J. Phys. Chem. A 2010, 114, 11027
11027
Photo by Paul Cliff
Tribute to Klaus Mu¨ller-Dethlefs Anyone who has measured a photoelectron spectrum during the course of his or her scientific career will appreciate the power and generality of this technique, which, after all, has its roots in the photoelectric effect explained by Einstein in 1905. However, this appreciation is often tempered by a certain degree of exasperation at the relatively low resolution of photoelectron spectroscopy, which is typically 5-10 meV at best, in comparison to the much higher spectral resolution offered by purely optical methods. The development of Zero Electron Kinetic Energy (ZEKE) spectroscopy by Klaus Mu¨ller-Dethlefs in the 1980s essentially solved this problem. In ZEKE spectroscopy, neutrals are photoionized using a tunable laser, and, by means of an elegant electron optical design, only those photoelectrons produced by transitions to ion states very close to the laser frequency are detected. Klaus’s first paper on ZEKE spectroscopy showed a fully rotationally resolved spectrum of NO+ obtained via two-photon ionization of NO. Since then, ZEKE spectroscopy has been applied to many species, including biomolecules, metal and van der Waals clusters, and negative ions. It routinely yields sub-meV resolution and often does considerably better than that. Moreover, efforts to understand the underlying ionization mechanisms in ZEKE have led to new conceptual frameworks for describing highly excited Rydberg states in atoms, molecules, and clusters. This knowledge has seeded the development of variations on ZEKE such as Mass-Analyzed Threshold Ionization, which combines the energy resolution of ZEKE with the detection of mass-selected ions rather than electrons. ZEKE has been incorporated into time-resolved experiments by one of us (M.F.), while an other (D.N.) has adapted ideas from ZEKE into a high-resolution negative ion photodetachment technique based on slow photoelectron imaging. Overall, the impact of ZEKE spectroscopy on the field of molecular photoionization has been
vast. This special issue is a celebration of experimental and theoretical aspects of ZEKE spectroscopy, experiments that have been motivated by ZEKE, and, more importantly, Klaus Mu¨llerDethlefs. Klaus is currently Professor of Chemistry and Physics at the University of Manchester. He was the first Director of the Photon Science Institute at Manchester. He was awarded the Rudolf Kaiser Preis in Experimentalphysik in 1994 and in 2000 was the first Herzberg Memorial Prize Laureate of the National Research Council of Canada. Over the years, Klaus’s friends and colleagues have come to know and admire his unique combination of superb scientific insight and enthusiasm for life outside the laboratory. Klaus is still trying to master certain aspects of the latter; it is much safer to be with him in a bar than on a golf course, for example. But perhaps the most impressive demonstration of Klaus’s ability to combine scientific and extracurricular activity was at the 1999 conference on photoelectron spectroscopy in Beijing, where Klaus not only gave a superb talk but also ended up marrying the conference liaison and having two beautiful boys by her. Klaus, on this occasion of your 60th birthday, we salute your accomplishments and wish you many more years of continued scientific excellence.
10.1021/jp106204d 2010 American Chemical Society Published on Web 10/21/2010
Daniel Neumark UniVersity of California Masaaki Fujii Tokyo Institute of Technology Michael Duncan UniVersity of Georgia JP106204D
