title: Tracking reaction dynamics in solution by pump-probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering).
abstract: Characterization of transient molecular structures formed during chemical and biological processes is essential for understanding their mechanisms and functions. Over the last decade, time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TRXAS) have emerged as powerful techniques for molecular and electronic structural analysis of photoinduced reactions in the solution phase. Both techniques make use of a pump-probe scheme that consists of (1) an optical pump pulse to initiate a photoinduced process and (2) an X-ray probe pulse to monitor changes in the molecular structure as a function of time delay between pump and probe pulses. TRXL is sensitive to changes in the global molecular structure and therefore can be used to elucidate structural changes of reacting solute molecules as well as the collective response of solvent molecules. On the other hand, TRXAS can be used to probe changes in both local geometrical and electronic structures of specific X-ray-absorbing atoms due to the element-specific nature of core-level transitions. These techniques are complementary to each other and a combination of the two methods will enhance the capability of accurately obtaining structural changes induced by photoexcitation. Here we review the principles of TRXL and TRXAS and present recent application examples of the two methods for studying chemical and biological processes in solution. Furthermore, we briefly discuss the prospect of using X-ray free electron lasers for the two techniques, which will allow us to keep track of structural dynamics on femtosecond time scales in various solution-phase molecular reactions.
authors.affiliation: Department of Chemistry, Inha University, Incheon 402-751, Republic of Korea. jkim5@inha.ac.kr.
authors.forename: Jeongho
authors.initials: J
authors.lastname: Kim
authors.affiliation: Center for Nanomaterials and Chemical Reactions, Institute for Basic Science, Daejeon, 305-701, Republic of Korea. hyotcherl.ihee@kaist.ac.kr and Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea.
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Center for Nanomaterials and Chemical Reactions, Institute for Basic Science, Daejeon, 305-701, Republic of Korea. hyotcherl.ihee@kaist.ac.kr and Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea.
authors.forename: Key Young
authors.initials: KY
authors.lastname: Oang
authors.affiliation: Ultrafast X-ray Science Lab, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Jae Hyuk
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Chemical Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea. tkkim@pusan.ac.kr.
authors.forename: Kiryong
authors.initials: K
authors.lastname: Hong
authors.affiliation: Ultrafast X-ray Science Lab, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA and Department of Chemistry and Chemical Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea. tkkim@pusan.ac.kr and Center for Inorganic Analysis, Division of Metrology for Quality of Life, Korea Research Institute of Standard and Science, Daejeon 305-340, Republic of Korea.
authors.forename: Hana
authors.initials: H
authors.lastname: Cho
authors.affiliation: Max Planck Research Department for Structural Dynamics, University of Hamburg & Center for Free Electron Laser Science, 22607 Hamburg, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Huse
authors.affiliation: Ultrafast X-ray Science Lab, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Schoenlein
authors.affiliation: Department of Chemistry and Chemical Institute for Functional Materials, Pusan National University, Busan 609-735, Republic of Korea. tkkim@pusan.ac.kr.
authors.forename: Tae Kyu
authors.initials: TK
authors.lastname: Kim
authors.affiliation: Center for Nanomaterials and Chemical Reactions, Institute for Basic Science, Daejeon, 305-701, Republic of Korea. hyotcherl.ihee@kaist.ac.kr and Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea.
authors.forename: Hyotcherl
authors.initials: H
authors.lastname: Ihee
mesh_terms: D012996:Solutions; D056928:X-Ray Absorption Spectroscopy
chemical_list: D012996:Solutions