Accessible light sources

Chemiluminescence has been studied extensively (2) for several reasons (/) chemiexcitation relates to fundamental molecular interactions and transformations and its study provides access to basic elements of reaction mechanisms and molecular properties (2) efficient chemiluminescence can provide an emergency or portable light source (J) chemiluminescence provides means to detect and measure trace elements and pollutants for environmental control, or clinically important substances (eg, metaboHtes, specific proteins, cancer markers, hormones, DNA) and (4) classification of the hioluminescent relationship between different organisms defines their biological relationship and pattern of evolution. 

These examples should have illustrated the importance of lasers as powerful tools in elucidating many details of photochemical processes which are not accessible with conventional light sources. 

The photochemistry of triphenylmethyl radicals in solution has been of interest for some time because the relatively long lifetimes of these species (some are essentially stable) have made their study accessible with low-intensity light sources. Relatively recently, laser flash photolysis has been used to confirm the tendency of the excited radicals to undergo ring closure to form the 9-phenyldihydro-fluorenyl radicals. 

LCLS, Linac coherent light source website. LCLS, Menlo Park, CA (see http //www-ssrl.slac.stanford.edu/lcls/, last accessed 03 September 2006)... 

The metal-polymer studies were done in collaboration with C.A. Kovac, M.J. Goldberg, J.F. Morar and R.A. Poliak. The polymer-metal studies were done in collaboration with S.P. Kowalczyk. I wish to thank J. Stohr and A. Hitchcock for many enlightening discussions on NEXAFS techniques and interpretation and for timely access to their data throughout the course of these studies. Research was carried out in part at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences. 

A comprehensive list of the world s synchrotron radiation sources, including many still on the drawing boards, can be found at many of the web-sites maintained by the Light Sources (e.g. http //www.nsls.bnl.gov/AccPhys/synchros.htm). Table 1 provides the web addresses for some synchrotron facilities. These sites provide up to date information on characteristics of the beams provided, key experimental expertise, future construction plans, and resources for users including how to obtain access. 

National Synchrotron Light Source at the Brookhaven National Laboratory,http // www.nsls.bnl.gov/facility/ (accessed 14 June 2011). 

Fluorescence can be resolved overtime. The use of very short pulsed light sources (picosecond lasers and laser diodes) has rendered accessible graphs of fluorescence decay as a function of the time. New applications based upon a greater knowledge of the lifetime are under development, although they are still not used much in chemical analysis. 

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