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Autobiography of Klaus Mu¨ller-Dethlefs How I got into science: At my school in Dortmund, I developed my keen interest in research - and won a national youngresearchers’ competition in North-Rhine Westphalia in Chemistry. As a result, I got a grant to go to university in Go¨ttingen to study Chemistry and Physics. It is fair to say that I achieved a family ambition: “My father was a technician, but the family couldn’t afford to send him to university. He was determined that I should go.” My training as a spectroscopist goes back to my undergraduate days at Go¨ttingen, where my Chemie Diplomarbeit, concerned with optical combustion diagnostics and spectroscopy, won me a First. “I was always curious. As a boy, I had a great interest in anything to do with mathematics and the nature of things. As an undergraduate, I developed a keen interest in laser spectroscopy and laser optical measurements with a view at that time to applying them to combustion systems.” Ph.D. and Postdoc: During my Ph.D. with Felix Weinberg at Imperial College, I developed a laser light scattering and fluorescence measurement technique to study soot formation in flames. As postdoc with J.-P. Taran at ONERA, with a grant from the Deutsche Forschungsgemeinschaft, I applied coherent anti-Stokes Raman spectroscopy (CARS) to the sensitive detection of H2 and C2 in flames. Starting my own research group: In 1980, I was given the chance by Edward W. Schlag to set up my own research group at the Technische Universita¨t Mu¨nchen, an institution at the forefront of molecular spectroscopy and dynamics. It was there in 1984 when I made the big ZEKE discovery. ZEKE spectroscopy: a half-day experiment? I started my own research group at the TU Mu¨nchen, and in summer 1984 I arrived at the principle of Zero Electron Kinetic Energy (ZEKE) photoelectron spectroscopy that suited me well: just photoionize and wait! An electron without kinetic energy, produced by threshold ionization, must have zero velocity and will hence just stay in the ionization region in contrast to a kinetic electron. In a half-day experiment that truly lived up to its name, my student Michael Sander and I obtained the 3+1′ rotationally resolved ZEKE spectrum of NO through the C intermediate state, showing the fully resolved rotational structure of the NO+ cation exactly as predicted! A new method of molecular ion spectroscopy was born, nearly 3 orders of magnitude better than conventional photoelectron spectroscopy! At a meeting in Tutzing close to Munich, Dick Zare, together with my former advisor in Go¨ttingen, Heinz-Georg Wagner, got really excited about this rotationally resolved ZEKE spectrum of NO and he immediately got me an invitation to give a lecture at the International Conference on Laser Spectroscopy, Mauii, Hawaii, 1985, with a stopover at ZareLab. Failure, despair, endurance and...finally success: Pulsed field ionization of long-liVed ZEKE Rydberg states! Then, with my students Georg Reiser, Wieland Habenicht, and Robert Baumann I constructed a completely new ZEKE apparatus aiming to further improve the previously obtained ZEKE resolution. However, by the end of 1987 the project was in a deep crisis; not only did we get no improvement but the resolution was worse! After The Gordon Conference on Multiphoton Processes in June 1988, we had a discussion at Yale hosted by Mark Johnson with Bill Chupka, Ed Eyler, and Steve Colson about the discrepancy between the ionization energy of
NO obtained from Rydberg extrapolation and ZEKE. Still, the issue was only resolved back in Garching, when the answer came finally from the conclusion that very high-n Rydberg states were contributing to the ZEKE signal. I realized that the electric field pulse in my new machine had too fast a rise time! With my own hands I made a box that produced a slowly rising pulse that was designed to separate free electrons from the electrons produced from sequentially pulsed field ionizing high-n Rydberg states. Using my new Le Croy 8828C transient digitizer connected to my newly acquired HP 20 MHz 386 PC (as suggested by Phil Johnson during my visit at Stony Brook), I could see that ZEKE signals arose from both continuum electrons and from the pulsed field ionization of long-lived Rydberg states. The riddle was solved! With the slowly rising pulse, the Rydberg states were sequentially ionized and I obtained perfect agreement between the ionization energy obtained from ZEKE and the Rydberg f-series extrapolation. The next years saw a very dynamic extension of rotationally resolved ZEKE spectroscopy of a variety of molecules, including VUV excitation (Tim Softley, Fre´de´ric Merkt, Helen Fielding, and Michael G. White). Most important was the development of the theory for rotationally resolved molecular photoionization by Vince McKoy and, for angular photoelectron resolution, by Dick Zare and Katharine Reid. It was Bill Chupka who made a most valuable contribution to resolve the strange ultralong lifetime issue associated with ZEKE-Rydberg states: the mixing of electron angular momentum l and ml by small electric fields leading to a lifetime enhancement of the Rydberg states by a factor of n2. Applications of ZEKE spectroscopy, including ZEKE photodetachment transition state spectroscopy (Dan Neumark) became more predominant and over the years my efforts switched more to molecular clusters. Some of the highlights of this most productive period in Garching are summarized in a Chemical ReViews article in 1994. The full elucidation of the Jahn-Teller effect in the benzene cation with Ed Grant was another highlight. Rudolf-Kaiser-Preis: In 1994, I was awarded the RudolfKaiser-Preis of the StifterVerband fu¨r die Deutsche Wissenschaft for the development of the ZEKE method and my contributions to nonlinear laser spectroscopy. Important Conferences and the Far East connection: The Gordon Research Conferences on Multiphoton Processes were always a most stimulating source of new ideas. ZEKE spectroscopy led to two conference series, the European Research Conference on Highy Excited States and the Gordon Research Conference on Photoions, Photoionization, and Photodetachment. ZEKE spectroscopy, Rydberg dynamics, and photodetachment also were featured strongly at the Faraday Discussion “Molecular Photoionization” held in York, April 2000. After my first wife Ulrike passed away after long illness in 1999, Masaaki Fujii invited me as Visiting Professor to the Institute of Molecular Sciences (IMS) in Okazaki, Japan. This led to a most important visit to China. The “Beijing International Conference on Photoelectron Spectroscopy: Molecules, Ions, and Clusters”, September 1999, chaired by John Dyke and Barry Peel and organized by the Chinese Academy of Sciences, holds highest significance for both my scientific and personal life, since there I met my wife-to-be, Helen XiaoYing Hu.
10.1021/jp1079857 2010 American Chemical Society Published on Web 10/21/2010
J. Phys. Chem. A, Vol. 114, No. 42, 2010 11029 The move to York: In 1995, I was appointed to the Chair of Physical Chemistry at York, United Kingdom, where I introduced state-of-the-art laser-based methods for spectroscopy and dynamics to the Department of Chemistry. In York, I was able to focus my research increasingly on the study of noncovalent interactions in molecular clusters by spectroscopic and time-resolved methods. Supported by my substantial EPSRC grants and with Caroline Dessent (Ph.D., Yale) as PDRA (now Royal Society University Research Fellow at York) and Martin Cockett (now Senior Lecturer at York), we published a good number of papers on a variety of molecular clusters. In particular, we developed the variant of ZEKE spectroscopy, Mass Analyzed Threshold Ionization (MATI) toward highest resolution, and used this method very successfully for the determination of dissociation energies with spectroscopic precision (this is still the only method available that is generally applicable and most precise). With help from Pavel Hobza (Prague) and his group, we applied ab initio methods for the understanding of noncovalent interactions in molecular clusters; the experimental and theoretical results from the first four years in York were summarized in two Chemical ReViews in 2000. Centre for Laser Spectroscopy at York established from 2000 onward. Herzberg Memorial Prize: In recognition of my development of ZEKE spectroscopy, I became the first Herzberg Memorial Laureate and Fellow of the National Research Council of Canada in February 2001. The University of Manchester Photon Science Institute (PSI): The new Alan Turing Building provides outstanding laboratory, core laser, and instrumentation facilities. Scientists
from Schools of all four Faculties are actively engaged in establishing this unique interdisciplinary research center as a world-leading institute. In Manchester, I have been facing a new hugely exciting challenge, helping to bring this University to the international pre-eminence it deserves. “It is inspiring to know that photon science will light the way for future international research across so many scientific disciplines.” Today one field of my research is driven by the desire to better understand molecular clusters - it is fascinating to investigate how everything from macroscopic entities like liquids and biomolecular structures such as proteins and DNA are held together by noncovalent interactions. My book with Pavel Hobza “Non-coValent Interactions: Theory and Experiment”, published by the Royal Society of Chemistry in December 2009, summarizes what is presently known about molecular clusters. During the past few years I have developed a fascinating new experiment to produce an ultracold molecular plasma, which shows some interesting behavior. Twenty-five years of ZEKE spectroscopy: The symposium 25 Years of ZEKE Spectroscopy (organizers Dan Neumark, UC Berkeley, and Masaaki Fujii, Yokohama) at the ACS Annual Meeting, August 16-20, 2009, Washington, DC, forms the core of the present Festschrift and with greatest pleasure I would like to express my most sincere thanks and my appreciation to the guest editors Dan Neumark and Masaaki Fujii as well as the Editor of the Journal of Physical Chemistry A Michael Duncan and the staff of the editorial office.
Klaus Mu¨ller-Dethlefs JP1079857
