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440:, a field of fundamental importance for all of molecular- and nano-science. Before Klemperer introduced spectroscopy with supersonic beams, the spectra of weakly bound species were almost unknown, having been restricted to dimers of a few very light systems. Scattering measurements provided precise intermolecular potentials for atom–atom systems, but provided at best only limited information on the anisotropy of atom–molecule potentials.
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463:. The observed microwave transitions all involved a simultaneous change in rotational and tunneling energy. The tunneling frequency is extremely sensitive to the height and shape of the inter-conversion barrier, and thus samples the potential in the classically forbidden regions. Resolved tunneling splittings proved to be common in the spectra of weakly bound molecular dimers.
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extremely stable molecule and thus its isoelectronic analog, HCO, whose structure and spectra could be well predicted by analogy, would also be stable, linear, and have a strong but sparse spectrum. Further, the chemical models he was developing predicted that HCO would be one of the most abundant molecular species. Laboratory spectra of HCO (taken later by Claude Woods
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the questions that could be asked. Nowadays it is routine for microwave and infrared spectroscopists to follow his "two step synthesis" to obtain the spectrum of a weakly bound complex: "Buy the components and expand." Klemperer quite literally changed the study of the intermolecular forces between molecules from a qualitative to a quantitative science.
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was the first hydrogen bonded complex to be studied by these new techniques, and it was a puzzle. Instead of the simple rigid-rotor spectrum, which would have produced a 1 to 0 transition at 12 GHz, the lowest frequency transition was observed at 19 GHz. Arguing by analogy to the well known
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He foresaw that he could synthesize dimers of almost any pair of molecules he could dilute in his beam and study their minimum energy structure in exquisite detail by rotational spectroscopy. This was later extended to other spectral regions by
Klemperer and many others, and has qualitatively changed
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Klemperer's early work concentrated on the infrared spectroscopy of small molecules that are only stable in the gas phase at high temperatures. Among these are the alkali halides, for many of which he obtained the first vibrational spectra. The work provided basic structural data for many oxides and
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Klemperer helped to found the field of interstellar chemistry. In interstellar space, densities and temperatures are extremely low, and all chemical reactions must be exothermic, with no activation barriers. The chemistry is driven by ion-molecule reactions, and
Klemperer's modeling of those that
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Klemperer arrived at this prediction by taking the data seriously. The radio telescope data showed an isolated transition with no hyperfine splitting; thus there were no nuclei in the carrier of the signal with spin of one or greater nor was it a free radical with a magnetic moment. HCN is an
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occur in molecular clouds has led to a remarkably detailed understanding of their rich highly non-equilibrium chemistry. Klemperer assigned HCO as the carrier of the mysterious but universal "X-ogen" radio-astronomical line at 89.6 GHz, which had been reported by D. Buhl and L.E. Snyder.
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fluorides, and gave insight into the details of the bonding. It also led
Klemperer to recognize the potential of molecular beams in spectroscopy, and in particular the use of the electric resonance technique to address fundamental problems in structural chemistry.
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Bill
Klemperer was born in New York City in 1927 as the child of two physicians. He and his younger brother were raised in New York and New Rochelle. He graduated from New Rochelle High School in 1944 and then enlisted in the
291:, a position which was considered unlikely to lead to a faculty position, he was appointed full professor in 1965. He has remained associated with Harvard Chemistry throughout a long career. He spent 1968-69 on sabbatical at
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Klemperer introduced the technique of supersonic cooling as a spectroscopic tool, which has increased the intensity of molecular beams and also simplified the spectra.
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tunneling-inversion spectrum of ammonia, Klemperer recognized that the key to understanding the spectrum was to recognize that HF–HF was undergoing
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After one semester as an instructor at
Berkeley, Bill returned to Harvard in July 1954. Though his initial appointment was as an instructor of
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T.R. Dyke, B.J. Howard and W. Klemperer (1972). "Radio
Frequency and Microwave Spectrum of the Hydrogen Fluoride Dimer: A Nonrigid Molecule",
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Each rotational level was split into two tunneling states, with an energy separation equal to the tunneling rate divided by the
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E. Herbst and W. Klemperer (1973). "The
Formation and Depletion of Molecules in Dense Interstellar Clouds",
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The Bomem-Michelson Award for the advancement of the field of vibrational spectroscopy. awarded by the
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S.E. Novick, P.B. Davies, T.R. Dyke and W. Klemperer (1973). "Polarity of van der Waals
Molecules",
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in 1950, majoring in
Chemistry, and obtained a Ph.D. in Physical Chemistry under the direction of
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Inaugural George C. Pimentel
Memorial Lecturer, Chemistry Department, UC Berkeley. 1991-2.
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The Distinguished Service Medal, awarded by the U.S. National Science Foundation, 1981
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and 1979-81 as Assistant Director for Mathematical and Physical Sciences at the U.S.
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Video of Klemperer's Faraday Medal Lecture on the Chemistry of Interstellar Space
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that predicted an abundance of the molecular HCO ion that was later confirmed by
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methods into chemical physics research, greatly increasing the understanding of
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D. Buhl and L.E. Snyder (1970). "Unidentified Interstellar Microwave Line",
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W. Klemperer (1970). "Carrier of the Interstellar 89.190 GHz Line",
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in Physical Chemistry, awarded by the American Chemical Society, 1994
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727:, and P.G. Szanto (1975). "Laboratory Microwave Spectrum of HCO",
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The greatest impact of Klemperer's work has been in the study of
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from the Maryland Section of the American Chemical Society, 1992
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to FH–FH, interchanging the roles of proton donor and acceptor.
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Bill Klemperer has had many awards and honors, which include:
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W. Klemperer (1995). "Some Spectroscopic Reminiscences" ,
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Members of the United States National Academy of Sciences
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between atoms and molecules through development of the
149:(October 6, 1927 – November 5, 2017) was an American
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864:United States Navy personnel of World War II
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554:The Faraday Medal and Lectureship from the
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568:Honorary Citizen of Toulouse, France, 2000
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824:University of California, Berkeley alumni
405:Learn how and when to remove this message
251:Learn how and when to remove this message
859:Fellows of the American Physical Society
661:Journal of the American Chemical Society
574:from the American Chemical Society, 2001
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477:Fellow of the American Physical Society
854:Scientists from New Rochelle, New York
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607:chemistry.harvard.edu
563:University of Chicago
507:Irving Langmuir Award
438:intermolecular forces
339:improve this article
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289:analytical chemistry
225:improve this section
147:William A. Klemperer
18:William A. Klemperer
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579:References
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784:Brief Bio
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93:(A.B.),
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311:Science
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97:(Ph.D.)
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693:Nature
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