Toward Femtosecond X-ray Spectroscopy at the Advanced Light Source

Thesis/Dissertation · Thu Jan 01 00:00:00 EST 2004

DOI:https://doi.org/10.2172/828144· OSTI ID:828144

Chong, Henry Herng Wei ^[1]

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1. Univ. of California, Berkeley, CA (United States)

The realization of tunable, ultrashort pulse x-ray sources promises to open new venues of science and to shed new light on long-standing problems in condensed matter physics and chemistry. Fundamentally new information can now be accessed. Used in a pump-probe spectroscopy, ultrashort x-ray pulses provide a means to monitor atomic rearrangement and changes in electronic structure in condensed-matter and chemical systems on the physically-limiting time-scales of atomic motion. This opens the way for the study of fast structural dynamics and the role they play in phase transitions, chemical reactions and the emergence of exotic properties in materials with strongly interacting degrees of freedom. The ultrashort pulse x-ray source developed at the Advanced Light Source at the Lawrence Berkeley Laboratory is based on electron slicing in storage rings, and generates ~100 femtosecond pulses of synchrotron radiation spanning wavelengths from the far-infrared to the hard x-ray region of the electromagnetic spectrum. The tunability of the source allows for the adaptation of a broad range of static x-ray spectroscopies to useful pump-probe measurements. Initial experiments are attempted on transition metal complexes that exhibit relatively large structural changes upon photo-excitation and which have excited-state evolution determined by strongly interacting structural, electronic and magnetic degrees of freedom. Specifically, iron(II) complexes undergo a spin-crossover transition upon optical irradiation. The dynamics of the transition involve a metal-to-ligand charge transfer, a ΔS=2 change in magnetic moment and 10% bond dilation in the first coordination shell of the iron. Studies of the electronic dynamics are studied with time-resolved optical absorption measurements. The current progress of time-resolved structural studies to complete the picture of the spin-crossover transition is presented.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 828144
• Report Number(s): LBNL-55971; R&D Project: 505801; TRN: US0403848
• Resource Relation: Other Information: TH: Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); PBD: 16 Apr 2004
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
47 OTHER INSTRUMENTATION
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ADVANCED LIGHT SOURCE
CHEMICAL REACTIONS
DEGREES OF FREEDOM
ELECTRONIC STRUCTURE
LAWRENCE BERKELEY LABORATORY
MAGNETIC MOMENTS
SPECTROSCOPY
STORAGE RINGS
SYNCHROTRON RADIATION
TRANSITION ELEMENTS
X-RAY SOURCES
X-RAY SPECTROSCOPY
ULTRAFAST X-RAY SPECTROSCOPY TRANSITION METAL CHEMISTRY SYNCHROTRONS LASERS