title: Femtosecond X-ray absorption spectroscopy at a hard X-ray free electron laser: application to spin crossover dynamics.
abstract: X-ray free electron lasers (XFELs) deliver short (<100 fs) and intense (∼10(12) photons) pulses of hard X-rays, making them excellent sources for time-resolved studies. Here we show that, despite the inherent instabilities of current (SASE based) XFELs, they can be used for measuring high-quality X-ray absorption data and we report femtosecond time-resolved X-ray absorption near-edge spectroscopy (XANES) measurements of a spin-crossover system, iron(II) tris(2,2'-bipyridine) in water. The data indicate that the low-spin to high-spin transition can be modeled by single-exponential kinetics convoluted with the overall time resolution. The resulting time constant is ∼160 fs.
authors.affiliation: LCLS, SLAC National Laboratory, Menlo Park, California 94025, United States.
authors.forename: Henrik T
authors.initials: HT
authors.lastname: Lemke
authors.forename: Christian
authors.initials: C
authors.lastname: Bressler
authors.forename: Lin X
authors.initials: LX
authors.lastname: Chen
authors.forename: David M
authors.initials: DM
authors.lastname: Fritz
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Gaffney
authors.forename: Andreas
authors.initials: A
authors.lastname: Galler
authors.forename: Wojciech
authors.initials: W
authors.lastname: Gawelda
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Haldrup
authors.forename: Robert W
authors.initials: RW
authors.lastname: Hartsock
authors.forename: Hyotcherl
authors.initials: H
authors.lastname: Ihee
authors.forename: Jeongho
authors.initials: J
authors.lastname: Kim
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.forename: Jae Hyuk
authors.initials: JH
authors.lastname: Lee
authors.forename: Martin M
authors.initials: MM
authors.lastname: Nielsen
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Stickrath
authors.forename: Wenkai
authors.initials: W
authors.lastname: Zhang
authors.forename: Diling
authors.initials: D
authors.lastname: Zhu
authors.forename: Marco
authors.initials: M
authors.lastname: Cammarata