2008
Tuesday, April 15th and Thursday, April 17th
Professor Carl Lineberger

4:15 - 5:15 pm	4:15 - 5:15 pm
Tuesday, April 15th	Thursday, April 17th
Braun Lecture Hall	Clark Center Auditorium

This seminar is free and open to the public. All Stanford University Chemistry students are encouraged to attend this special event.

Abour the Seminars:

Tuesday, April 15th
Ultrafast pump-probe studies of recombination in partially solvated, size-selected dihalide cluster anions show long time coherent motions and the resulting non-statistical energy flow in the cluster. For photodissociated I2?(CO2)n, we observe new type of recombination: a solvent asymmetry-driven energy transfer process without a condensed phase counterpart. Very short recombination times are observed (~10 ps) with the chromophore only partially solvated, and the time required for recombination steadily decreases with additional solvation. This process can be described in terms completely analogous to the Marcus description of electron transfer in condensed phase. The model also points to the central role of the solvent electric field in the recombination process, but suggests an important role of electron transfer processes that cannot be tested with a homonuclear dihalide chromophore. To further test these concepts, we investigate the time-resolved recombination of photodissociated IBr-(CO2)n clusters following excitation to the dissociative IBr- A? 2?½ state of the chromophore. When partially solvated, the solvent is quite localized about the smaller bromide end of the chromophore, as seen in the structure of IBr?(CO2)8.



In complete contrast to previous studies involving solvated I2-, the observed recombination times for IBr-(CO2)n increase dramatically with increasing cluster size, from 12 ps for n=5 to 900 ps for n= 8,10. The nanosecond recombination times are especially surprising in that the overall recombination probability for these cluster ions is unity. For larger cluster sizes, the recombination time returns to the expected ps time. This very unexpected behavior provides an even more exacting test of the theoretical model. Comparisons between theory and experiment confirm the presence of a solvent-induced excited state trap that is present only over a small range of solvent sizes. The comparisons demonstrate directly the utility of the solvent electric field as a “solvent coordinate” to describe the caging process.


"Photoelectron Spectroscopy of Organic Anions: Radicals, Reactive Intermediates and Transition States" Thursday, April 17th
Over the past 30 years, anion photoelectron spectroscopy has been an especially fertile arena for fruitful interactions between experimental measurements and quantitative theoretical determinations of the structure and thermochemistry of small molecules, radicals and reactive intermediates. In this lecture, I briefly review some of these past studies, and focus on current projects where the interplay between theory and experiment is especially productive. The areas of emphasis will include spin states of carbenes, electron affinities, bond strengths of radicals, direct observation of transition states..

About the Johns Stauffer Lecturer Series:
In 1993, the Department of Chemistry received a generous gift from the Stauffer Foundation to endow an annual series of lectures. The Stauffer Lectures have been very successful and are always widely attended. Previous presenters have included Professors Richard Smalley, Gregory Petsko, Jean-Marie Luhn, Jeremy Berg, George Whitesides, Ahmed Zewail, Jean Fréchet, Alan Fersht, Harry B. Gary, Robert Silbey and Roger Tsien.

About Lineberger:
Carl Lineberger was born in Hamlet, North Carolina. He received his B.S. and Ph.D. degrees in Electrical Engineering from the Georgia Institute of Technology in 1965, working with John Hooper and Earl McDaniel in atomic collision physics. In 1968, he began postdoctoral work with Lewis M. Branscomb at JILA in Boulder. Subsequently, he joined the faculty of the Department of Chemistry and Biochemistry at the University of Colorado, and is now the E.U. Condon Distinguished Professor of Chemistry and Biochemistry and Fellow of JILA. His work is primarily experimental, using a wide variety of laser based techniques to study structure and reactivity of gas phase ions. These studies have provided many precise thermochemical properties of important ions, radicals and diradicals. Recent studies have been directed toward elucidating the structure of transient reaction intermediates, to developing understanding of the gradual evolution of physical properties from an isolated molecule to a solvated species and to real-time investigations of reaction dynamics including the cage effect in size-selected clusters. Specifically, he has employed ultrafast laser technology to elucidate the role of the solvent in the molecular cage effect in such clusters. He has published over 240 papers in major scientific journals, and his graduate students and postdoctoral associates hold major research-related positions throughout the world.

Carl has been awarded the H. P. Broida Prize in Atomic and Molecular Spectroscopy and the Earle K. Plyler Prize by the American Physical Society, the Meggers Prize by the Optical Society of America and the Michelson Prize by the Coblentz Society. He has received the Irving Langmuir Prize in Chemical Physics and the Peter Debye Prize in Physical Chemistry from the American Chemical Society. He is a member of the National Academy of Sciences (1983), the American Academy of Arts and Sciences (1995), a Fellow of the American Physical Society and the American Association for the Advancement of Science, as well as a member of Sigma Xi and the American Chemical Society.

Carl is involved in a number of science advisory activities. He has recently served on the Council of the National Academy of Sciences, the Governing Board of the National Research Council, and Chair of the National Science Foundation Advisory Committee for Mathematical and Physical Sciences. He is currently a member of the National Research Council Committee on Science, Engineering and Public Policy, the Council of the American Association for the Advancement of science, and is involved with several NSF-related advisory activities.


Questions
Please contact Patricia Dwyer at 650-723-4770.