Time-resolved XAFS of a molecular excited state and glass-capillary concentration of x-rays

Two x-ray techniques are presented. One is a new spectroscopic method to study changes in molecular structure upon laser excitation. X-ray absorption fine structure (XAFS) has been combined with rapid-flow laser spectroscopy to achieve new insight into the structure of the lowest triplet state of tetrakis(pyrophosphito) diplatinate(II), {dollar}rm Ptsb2(Psb2Osb5Hsb2)sbsp{lcub}4{rcub}{lcub}4-{rcub}.{dollar} The phosphorous planes are found to contract along the Pt-Pt axis by 0.52 {dollar}pm{dollar} 0.16 A in response to the laser excitation. This experiment, which is the first {dollar}mu{dollar}sec-resolved XAFS measurement, has given unprecedented structural detail of a molecule excited to a short-lived electronic state.; The other technique is a new method to concentrate, or "focus", a collimated x-ray beam. Unlike standard x-ray focusing methods, this method consists of using the inner wall of a tapered glass capillary to guide the x rays down the bore of the capillary by multiple total external reflections at the air/glass interface. The x-ray beam emerging from the capillary is compressed to a size given by the size of the bore at the tip of the capillary. A variety of tapered capillaries have been fabricated with exit bore sizes ranging from 0.1 {dollar}mu{dollar}m to 100 {dollar}mu{dollar}m. The methods used in fabricating and characterizing the concentrators are presented along with the measured x-ray intensity enhancements due to the devices. In addition, the results of various applications of these x-ray concentrators are reported including an XAFS measurement, an imaging experiment, and a beam-steering technique. The most significant part of this research has been the generation of submicron diameter x-ray beams with intensity enhancements greater than 100. This method is the only method presently available to produce such x-ray beams. Finally, a ray-tracing program has been developed which calculates the paths of the meridional rays passing through the two-dimensional profile of any channel including the irregular figures of the tapered glass capillaries. Using the calculated angles of incidence and the physical properties of the glass, the reflection coefficients for each bounce may be calculated and the x-ray transmission of the capillary predicted.