Copyright 2010 by the American Chemical Society
VOLUME 114, NUMBER 3, JANUARY 28, 2010
Tribute to W. Carl Lineberger Pinning down the many research accomplishments and behind-the-scenes impact of Carl Lineberger is no easy task. Those who have worked with Carl, for example, know well to listen carefully when he modestly shares his “child-like view” regarding some aspect of science or strategy, as that is when you are most likely to gain the deepest insights into how things really work. Carl has an uncanny knack for unraveling the subtle principles that organize complex phenomena at all levels of endeavor. It is as if there are actually two independent, equally resourceful personalities at work, each of which being capable of solving incredibly delicate, impossibly difficult problems that go straight to the heart of the matter. We consider first his research persona, where his trajectory includes laying the foundation of an entire field of chemistry that exploits the unique properties of negative ions to determine chemical reaction dynamics, molecular structure, and thermochemistry. This aspect of his work includes determination of the electron affinities of the elements, data which today appear in virtually every freshman chemistry textbook. Carl’s singular research accomplishments derive from his unusual combination of expertise in chemistry and physics together with mastery of engineering, which enabled him to attack new classes of chemical problems with his signature blend of elegance and precision. His name is associated with every important paradigm in the field of negative ion spectroscopy.
These successes started in the early 1970s with the threshold laws and atomic physics of photodetachment. His two-pronged approach of using ultra high-resolution, mass-resolved electron photodetachment complemented by photoelectron spectroscopy has proven extraordinarily productive over the past forty years. It is essential to emphasize that Lineberger has contributed much more than experimental techniques. Once he develops a method, he immediately exploits it to broaden and deepen our understanding of chemistry. In one example, he demonstrated how to use photoelectron spectroscopy to generally measure singlet-triplet splittings in organic molecules. This followed an earlier study in which he extended photodetachment from excitation of continua to include the first high-resolution spectrum of a molecular anion (C2-). The latter study was quintessentially “Lineberger” in that he obtained the spectrum using a resonant two-photon (R2PI) scheme where the first photon excited the molecule to a bound electronically excited state and the second photon ejected the electron, which could be detected with great sensitivity. Five years later, this effect was rediscovered by physical chemists who fell head-over-heels for multiphoton ionization spectroscopy (MPI) of neutrals. He has also shown how to use electron affinities, in conjunction with other measurements to establish the sequential bond energies for the decomposition of simple organic molecules, one bond at a time, by all paths! Starting in the 1980s, he
10.1021/jp911601g 2010 American Chemical Society Published on Web 01/21/2010
1226
J. Phys. Chem. A, Vol. 114, No. 3, 2010
pioneered the application of ultrafast pump-probe methods to size-selected cluster beams to establish how a precisely controlled number of solvent molecules affects the photodissociation dynamics of a diatomic anion. Having started with the simple atomic anions so many years ago, these ongoing “cagerecombination” experiments reveal how solvent molecules control the dynamics of a chemical reaction. Very recent results in this aspect of his program have established that addition of as few as two solvent molecules (CO2) can facilitate IBrrecombination following excitation of the molecular ion to a nominally repulsive electronic state. A particularly impressive display of Carl’s combination of insight and technical virtuosity is his demonstration of how negative ion photoelectron spectroscopy can be used to directly measure the shape of the potential surface in the transition state region of an isomerization (vinylidene f acetylene) reaction. This experimental approach anticipated the revolution in wavepacket techniques to study reaction dynamics and was instrumental in paving the way for elegant determinations of transition state spectra for neutral bimolecular reaction encounters. Following his lead, researchers around the world now form a large community continuing to reap the rewards made available by applying Lineberger’s methods. We now turn to the second aspect of Carl’s impact: his pivotal role in maintaining physical science as a healthy and central component of the contemporary research portfolio. His unique style of understatement in the delivery of persuasive arguments has made his voice among the most influential at the highest levels, especially through his many projects at the National Academy of Sciences involving oversight of science policy and personnel. Carl has not shied away from contentious issues. On the contrary, he seems drawn to them because their resolution is key to progress when there are many conflicting opinions about how to best distribute limited resources. Carl’s legendary
work behind the scenes rivals his substantial contributions in basic science, and he is an inspiring role model on effective leadership while minimizing unnecessary conflict. Over the years, Carl Lineberger has been a constant source of wisdom and enthusiasm for research at the core of physical chemistry. His presence at a scientific meeting elevates its stature with his acute questions during formal symposia, but equally well in the corridors where much of the real information is exchanged. One of the aspects that we have particularly enjoyed is his ability to communicate what he thinks is “hot” and why. This, in part, explains his unchallenged leadership of the field. It is always refreshing to bounce a new idea off of Lineberger since you know his reaction will genuinely reflect his razor sharp intuition about how chemistry works. When you interact with Carl, you have the unmistakable feeling that you are dealing with someone who understands molecular physics at a profound level. He makes sense out of chaos, and that ability inspires confidence among his co-workers. The many and varied papers in this collection are testimony to Carl’s wide ranging interests and overall impact on our field. Together with an international group of colleagues and co-workers, we wish Carl Lineberger continued success, and offer our thanks for his gracious and effective leadership, for his pioneering research achievements, and for his insights on future directions that continue to shape our collective scientific adventure.
Mark A. Johnson Yale UniVersity Anne B. McCoy The Ohio State UniVersity JP911601G
