Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses.

Rebecca Boll,Christoph Bostedt,John D Bozek,Catalin Miron,Sebastian Trippel,Sebastian Schorb,Minna Patanen,Daniel Rolles,Ryan Coffee,Cédric Bomme,Jochen Küpper,Mitchell Burkett,Thomas Kierspel,Artem Rudenko,Benjamin Erk,Simone Techert,Michelle Swiggers,Kiyoshi Ueda,Ken Ferguson ,T Osipov ,L Foucar ,M Simon ,S Carron ,T Marchenko

doi:10.1063/1.4944344

Abstract

Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse.

Highlights

Its microscopic understanding is crucial for emerging photosynthetic,3,4 photocatalytic,5 and photovoltaic6,7 applications
We present the results of a femtosecond pump-probe experiment conducted at the Linac Coherent Light Source (LCLS), aiming at studying electron transfer dynamics following inner-shell ionization of a halogen atom in gas-phase iodomethane (CH3I) and fluoromethane (CH3F) molecules
The spectrum created by the X-ray pulse contains a large proton peak, CHþx fragments, F2þ and F3þ ions, and a small amount of Fþ, F4þ, C2þ, C3þ, and C4þ. By comparing this spectrum with single-photon synchrotron data recorded at the same photon energy,33 it can be concluded that the F3þ and F4þ ions, as well as most of the F2þ, C2þ, C3þ, and C4þ ions, are produced by multi-photon X-ray absorption

Summary

Introduction

Its microscopic understanding is crucial for emerging photosynthetic, photocatalytic, and photovoltaic applications. The availability of short-pulsed extreme ultraviolet and X-ray sources, such as high-order harmonics of optical lasers or free-electron lasers (FELs), opened up the way to perform femtosecond time-resolved experiments involving inner-shell electrons, allowing to combine high spatial and temporal resolution. This has recently been exploited to study charge rearrangement processes following multiple core ionization of molecules at the Free-Electron Laser in Hamburg (FLASH), the Linac Coherent Light Source (LCLS), and the SACLA XFEL facility.. The subsequent 1.7 nm (727 eV) X-ray probe pulse mainly

Methods

Results

Conclusion