1. DYNAMICS OF PENTANE AND PROPANE METATHESIS REACTIONS
by Art Robinson
Contact: AGSuits@lbl.gov

Crossed-molecular-beam scattering is at the forefront of experimental means of investigating the fundamental reactive encounters in metathesis reactions, in which a single atom is transferred from a stable molecule to an atom or radical. Berkeley Lab researchers are exploiting a unique combination of intense, tunable VUV synchrotron radiation with the crossed-beam technique on Beamline 9.0.2 at the ALS to yield important new insights into the dynamics of hydrogen transfer (abstraction) when chlorine reacts with the saturated hydrocarbons pentane and propane.

Metathesis reactions are the only truly bimolecular (i.e., bimolecular in both directions) gas-phase reactions. Those reactions involving hydrogen atom transfer arguably represent the most important subclass of the vast body of reactions. Free-radical abstractions of hydrogen atoms in saturated hydrocarbons, for example, are reactions of great importance in combustion, and the differing propensities for reaction of primary, secondary, and tertiary hydrogen atoms, as well as the different dynamics underlying these pathways, are central to a detailed understanding of combustion chemistry.

The researchers at the ALS have measured global scattering distributions for reaction of chlorine atoms with saturated hydrocarbons. These measurements provide extremely detailed information about these reactions, providing answers to questions such as, What are the initial products of the reaction? Where does the energy of the reaction go? Are the products cold (energy mainly in translational motion) or hot (energy mainly in vibrations) or some of each? The use of tunable undulator radiation provides the unprecedented ability to probe the reactive hydrocarbon radical fragment directly in these reactions. Initial studies of the reaction of chlorine with propane suggested different dynamics for the forward- and backward-scattered products. The researchers have now extended these studies to the reaction of chlorine with n-pentane, Cl + n-C5H12 --> HCl + C5H11, to examine the underlying trends in the dynamics with an eye to the role of the extended carbon skeleton in these reactions.

The experimental results show that the forward-scattered products are clearly associated with the formation of the lowest-energy 2-pentyl radicals, while the backscattered products arise from close collisions preferentially involving the terminal carbons to produce 1-pentyl radicals. The forward-scattered products are formed extremely cold and with velocities largely beyond the limit accessible to the 1-pentyl radicals. For the backscattered products, however, virtually all of the energy of the collision is deposited into the 2-pentyl radicals, producing extremely hot, reactive products. This is very different from what was observed in other related systems. In fact, previous studies relying on state-resolved laser probing of the HCl have often assumed that no energy is deposited into vibration of the radical product. The ALS results clearly show that this is incorrect.

Moreover, a dramatic difference observed in the dynamics of the backscattered channel for pentane as compared to propane, the researchers believe, arises from the presence of the extended carbon chain and the larger density of states for the pentane reaction. Estimates show that the 20-femtosecond time scale of the collision is very close to a half-period of the bending vibrations of the carbon backbone, making energy transfer from the collision to the C-C-C bends very efficient. These insights will help build the foundation for developing accurate computer models of practical combustion systems.

Research conducted by D.A. Blank, N. Hemmi, and A. G. Suits (Berkeley Lab) and Y. T. Lee (Academia Sinica, Taiwan).

Funding: U. S. Department of Energy, Office of Basic Energy Sciences.

Publications about this experiment: D. A. Blank, N. Hemmi, A. G. Suits, and Y. T. Lee, Chem. Phys. 231, 261 (1998); N. Hemmi and A. G. Suits, J. Chem. Phys. 109(13), 5338 (1998).

2. ALS USERS' MEETING SET FOR OCTOBER 18-20, 1999
Contact: alsuser@lbl.gov

It's never too early to plan ahead, so take the time and mark your calendar for this year's ALS Users' Meeting, to be held from Monday, October 18, to Wednesday, October 20. The meeting will take place at Berkeley Lab and will showcase recent scientific achievements at the ALS. The work of students and young researchers will again be highlighted in both oral and poster presentations. A call for abstracts will be sent out to ALS users, staff, and students in early summer. Keep an eye on the ALS Users' Executive Committee Web page at http://www-als.lbl.gov/als/uec/index.html for future updates. And while you are marking your calendar, don't forget to start thinking about an entry for this year's Users' Meeting T-Shirt Design Contest!

3. NEW INTRANET GIVES STAFF ACCESS TO ALS-RELATED INFORMATION
Contact: annette_greiner@lbl.gov

A new system is now available for sharing facility-related information among ALS staff: the ALS Intranet. This Web-based system is only accessible to staff on site at Berkeley Lab. It will provide information that is valuable to those who work at the ALS but is not of interest to the general public. The information currently available includes ALS procedures, ALS nomenclature and CAD drawings, and administrative information related to purchasing. It is accessible now via any Web browser on the hill. Just point your browser to http://alsintra.lbl.gov/. The ALS Intranet can also be reached through the ALS Internet Web site. Follow the "ALS Intranet" text link near the bottom of the ALS home page (http://www-als.lbl.gov).

We expect the intranet content to change and grow over time to meet the needs of those who use it. In order to make the system as useful as possible, we ask that staff members consider what information might be useful to them and other people who work at the ALS and let us know your ideas. In making suggestions, please bear in mind that this is not a world-wide system, so any material meant for access outside the lab will not be appropriate. Send your suggestions to Annette Greiner (annette_greiner@lbl.gov, ext. 6711).

4. ADMINISTRATIVE SUPPORT CHANGES
Contact: NATalcott@lbl.gov

Several changes in administrative staffing will occur in the coming weeks. Joan Minton has accepted a new assignment within Berkeley Lab's Administrative Services Department. She will move in the next week or so to the Physical Biosciences Division, to work with Division Director Graham Fleming and Kristin Balder-Froid, Program Development Administrator. Among other assignments, Joan will be involved in coordinating and developing research and grant proposals for the division. While the search for Joan's replacement is conducted, Jennifer Slatten will assist Ben Feinberg and Neville Smith and perform special projects for the ALS division office. Jennifer is an Administrative Assistant III who has experience working in several divisions at the Lab over a number of years. She will transition with Joan beginning early this week. All of us at ALSNews wish Joan the best in her new assignment. She will be sorely missed.

In other administrative news, Barbara Phillips will move to the ALS User Services Office under Ruth Pepe. Her duties will expand to providing administrative and logistical support for the ALS apartments. She will also take on other assignments within the ALS User Services administrative team.

5. POSTDOCTORAL OPPORTUNITY
Contact: lindle@nevada.edu

A full-time postdoctoral position in synchrotron radiation research, focusing on gas-phase and materials studies at the ALS, is available through the University of Nevada, Las Vegas. For more information, see the posting at http://www.nscee.edu/XAMS/job.html.

6. 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 1.4.1: Joel Ager and Wei Shan (Berkeley Lab) and Eugene Haller (Univ. of California, Berkeley) will continue their UV photoluminescence studies of GaN compounds.

Beamline 1.4.3: Felicia Hendrickson and Bob Glaeser (Univ. of California, Berkeley) will continue infrared spectroscopy of protein microcrystal conformation changes.

Beamline 7.0.1: Marjorie Olmstead (University of Washington at Seattle) will conduct photoemission studies of III-VI materials, Z.Q. Qiu (Univ. of California, Berkeley) will perform photoemission studies of quantum confinement in metallic thin films, Joseph Nordgren (Uppsala University) will study soft x-ray fluorescence of materials and molecules, and Dave Shuh (Berkeley Lab) will use soft x-ray emission spectroscopy to investigate environmental materials.

Beamline 7.3.1.1: Boris Sinkovic and Laurent Seve (University of Connecticut) will study nanofabricated magnetic structures. Jan Luening and Jan Thiele (IBM) will study magnetic multilayer structures and magnetic hard disk materials.

Beamline 8.0.1: Dennis Lindle (Univ. of Nevada, Las Vegas) will probe the limits of fundamental approximations in x-ray photoelectron spectroscopy, and Jonathan Denlinger (University of Michigan) will conduct photoemission studies.

Beamline 9.3.2: Eric Kneedler (Univ. of Wisconsin-Milwaukee) and Brian Tonner (Univ. of Central Florida) will conduct a photoelectron diffraction study of clean and chemically modified mineralogical surfaces.

Beamline 10.3.1: Dale Sayers (North Carolina State Univ.) and Pavel Pleshanov (The Ecological Institute, Moscow) will be studying trace element contamination in lung lavage residue. The lung lavage samples come from people who lived or worked in Cherynobyl.

7. OPERATIONS UPDATE
(Contact: rmmiller@lbl.gov)

Beam reliability for the last four weeks (December 21 to January 17) was 89% overall and 93% for user shifts. The largest interruption was due to the failure and repair of the high-power trigger circuit for storage-ring bump magnets.

Long-term and weekly operations schedules are available on the Web (http://www-als.lbl.gov/als/accelinfo.html). Weekly operations scheduling meetings are held on Fridays at 3:30 p.m. in the Building 6 conference room. 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.