Ahmed H. Zewail (1946-2016).

A hmed H. Zewail, an Egyptian-American scientist who won the 1999 Nobel Prize in Chemistry for pioneering investigations of fundamental chemical reactions on the femtosecond time scale, died on 2 August 2016. He was 70 years old. Zewail was an academic star at the California Institute of Technology (Caltech) and spent his final years advocating for investment in science education and research in Egypt. Zewail was born in 1946 in Damanhur, Egypt, and studied at Alexandria University in the city where he grew up. After earning bachelor’s and master’s degrees, he looked abroad to pursue his Ph.D. in chemistry. Egyptians seeking overseas education in 1969 typically went to the Soviet Union. In a stroke of good fortune, the University of Pennsylvania offered him a scholarship and he came to the United States. After earning his doctorate from Penn, he spent 2 years as a postdoctoral researcher at the University of California, Berkeley, and then joined the faculty at Caltech in Pasadena in 1976. Zewail, the Linus Pauling Professor of Chemistry and professor of physics, set out to make movies of chemical reactions with the world’s fastest camera—one with shutter speed measured in femtoseconds, a millionth of a billionth of a second. Before Zewail’s work, chemists could only infer the structures of short-lived intermediates between reactants and products during the breaking and making of bonds in chemical reactions. Transition states are so fleeting that they had never been observed directly. A femtosecond is shorter than the period of a nuclear vibration or rotation in the molecule and Zewail was able to freeze the system in time using ultrafast laser spectroscopy. Zewail’s brilliant insight was the demonstration that rotational and vibrational coherence is the key to making femtosecond movies. He was able to choreograph an ensemble of molecules and synchronize their motion. Using two laser pulses—a pump pulse to start the clock and trigger the reaction, followed by a probe pulse—Zewail photographed snapshots of the evolution of chemical reactions. Zewail’s hero and friend, Caltech’s Linus Pauling, won the Nobel Prize in 1954 for his research on the nature of the chemical bond. Zewail connected the chemical bond to its dynamics by setting those bonds in motion. Zewail received honors from around the globe, including 46 honorary degrees, the Grand Collar of the Order of the Nile (Egypt’s highest state honor), and the Order of Légion d’Honneur. He was an elected member of academies and learned societies including the U.S. National Academy of Sciences, the Royal Society of London, the American Philosophical Society, the French