the delay-dependent yield of this channel reflects the inversed probability of the electron transfer from the methyl group to the iodine atom. We observe signatures of this electron transfer up to 20 Å internuclear separation, show that its effective spatial range can be estimated from a classical over-the-barrier model [1], and discuss possible reasons for the observed oscillatory behaviour of the electron transfer rate.

Figure 1. Delay-dependent kinetic energy spectrum of the measured I6+ ions (top) and the yield of the lowest-energy channel (bottom)

Figure 1. Delay-dependent kinetic energy spectrum of the measured I6+ ions (top) and the yield of the lowest-energy channel (bottom)

References:

[1] B. Erk, R. Boll, S. Trippel et al., Science 345 288 (2014)).