Time Resolved Spectroscopy Using Synchrotron Radiation

Work performed at the Stanford Synchrotron Radiation Laboratory (SSRL) is reported. The timing characteristics of the SPEAR beam (pulse width less than or equal to 0.4 nsec, pulse repetition period = 780 nsec) were exploited to determine dynamic behavior of atomic, molecular, excimeric, and photodissociative gas-phase species excited by vacuum-ultraviolet (VUV) radiation. Fast fluorescence timing measurements were done to determine excited-state lifetimes of Kr and Xe. Pressure-dependent timing studies on Xe gas at higher concentrations demonstrated some of the problems associated with previous kinetic modeling of the Xe2 system. It was found that even qualitative agreement of observed Xe2 lifetimes as a function of pressure required the assumption that the radiative lifetime was a strong function of internuclear separation. The radiative decays of chemically unstable fragments, CN* (B2.sigma.) and XeF* (B2.sigma. and C2 Pi32/), were studied by pulsed photodissociation of stable parent compounds, ICN and XeF2. When the polarization of the CN* (B2.sigma./sup +/) fragment fluorescence was measured, it was found to be non-zero and strongly dependent on excitation wavelength. This polarization is related to the symmetry of the photodissociative surface via a classical model, and the variations in the polarization with wavelength is attributed to symmetry and lifetime effects of a predissociating parent molecule. Despite the drawbacks of limited availability and low radiation flux, synchrotron radiation is definitely a useful spectroscopic tool for VUV studies of gas-phase systems.

Electron synchrotron storage rings, such as the VUV ring at the National Synchrotron Light Source (NSLS), produce short pulses of infrared (IR) radiation suitable for investigating the time-dependent phenomena in a variety of interesting experimental systems. In contrast to other pulses sources of IR, the synchrotron produces a continuum spectral output over the entire IR (and beyond), though at power levels typically below those obtained from laser systems. The infrared synchrotron radiation (IRSR) source is therefore well-suited as a probe using standard FTIR spectroscopic techniques. Here the authors describe the pump-probe spectroscopy facility being established at the NSLS and demonstrate the technique by measuring the photocarrier decay in a semiconductor.

At the time that the editors conceived the idea of trying to organize the meeting on which the contents of this volume are based and which became, in March 1980, a NATO Advanced Study Institute, the techniques of time-resolved fluorescence spectroscopy, in both the nanosecond and sub-nanosecond time-domains, might reasonably have been said to be coming of age, both in their execution and in the analysis and interpretation of the results obtained. These techniques, then as now, comprised mainly a number of pulse methods using laser, flash-lamp or, most recently, synchrotron radiation. In addition, significant developments in the more classical phase approach had also rendered that method popular, utilizing either modulation of an otherwise continuous source or, again recently, the ultra-rapid pulse rate attainable with a synchrotron source. In general terms, time-resolved fluorescence studies are capable, under appropriate conditions, of supplying direct kinetic information on both photophysics and various aspects of molecular, macromolecular and supramolecular structure and dynamics. The nanosecond and sub-nanosecond time-scales directly probed render these techniques particularly appropriate in studying relaxation and fluctuation processes in macromolecules, particularly biopolymers (e. g. proteins, nucleic acids), in supramolecular assemblies such as cell membranes, and in a variety of relatively simpler model systems.

The development of synchrotron radiation (SR) as a research tool was driven largely by the needs of materials scientists and solid-state physi cists. However, the availability of SR has extended significantly the capa bility of scientists who study biological structure with radiation. This volume contains some of the results reported at a symposium held at Brookhaven National Laboratory in May 1988 to discuss the application of synchrotron radiation to structural biology. We are grateful for financial support from the u. s. Department of Energy, the National Institutes of Health, Genentech, Inc., Blake Indus tries, Inc., Evans and Sutherland Co., The Upjohn Company, Eli Lilly and Company, Enraf-Nonius Service Corp., and Associated Universities, Inc. We warmly thank Ms. Nancy Siemon for her tireless efforts with correspondence and the manuscripts for this symposium volume. Symposium Committee: Robert M. Sweet, Chair Malcolm S. Capel Benno P. Schoenborn John C. Sutherland Elizabeth C. Theil Stephen W. White Avril D. Woodhead Helen Z. Kondratuk, Coordinator v CONTENTS An Introduction to the Symposium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 R. M. Sweet SYMPOSIUM LECTURE Developments in X-ray Technology and Their Contribution to Structural Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 H. E. Huxley SOME OF THE SYNCHROTRON FACILITIES FOR BIOLOGICAL STRUCTURAL STUDIES MacChess - A Macromolecular Diffraction Resource at the Cornell High Energy Synchrotron Source . . . . . . . . . . . . . . . . . . . 15 W. Schi1dkamp, K. Moffat, B. Batterman, D. Bilderback, T-Y. Teng, A. LeGrand and D. Szebenyi Facilities Available for Biophysics Research at the Stanford Synchrotron Radiation Laboratory. . . . . . . . . . . . . . . . . . . . . 19 R. P."

Hardly any other discovery of the nineteenth century did have such an impact on science and technology as Wilhelm Conrad Röntgen’s seminal find of the X-rays. X-ray tubes soon made their way as excellent instruments for numerous applications in medicine, biology, materials science and testing, chemistry and public security. Developing new radiation sources with higher brilliance and much extended spectral range resulted in stunning developments like the electron synchrotron and electron storage ring and the freeelectron laser. This handbook highlights these developments in fifty chapters. The reader is given not only an inside view of exciting science areas but also of design concepts for the most advanced light sources. The theory of synchrotron radiation and of the freeelectron laser, design examples and the technology basis are presented. The handbook presents advanced concepts like seeding and harmonic generation, the booming field of Terahertz radiation sources and upcoming brilliant light sources driven by laser-plasma accelerators. The applications of the most advanced light sources and the advent of nanobeams and fully coherent x-rays allow experiments from which scientists in the past could not even dream. Examples are the diffraction with nanometer resolution, imaging with a full 3D reconstruction of the object from a diffraction pattern, measuring the disorder in liquids with high spatial and temporal resolution. The 20th century was dedicated to the development and improvement of synchrotron light sources with an ever ongoing increase of brilliance. With ultrahigh brilliance sources, the 21st century will be the century of x-ray lasers and their applications. Thus, we are already close to the dream of condensed matter and biophysics: imaging single (macro)molecules and measuring their dynamics on the femtosecond timescale to produce movies with atomic resolution.

This book has grown out of our shared experience in the development of the Stanford Synchrotron Radiation Laboratory (SSRL), based on the electron-positron storage ring SPEAR at the Stanford Linear Accelerator Center (SLAC) starting in Summer, 1973. The immense potential of the photon beam from SPEAR became obvious as soon as experiments using the beam started to run in May, 1974. The rapid growth of interest in using the beam since that time and the growth of other facilities using high-energy storage rings (see Chapters 1 and 3) demonstrates how the users of this source of radiation are finding applications in an increasingly wide variety of fields of science and technology. In assembling the list of authors for this book, we have tried to cover as many of the applications of synchrotron radiation, both realized already or in the process of realization, as we can. Inevitably, there are omissions both through lack of space and because many projects are at an early stage. We thank the authors for their efforts and cooperation in producing what we believe is the most comprehensive treatment of synchrotron radiation research to date.