1. SYMMETRY RESOLUTION YIELDS EVIDENCE FOR SHAPE RESONANCE
by Lori Tamura
(Contact: darrah.thomas@orst.edu)

Symmetry-resolved photoelectron spectroscopy measurements taken at the ALS have provided the first convincing evidence for the existence of a shape resonance in acetylene, 15 years after the shape resonance was first proposed.

Shape resonances occur when photoelectrons are temporarily trapped by a potential energy barrier in the molecule. Because the shape of the potential depends upon the configuration of the molecule, it was initially thought that shape resonances might be a simple way to obtain information about molecular geometry. In particular, it was thought that the energy at which a shape resonance occurred could be correlated with the length of molecular bonds.

An attempt was made 15 years ago to quantify the relationship between shape-resonance energy and bond length for a number of molecules, including acetylene. However, shape resonances are manifested as broad, somewhat ambiguous peaks in the photoelectron cross section, and the criteria for identifying shape resonances in general were unclear. Subsequent studies found only weak evidence for a shape resonance in acetylene.

The high brightness of the ALS photon beam and the high resolution afforded by Beamline 10.0.1 (formerly Beamline 9.0.1) allowed T. D. Thomas of Oregon State University and his colleagues to see features of the photoelectron spectrum that were not readily apparent in previous work. At the ALS, the researchers were able to resolve the carbon 1s peak of acetylene into contributions from electrons of g (symmetric) and u (antisymmetric) character. (A highlight of this work can be viewed on the Web at http://www-als.lbl.gov/als/science/sci_archive/shres2.html.)

According to dipole selection rules, transitions to the shape resonance can result only from ionization involving electrons of g character. Analysis of the symmetry-resolved data showed that the cross section for ionization of g-character electrons goes through a maximum at an incident photon energy of about 317 eV, coinciding with the location of the shape resonance indicated by previous investigations and slightly higher than that predicted by theory. These results also provide a test of calculations of the photoionization cross section near the photoionization threshold for both u and g ionization. The researchers found that the theory successfully reproduces the trend of the data, indicating that most of the basic physics has been included.

Although prospects for the original "molecular bond ruler" concept appear to be dim because of the difficulty involved in identifying shape resonances and because of the complexity of the correlation (if any), this result clearly demonstrates how the improvements in spectral resolution made possible by the ALS can help resolve outstanding questions in the scientific literature and lead to better understanding of the inner workings of molecules.

Research conducted by T.D. Thomas and J. Hahne (Oregon State University); N. Berrah (Western Michigan University); E. Kukk (Western Michigan University and Berkeley Lab); J. Bozek (Berkeley Lab); T.X. Carroll (Keuka College); and T. Karlsen and L.J. Saethre (University of Bergen, Norway), using Beamline 10.0.1.

Funding: U.S. Department of Energy, Office of Basic Energy Sciences; National Science Foundation; Research Council of Norway.

Publication about this experiment: T.D. Thomas et al., Phys. Rev. Lett. 82, 1120 (1999).

2. ANNUAL ALS USERS' ASSOCIATION MEETING FEATURES A WORLD OF SCIENCE
by Art Robinson
(Contact: kevan@oregon.uoregon.edu)

Science took the front seat as 219 ALS users and staff gathered on Monday and Tuesday, October 18 and 19, for the annual users' meeting. Packed into two busy days were 31 invited oral presentations and 80 submitted poster presentations, as well as time to visit 24 vendor booths.

Monday morning opened with a welcome from Berkeley Lab Director Charles Shank. DOE Associate Director for Basic Energy Sciences Patricia Dehmer spoke of impressive progress at the ALS and an upcoming review of the ALS that may lead to increased funding. ALS Director Daniel Chemla provided a detailed overview of planning for new beamlines and endstations to conduct twenty-first-century science at the ALS, as well as a breakdown of how the facility spends the money it currently has. After UEC Chair Steve Kevan conducted a brief user business meeting, CXRO Director David Attwood contributed a moving remembrance of CXRO colleague and former UEC Chair Werner Meyer-Ilse, who died last summer (see ALSNews Vol. 132, July 21, 1999). The remainder of the meeting was given over to reports on science at the ALS with sessions dedicated to environmental science, chemical dynamics, biosciences, magnetic materials, and atomic and molecular science. In addition, there was an ALS highlights session that emphasized new results and a session comprising highlights from the young scientists who will carry the ALS into the future.

Awards took center stage at the Monday night banquet, held this year at the University of California, Berkeley, men's faculty club. The Halbach Award for Outstanding Instrumentation at the ALS went to Simone Anders, Rob Duarte, Greg Morrison, Howard Padmore (all of the ALS), and Mike Scheinfein (Arizona State University) for development of the PEEM2 photoemission electron microscope. The Tim Renner User Services Award was given to the members of the ALS User Services Office (Ruth Pepe, Bernie Dixon, Sharon Fujimura, Jane Tanamachi, and Barbara Phillips). Greg Denbeaux (CXRO) won the second annual student poster competition with his presentation describing spectromicroscopy capabilities of the x-ray microscope (XM-1) on Beamline 6.1.2. Roland Kawakami, Z.-Q. Qiu (both of the University of California, Berkeley), and Eli Rotenberg (ALS) received the David A. Shirley Award for Outstanding Scientific Achievement at the ALS for their work in fabricating novel multilayer magnetic quantum well samples and using photoelectron spectroscopy to measure their fundamental properties.

On the Wednesday after the users' meeting, two day-long workshops captured much interest. Many of the world's experts in the field gathered to discuss Future Directions in Ultra-High-Resolution Spectroscopy for the Study of Complex and Correlated Phenomena. Based on the workshop proceedings, organizers Dan Dessau (University of Colorado) and Z.-Q. Qiu (University of California, Berkeley) hope to have a proposal ready for submission by the end of the year for an elliptically polarized undulator beamline. Organized by Mike Martin and Wayne McKinney (ALS), the second workshop, titled "A Far-Infrared Beamline at the ALS: Future Prospects," explored the possibilities of establishing a synchrotron-based far-infrared (far-IR) program at the ALS. Topics included various methods for extracting far-IR from the storage ring and research areas that could be enhanced by such a beamline.

3. LATEST MILESTONES FOR EPU BEAMLINE
(Contact: ATYoung@lbl.gov)

Beamline 4.0.1-2, home of the ALS's first elliptically polarizing undulator (EPU), has recently reached a couple of significant milestones. At the October 12 ALS Experimental Systems Group meeting, project leader Tony Young reported that the beamline's monochromator is now installed and that light produced by the EPU has been directed through the branchline to the endstation system. The new monochromator utilizes a variable-included-angle, plane-grating design that will provide investigators with the flexibility of a wide photon energy range, from 60 to 2000 eV with the current 5-cm-period undulator. The EPU will deliver high-flux polarized x rays of linear, elliptical, or circular polarization for performing high-resolution spectroscopy of magnetic materials.

At the same meeting, Gyorgy Snell, a member of a research group led by Nora Berrah (Western Michigan University), reported on the beamline's first experimental results, obtained before installation of the monochromator. The researchers performed spin-resolved Auger spectroscopy of xenon, krypton, and argon and determined the magnetic dipole moment of the Xe 4d^-1, Kr 3d^-1 and Ar 2p^-1 states over a broad energy range. Because these measurements required circularly polarized light of high intensity but not high spectral resolution, they were done before the monochromator was installed, taking advantage of the intense fundamental of the undulator beam.

The EPU project team is currently commissioning the beamline by calibrating the beam's energy, optimizing its spectral resolution, and characterizing its polarization.

4. MACROMOLECULAR CRYSTALLOGRAPHY BEAMTIME ALLOCATED
(Contact: GFKrebs@lbl.gov)

The Proposal Study Panel for the Macromolecular Crystallography Facility at the ALS has finalized beamtime allocations for the January to June 2000 running period. The majority of crystallography proposals this period were deemed to be of very high scientific caliber by the panel. Unfortunately, many excellent proposals had to be turned down due to high demand and the short running period. (A shutdown is scheduled for mid-February to mid-March.) The panel studied 70 proposals requesting a total of 425 eight-hour shifts. The facility has 148 shifts to allocate to independent investigators, so only 35% of the requested beamtime could be granted. Twenty-four proposals were awarded beamtime. The average score was 2.3, and the cutoff score was 1.92. For more information about the selection process and results, see the proposal scores Web site at http://www-als.lbl.gov/als/quickguide/pspscores_mcf.html.

5. ICESS8 SPECTROSCOPY CONFERENCE ON THE WEB
(Contact: icess@lbl.gov)

Information about the Eighth International Conference on Electronic Spectroscopy and Structure (formerly the International Conference on Electron Spectroscopy) is now available on the Web at http://www-als.lbl.gov/icess. The conference, sponsored in part by the ALS, is to be held at the Clark Kerr Campus of the University of California, Berkeley, on August 8-12, 2000. Anyone interested in receiving mailings for the conference is encouraged to go to the site and fill out the on-line interest form by December 15.

6. UEC CORNER: NOTES FROM THE USERS' EXECUTIVE COMMITTEE
by Stephen Kevan
(Contact: kevan@oregon.uoregon.edu)

It was good to see so many users and so much enthusiasm at the ALS Users' Meeting last week. Thanks to all of you who attended for making it a great meeting. This year's meeting demonstrated that the ALS is clearly entering a very productive and exciting phase of operation. I am already looking forward to the coming year at the ALS and to all the great science that will be presented at the next users' meeting.

I want to make sure that I clear up one misunderstanding that became apparent during our brief meeting with officials from the DOE. Some had understood that there has been a movement toward some sort of "Program Independent Investigator" status that would entail allocating significant blocks of future time to some independent investigators. The only changes that have been made, and the only changes that are likely to be made, to the independent investigator program are that (1) proposals now stay active for two years after submission as long as the investigator submits an Experiment Report/Beamtime Request every six months and (2) proposal ratings are provided to investigators so that they will have some indication of the likelihood of beamtime being allocated over the two-year period. Representatives from the UEC, the Proposal Study Panel, and the ALS all agreed that a Program Independent Investigator program could seriously damage the development and viability of the Participating Research Teams that are so vital to the future of the ALS.

I remind you that we will be replacing some members of the UEC with a mail-in ballot in a few weeks. It is not too late to nominate new members; contact Art Robinson (ALRobinson@lbl.gov) for details.

Finally, I want to tell you that in the next few weeks the ALS and the UEC will be working to develop the next edition of the ALS Highlights section of the annual Activity Report. In this we will try to include probably 20 to 30 research highlights from the last year in a small brochure that is fairly widely distributed. Please feel free to try to impact this process--we need your advice!

7. WHO'S IN TOWN: A SAMPLING OF ALS USERS

To highlight the richness of our user community and help introduce recent arrivals, we offer this listing of some of the experimenters who will be collecting data during the next two weeks at the ALS.

Beamline 1.4.3: Ron Simms, Karl Neiman (Utah State Univ.) and Hoi-Ying Holman (Berkeley Lab) will investigate pyrene degradation and bound residue formation in the presence of humic acids. James Chesko (Alza Corp.) will be studying semipermeable membranes. Kevin Wilson and Richard Saykally (Univ. of California, Berkeley) will be investigating the edges of water microjets. Felicia Hendrickson and Bob Glaeser (Berkeley Lab) will continue their investigations of the photocycle of bacteriorhodopsin microcrystals.

Beamline 7.3.1.1: Gary Mitchell (Dow Chemical) will study polymer interactions with the PEEM2 photoemission electron microscope.

Beamline 7.3.3: Roger Falcone's group (Univ. of California, Berkeley) will do time-resolved x-ray diffraction of Nd1/2Sr1/2 MnO3.

Beamline 8.0.1: Satish Myneni (Berkeley Lab) and Anders Nilsson (Univ. of Uppsala, Sweden) will be working on organic molecule protonation and metal complexation in aqueous solutions. Jan Luening, Joachim Stoehr (IBM Almaden), Stefan Eisebitt, and coworkers (Institut fuer Festkoerperforschung, Juelich, Germany) will be performing speckle spectroscopy of magnetic thin films.

Beamline 10.0.1: Scot Kellar, Z.X. Shen, X. Zhou, and P. Bogdanov (Stanford University) will continue their studies of highly correlated electronic systems using the HERS endstation. F. Wuilleumier, J.-M. Bizau, D. Cubaynes (LSAI, France), and coworkers will study multiply excited lithium atoms with high-resolution electron spectroscopy.

8. OPERATIONS UPDATE
(Contact: RMMiller@lbl.gov)

Beam reliability for the last two weeks (October 11 to 24) was 91.6% for user shifts. There were a number of outages last week related to components of the storage ring rf system (klystron anode tube replacement and klystron window blower and klystron ion pump trips). In addition, a power dip on Sunday, October 24, tripped many ALS systems. Frequent adjustments were required to both the longitudinal and transverse feedback systems during the week.

Long-term and weekly operations schedules are available on the Web (http://www-als.lbl.gov/als/accelinfo.html). Requests for special operations use of the "scrubbing" shift should be sent to Bob Miller (RMMiller@lbl.gov, x4738) by 1:00 p.m. Friday. The Accelerator Status Hotline at (510) 486-6766 (ext. 6766 from Lab phones) features a recorded message giving up-to-date information on the operational status of the accelerator.