X-Ray Absorption Spectroscopy of Gas Phase Metal Clusters.

The production and control of vapor phase metal clusters in sizes ranging from one to thousands of atoms is discussed. Electron yield detection has a very high sensitivity to species in the gas phases. These events suggested the possibility of a combined experiment in-situ x-ray absorption study of evaporated metal in gas phase. The comparison of gas phase results to earlier work on supported metal catalysis would be very helpful in determining the extent of support interaction. In addition, new information gathered from experiments where gas phase metal atoms or clusters are reacted with molecules, such as H2O, Cl, NH3 etc., would improve our understanding of transition metal coordination chemistry. Trial experiments were completed at SSRL using a preliminary design for the metal vapor celldetector. A resistance heated evaporation source was positioned so that metal vapor in this case Cu would flow directly through the electron detection grids, while the x-ray beam crossed through the vapor between the grids. The results suggested some improvements to the evaporator design which would result in better electrical isolation and less contamination of insulators. The newer design will also have better vacuum pumping characteristics and a longer path for x-rays through the vapor.