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Stanford Report, February 2, 2000

Clinton awards Medal of Science to John Ross


President Bill Clinton on Monday named Stanford chemistry Professor John Ross as one of 12 pioneering researchers who will receive the 1999 National Medal of Science. Established by Congress in 1959, the medal is the nation's highest scientific honor. The awardees will receive their medals March 14 at a White House ceremony along with the five recipients of the National Medal of Technology.

Ross, who is the Camille and Henry Dreyfus Professor of Chemistry at Stanford, is honored for his enormous impact in physical chemistry, especially in molecular studies, statistical mechanics and the chemical kinetics of nonlinear systems, and for opening up new fields in chemical science.

"Ross is one of the most original and profound thinkers in the world in chemical science," said John Brauman, the J. G. Jackson -- C. J. Wood Professor of Chemistry at Stanford. "He has continually made major theoretical and experimental contributions in reaction kinetics and dynamics that have changed the way we think about chemical reactivity and allowed us to understand why many chemical phenomena occur."

Counting today's recipients, 374 American scientists and engineers have received medals since President John F. Kennedy made the first award in 1962. Ross is the 38th chemist and 26th Stanford scientist to receive the honor.

"John Ross is a giant in the area of physical chemistry, having made pioneering theoretical and experimental studies in chemical kinetics, which is the study of how fast and by what means chemical transformations take place," said Richard Zare, the Marguerite Blake Wilbur Professor in Natural Science at Stanford.

Raymond Kapral, professor of theoretical chemical physics at the University of Toronto, said that "for the past 10 or 15 years Ross has been tackling the long-standing and difficult problem in chemistry of how to unravel the mechanisms of complex chemical reactions. The problem is especially nasty for biochemical processes that are responsible for how living systems behave. The problem is hard because the reactions are complicated, taking place far from chemical equilibrium and involving many chemical species."

For more than a century, scientists studying complex systems have identified chemical species and then isolated single reactions involving those species. "They tried to figure out how it all fits together, and this was done by experience, intuition, guesswork," says Ross, who takes a unique approach to studying complex systems. "I think we've broken that barrier."

The traditional approach, Ross says, is analogous to a person listening to music on the radio, wanting to understand how the radio works, smashing it with a sledgehammer to reveal its parts, then saying, "Ah, yes. This is a transistor. This is a wire. This is a battery. I understand how it works."

Instead of smashing the radio, Ross has pioneered new approaches to analyzing how complex chemical systems are linked. He suggests it is better to study intact systems -- that is, study functions not by smashing the whole system but by applying inputs and measuring outputs and correlating them. The analytical tools he devised help scientists determine what chemical species are most important in a complicated reaction mechanism and how they are linked through specific types of chemical reactions.

"Let's keep the chemical system all together, analyze as many chemicals as possible, include variable inputs, and measure responses of species," Ross says. "From that we construct a theory based on correlation functions. We look at each correlation function like sticks of different length. When the correlation is high, the stick is short, as the distance between reactants is small when reactants are strongly correlated. When the correlation is low, the stick is long, as the distance between reactants is great when reactants are weakly correlated. Then we tell the computer, 'Please build me an object with these sticks using multiple dimensional scaling analysis to show how the chemical species are connected in the system.' It's a way to determine reaction pathways and mechanisms, not by guessing but from experiments."

"I expect that this approach will have far-reaching and lasting consequences on the study of complex reaction systems," Zare says. "Ross's work is most definitely changing the way we think about and understand chemical reactivity."

Ross's work on complex reaction systems derived from his earlier studies on the implementation of computational functions. His chemical "computer" performs computations involving chemical kinetics on macroscopic scales -- that is, scales involving gram or mole quantities rather than molecules. To do this, he first makes a "logic gate" -- for example, "IF AND ONLY IF chemical species 1 and 2 are high in concentration, THEN AND ONLY THEN is the concentration of species 3 high." Using such gates, Ross and his students in 1991 designed the chemical analog of a universal Turing machine, which can perform all general computations.

In 1995, Ross and coworkers designed a chemical "parallel computer," which executes many computations simultaneously. With it, they performed the first pattern-recognition experiments using chemical reactions rather than electronics.

The path to success

Born in Vienna on Oct. 2, 1926, Ross left Austria due to religious persecution a few days before the outbreak of World War II and settled in New York with his parents. He majored in chemistry at Queens College, interrupting his education to serve in the Army from 1944 to 1946. After graduating in 1948, he entered the Massachusetts Institute of Technology, where he studied gas transport properties under physical chemist Isador Amdur and earned a Ph.D. in 1950. Subsequently he worked on gas thermometry, and on the statistical mechanical theory of irreversible processes with physical chemist John G. Kirkwood at Yale. These mentors helped form his standards of scholarship and appreciation for a balance of theory and experiment in science.

Ross was appointed an assistant professor in chemistry at Brown University in 1953 and started a program to test the viscosity of liquids as a function of temperature and pressure. His measurements -- the first at elevated pressures and temperatures below 0 degrees Celsius -- have never been surpassed in precision and accuracy.

In 1955, he and the physical chemist Edward F. Greene began pioneering research in the field of molecular beams that lasted until 1973. Beams reveal such molecular details of chemical reactions as whether molecules hang around or disperse after a collision, at what angles they disperse, and what types of complex interactions result if they do not disperse.

Ross was chair of the Chemistry Department at MIT from 1966 to 1971 and faculty chair at that institution from 1975 to 1977. He was the Frederick G. Keyes Professor at MIT (1971-1979). In 1979 he moved to Stanford, where he chaired the Chemistry Department from 1983 to 1989. He also has chaired the Division of Physical Chemistry of the American Chemical Society and the Division of Chemical Physics of the American Physical Society.

Ross has served as an adviser to government and industry and holds three patents. He has been on the Board of Governors of the Weizmann Institute of Science since 1972 and is a member of the National Academy of Sciences and the American Academy of Arts and Sciences. He has received NSF, Sloan and Guggenheim fellowships, the Irving Langmuir Award of the American Chemical Society, honorary degrees from Queens College, the Weizmann Institute and the University of Bordeaux, and a medal from the Collège de France.

With Steve Berry and Stuart Rice, Ross is coauthor of Physical Chemistry, an authoritative reference work. The author of 375 published studies, Ross even has been the topic of one publication. The Journal of Physical Chemistry published a festschrift in honor of his 70th birthday on Dec. 5, 1996. (German for "festival writings," a festschrift is a volume of learned writings and essays contributed by colleagues and admirers as tribute to a scholar.)

In 1992 Stanford honored Ross with the Dean's Award for Distinguished Teaching. In the past 50 years, he has mentored more than 160 doctoral candidates and postdoctoral researchers. "They have contributed enormously, and I am proud of them as my finest product," he says. "The medal is a wonderful reward for all the work my students and I have done through all these years." SR