Capturing molecular structural dynamics by 100 ps time-resolved X-ray absorption spectroscopy

Tokushi Sato,Ayana Tomita,Shin-Ya Koshihara,Kohei Ichiyanagi,Shin-Ichi Adachi,Hirohiko Ichikawa,Matthieu Chollet,Shunsuke Nozawa,Hiroshi Fujii

doi:10.1107/s0909049508034596

Abstract

An experimental set-up for time-resolved X-ray absorption spectroscopy with 100 ps time resolution at beamline NW14A at the Photon Factory Advanced Ring is presented. The X-ray positional active feedback to crystals in a monochromator combined with a figure-of-merit scan of the laser beam position has been utilized as an essential tool to stabilize the spatial overlap of the X-ray and laser beams at the sample position. As a typical example, a time-resolved XAFS measurement of a photo-induced spin crossover reaction of the tris(1,10-phenanthrorine)iron(II) complex in water is presented.

Highlights

time-resolved X-ray absorption spectroscopy (TR-XAS) can reveal the dynamics of the oxidation and valence states via XANES and the local molecular structure via EXAFS with sub-angstrom spatial resolution, which compliments diffraction and scattering techniques (Ihee et al, 2005; Kong et al, 2008)
Several groups have been developing TR-XAS using synchrotron facilities, and this method has been successfully applied to probe the dynamics of the spin crossover system (Khalil et al, 2006; Gawelda et al, 2007) and the photodissociation of ligands in NiTPP (Chen et al, 2001)
The instrument function is estimated by the pulse duration of the X-ray and modeled by a Gaussian error function with ’ 60 ps. This result indicates that the structural evolution after the 1A1 to 1MLCT excitation of the low-spin compound is complete within our time resolution

Summary

Introduction

Ultrafast time-resolved X-ray measurements such as diffraction, scattering, absorption and imaging using synchrotron radiation sources are becoming general and powerful tools for exploring structural dynamics in the fields of materials and biological sciences (Srajer et al, 1996; Collet et al, 2003; Schotte et al, 2003; Cavalleri et al, 2005; Ihee et al, 2005; Jeong et al, 2005; Gawelda et al, 2007; Ichiyanagi et al, 2007; Kong et al, 2008; Wang et al, 2008). We report the development of a TR-XAS system equipped with stable alignment of the X-ray and laser beam positions at the beamline NW14A, Photon Factory Advanced Ring, and present an example of TR-XAS measurements using these systems

X-ray and laser specifications

Pump–probe TR-XAS experiment of a spin crossover system

Concluding remarks