Ethene Spectrum Measured at
Fundamental Limits of Resolution
In an experiment conducted at Beamline 9.0.1 before its move to Sector 10, T. Darrah Thomas's group from Oregon State University explored the electronic structure of ethene via photoelectron spectroscopy. Their carbon 1s measurements have an overall experimental resolution of 55 meV, with no additional information expected from further improvements in resolution because the natural linewidths of ethene's carbon 1s hole states are 90-100 meV. The measured spectrum conforms very well to a model of core-ionized ethene in which the core hole vacated by the ejected photoelectron is localized to one carbon or the other.
In the figure above, the gray error bars represent the measured spectrum of ethene. The red curve is the spectrum calculated on the basis of a localized core hole, along with other appropriate theoretical assumptions, and dispersed to show the combined effects of experimental resolution, lifetime broadening, and post-collision interaction. (PCI occurs when an Auger electron, emitted after photoionization, overtakes the photoelectron. This exposes the photoelectron to an increased net nuclear change, which influences its detected energy.) The ab initio calculations are in excellent agreement with the experimental data, an encouraging sign in the evolution of successful theory on ethene. The blue, vertical bars indicate 14 of the predicted vibrational transitions, and several are labeled with the appropriate vibrational quantum numbers.
Research conducted by J. Bozek (Berkeley Lab), T.X. Carroll (Keuka College), J. Hahne (Oregon State University), L.J. Saethre (University of Bergen, Norway), J. True (OSU), and T.D. Thomas (principal investigator, OSU), using the spherical-sector electrostatic analyzer at Beamline 9.0.1.
Funding: Office of Basic Energy Sciences of the U.S. Department of Energy, National Science Foundation (Grant No. CHE-94083868), and the Research Council of Norway.
Publications about this experiment:
J. Bozek, T.X. Carroll, J. Hahne, L.J. Saethre, J. True, and T.D. Thomas, Phys. Rev. A 57, 157 (1998).
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