Impact Objectives

• Exploit multiple X-ray spectroscopic techniques, and unravel the complexity of interplay between electronic and structural dynamics

• Perform the Kb X-ray emission spectroscopy (XES), analyse the splitting of two peaks and gain new information about the spin flip from singlet to triplet states

Shining a brilliant X-ray laser on transient states

Dr Tetsuo Katayama, from the Japan Synchrotron Radiation Research Institute, discusses his work on X-ray emission spectroscopy

What type of Can you talk a little about your own research XAS spectrum of different types of research is background? How did you come to be materials. Since completing these initial underway at the involved in this field? measurements, we are now undertaking Japan Synchrotron a series of X-ray emission spectroscopies Radiation Research I have always been interested in exploring (XES). Institute (JASRI)? the properties of materials through spectroscopy. Since 2012, I have been With this technique, we detect the X-rays JASRI is a public working on developing new techniques emitted by molecules after they have interest foundation that was incorporated in for ultrafast experiments using SACLA absorbed the incident X-ray. We focus 1990 to promote the use of its synchrotron XFEL beamlines. For example, the XFEL particularly on the 3p to 1s transition, radiation facilities. Its goal is to promote diagnostic system to compensate for the which is known as the Kb XES spectrum. and support innovations in science and timing jitter between XFEL and optical laser The Kb XES spectral line of 3d transition technology. We operate, maintain and is essential for this project if we hope to metals splits into two peaks owing to the manage accelerators and photon beamlines, achieve high time resolution (of around p-d exchange interaction. As the number and provide support for users of the 70 femtoseconds). My experiences with of unpaired 3d electrons increases, the Spring-8 synchrotron radiation facilities as these systems have motivated me to start split between the two peaks becomes well as the X-ray free electron laser SACLA. this study, to see, for example, how much broader. Our goal is to measure the Kb The Institute comprises a number of detailed structural information of nuclear XES spectrum, to analyse the splitting of divisions, each responsible for and focused wave packets can be obtained with X-ray two peaks and to gain information about on different areas of radiation research, spectroscopy? This question comes from intersystem crossing. This intersystem including the light source division, the my curiosity in consideration of whether cross refers to the radiation-less transition protein crystal analysis division and the ultrafast X-ray spectroscopy contributes to between two electronic states with different diffraction and scattering division. femtochemistry. spin multiplicity. Ultimately, if our research technique is applied to design photo- Within our own group, in our current Can you explain in lay-person terms the functional materials, such as photocatalysis, project, we have used X-ray absorption research you are currently undertaking into it is very exciting. spectroscopy (XAS), which is sensitive, both ultrafast time-resolved X-ray spectroscopies? to the unoccupied electronic structure and What are you hoping to achieve? Are there any results you have seen that you to the local structure of the absorbing atom. are particularly pleased with? We are currently trying to perform X-ray In this work, we are measuring the emission spectroscopy, which is sensitive to ratio of the X-ray intensity of a sample We were very happy when the wavepacket the spin state of the central metal ion. We by the amount it absorbs with respect is observed at the pre-edge energy position, hope that this may help us to uncover new to the incident beam. This is known as corresponding to the 1s->3d transition. information about the spin flip from singlet the absorbance of the given material. This transition is very weak but contains to triplet states (intersystem crossing). By measuring the absorbance at each very important information about the wavelength, we are able to obtain the structure. l

10 www.impact.pub Capturing molecular motions with the (ultra)fast X-ray spectroscopy

An international inter-disciplinary research team, led by Dr Tetsuo Katayama from the JASRI, seeks to film ground-breaking footage of ultrafast physical and electronic changes of photoreactions at an atomic level using X-ray free-electron lasers

Spectroscopy, the study of the interaction chemical reactions,’ Katayama explains. ‘In this work, we have demonstrated the ability between matter and electromagnetic ‘This ability is highly useful to achieve a to observe structural changes and to create radiation, is used in chemistry, physics, comprehensive understanding about how the a molecular ‘movie’ with an atomic-level astronomy and other fields, and allows molecular ensemble propagates on the multi- resolution,’ highlights Katayama. ‘I believe scientists to investigate the physical and dimensional potential energy surface.’ this ability will be highly useful in finding out electronic structure as well as composition what nuclear motions are triggering bond of materials. A number of techniques, In time-resolved X-ray absorption dissociations or formations.’ Such key steps including atomic spectroscopy and electron spectroscopy, it is now possible to selectively in photoreaction are not yet detected, but the spectroscopy, have been developed to detect trace ultrafast changes in local molecular group’s breakthroughs are a major step on and measure materials in this way. structure by element, and this is anticipated the way to being able to see and record more to lead to exciting new advances in our major events in photoreactions. Dr Tetsuo Katayama, from the Japan understanding of molecular structure and the Synchrotron Radiation Research Institute changes wrought during chemical reactions. The researchers used the SPring-8 Angstrom (JASRI), is an expert in this field. He ‘X-ray free electron lasers with femtosecond Compact free electron Laser (SACLA) XFEL explains that free-electron lasers (FELs) are duration are a tool that brings a new evolution to measure femtosecond time-resolved XAS. wavelength-tunable lasers generated from to femtosecond chemistry,’ says Katayama. An optical laser was used for the pump pulse extremely high-speed electrons that move ‘In this study, the local structural changes to initiate the photoreactions, while XFEL freely through a periodic magnetic structure, of nuclear wavepacket oscillations that was used for the probe pulse to measure allowing it to work across the widest range occur when the photoexcited metal complex the structural change during the relaxation of frequency of any type of laser. ‘They can relaxes in solution are observed with atomic process. SACLA is housed next to the SPring-8 operate at wavelengths from microwaves, resolution.’ By pairing timing fluctuation synchrotron radiation facility owned by through infrared and terahertz radiation, correction technology with the data provided RIKEN and run by JASRI. ‘A copper-based including the visible spectrum as well as using XFELs, he and his team hope to photoexcited metal complex, [Cu(2,9-dimethyl- X-rays and UV,’ he shares. Used in X-ray produce a real-time recording of molecular 1,10-phenanthroline)2]+, was subjected to absorption spectroscopy (XAS), they offer structure with a time resolution of just 50 the pump pulse to generate oscillations and exciting capabilities for researchers. Katayama femtoseconds. to the probe pulse to record them,’ explains uses X-Ray free-electron lasers (XFELs) in Katayama. ‘Three types of nuclear wave his work. ‘The advent of XFELs provides SECRETS UNLOCKED packet oscillations were observed during unprecedented research opportunities,’ Katayama is optimistic that his group’s work the relaxation stage: a breathing motion he enthuses. They have allowed scientists will showcase exciting developments in the associated with the stretching and shrinking to overcome the difficulties experienced field of X-ray spectroscopy. ‘This work has of the copper-nitrogen bond lengths, and two in extending knowledge on the molecular demonstrated that X-ray spectroscopies can vibration motions resulting from changes structure of materials at an atomic level. The capture not only the symmetric breathing in the bond angles between the copper and development of optical lasers has pushed the mode, but also the symmetry-breaking nitrogen atoms.’ He clarifies that the lifetimes boundaries of photochemistry, and it is now modes.’ He and his team have unlocked the of these oscillations were found to vary, and becoming possible to detect the molecular secrets of how XAS gains its sensitivity to the bending vibrations have been strongly structure of materials with atomic-level individual nuclear motion. Not only is this an associated with the characteristic structural spatio-temporal resolution. ‘This means exciting finding in its own right, but it will also flattening of the molecular complex. that it is possible to investigate molecular contribute to future research on tracking the structures during ultrafast nonadiabatic structural changes of different molecules.

www.impact.pub 11 TIME BARRIERS BROKEN decide about what to do,’ he outlines. In Project Insights ‘XFELs push time-resolved X-ray spectroscopy these instances, the power of collaborations into the ultrafast femtosecond regime,’ demonstrates its strengths as colleagues from FUNDING explains Katayama. This essentially means other institutions and fields can lend their • JSPS KAKENHI Grant Numbers that it has become possible to detect and expertise. ‘Fortunately, I could discuss with JP17H06141, JP19H05782, and JP19H04407 record reactions that occur in femtoseconds experienced collaborators who had a variety of • EPSRC (EP/R021503/1) and Leverhulme Trust (RPG-2016-103) – each femtosecond being one millionth backgrounds,’ he says. ‘Their inputs were very • ‘Lendület’ (Momentum) Program of the of a billionth of a second. His work helpful to make the experiments successful.’ Hungarian Academy of Sciences (LP2013-59) highlights the benefits of ultrafast X-ray • The Government of Hungary and the spectroscopy, demonstrating how it is truly BOUNDARIES PUSHED European Regional Development Fund complementary to ultrafast femtosecond Collaboration is a major part of this research under grant VEKOP-2.3.2-16-2017-00015, optical spectroscopies as well as offering and it not only helps drive new ideas and the National Research, Development useful features in the creation of molecular but also helps in overcoming challenges and Innovation Fund (NKFIH FK 124460) • The National Science Center (NCN) in films that are unmatched in their precision. encountered during projects. In addition Poland under SONATA BIS 6 grant No. This is not only an incredible development to these benefits highlighted by Katayama, 2016/22/E/ST4/00543 in terms of furthering our knowledge of what he also outlines other ways in which his • The German Cluster of Excellence CUI: truly happens at a molecular level during partners have contributed to the progress of Advanced Imaging of Matter (AIM) these reactions, but also helps other scientists the project on tracking nuclear wave packet who use optical lasers. oscillations. ‘The inputs from all of the COLLABORATORS collaborators on this project are invaluable • Thomas Northey • Wojciech Gawelda With XFELs being an incredibly rare resource in promoting the full gamut of scientific • Christopher J Milne – there are only five facilities in existence activities, including experimental planning, • György Vankó worldwide – access to them is very limited. measurement, analysis, interpretation of data • Frederico A Lima Thus, typically, each team is only able to and publication,’ he states. Scientists from • Rok Bohinc perform an experiment twice a year and it is key institutions around the world, including • Zoltán Németh vital that careful planning is put into place European-XFEL, Swiss-FEL, Newcastle • Shunsuke Nozawa ahead of time to maximise each opportunity University, the Hungarian Academy of • Tokushi Sato • Dmitry Khakhulin • Jakub Szlachetko We have demonstrated the ability to observe structural • Tadashi Togashi • Shigeki Owada changes and to create a molecular ‘movie’ with an • Shin-ichi Adachi • Christian Bressler atomic-level resolution • Makina Yabashi • Thomas J Penfold • Tae Kyu Choi to use the equipment. This raises significant Sciences, KEK (the High Energy Accelerator challenges to teams working with the XFELs, Research Organization), DESY (Deutsches CONTACT DETAILS and Katayama’s group was no exception. Elektronen-Synchrotron) and the Polish Dr Tetsuo Katayama ‘During the experiments, I experienced Academy of Sciences, have all contributed to many unexpected issues and needed to this collaboration. l T: +81 791 58 0802 (3220) E: [email protected] W: https://researchmap.jp/ tetsuokatayama?lang=en

BIO Dr Tetsuo Katayama received his PhD from The University of Tokyo in 2010. From 2010 until 2012, Katayama worked for Linac Coherent Light Source (LCLS) XFEL exploring the surface chemical reaction. From 2012, he has worked on ultrafast X-ray experiments at SPring-8 Angstrom Compact LAser (SACLA) XFEL.

A schematic view of potential energy surface and molecular trajectory during the photoreaction of the copper complex

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