Thursday, August 22, 2013

Joel Bowman's view from the top of theoretical chemistry

"Imagine how sensational it would be if we could predict where and when a cloud will form," says Joel Bowman. Photo by Bryan Meltz, Emory Photo/Video.

By Carol Clark

As Joel Bowman flew across the country recently, on his way to collect the Herschbach Prize for theoretical chemistry, his attention turned to the clouds outside the jet’s window. What’s happening at the molecular level, he wondered, in a cloud at 30,000 feet?

“As we all know, clouds are essentially water in the gaseous state,” says Bowman, Samuel Candler Dobbs Professor of Theoretical Chemistry at Emory. “And, of course, it’s really cold at that altitude. So why do you find clouds at sub-zero temperatures? It’s an obvious but interesting question. The answer certainly has something to do with energy the cloud has absorbed from the sun and with potential energy surfaces: The delicate, attractive forces holding little water molecules together.”

Bowman’s work on developing potential energy surfaces is just one example of why he received the Herschbach Prize for Theory, presented in July at the Dynamics of Molecular Collisions 2013 Conference. The prize is named for Nobel Prize winning chemist Dudley Herschbach, who describes the award’s criteria as “bold and architectural work” that “addresses fundamental, challenging, frontier questions … and typically excites evangelical fervor that recruits many followers.”

The two-sided medal for the Herschbach Prize represents both theoretical (left) and experimental (right) molecular collision dynamics. The designer chose an angel for theory to symbolize “our yearning to attain an exalted, exhilarating comprehension."

Bowman was also recently elected to the International Academy of Quantum Molecular Sciences, and is lauded in the August 15 issue of the Journal of Physical Chemistry, the leading journal in its field. The cover art shows results from two of Bowman’s recent collaborations with experimentalists: One, concerning the dynamics of clusters of water molecules and another involving the complex kinetics of the chemicals in a comet. This special “Festschrift Issue” includes a tribute article to Bowman.

“These are all great honors to me,” says Bowman, who turned 65 this year and has no plans to retire. “Right now, I’m at the top of my game, the sweet spot of my career,” he says, citing four major research grants currently funding his group’s work.

Theoretical chemists do not work with chemicals: They write equations, analyze data and develop simulation models for molecular behaviors. It tends to be “a mature field,” Bowman says, where researchers hit their stride after years of experience, patience and perseverance.

Bowman is considered “one of the founding fathers of theoretical reaction dynamics,” the tribute authors write. (Click here to read the whole article, and more highlights from his career.) More recently, they add, he has made exceptional contributions to modeling potential energy surfaces, or PESs: “Without the PESs emerging from Joel’s group, many theorists would be unable to apply powerful methods of modern quantum dynamics to some of the most challenging problems of great current interest.”

Those problems include the molecular dynamics of water, a puzzle that particularly intrigues Bowman these days. During that cross-country plane flight, while most other passengers were probably trying not to think about things like turbulence and a stormy sky, Bowman took out his iPhone to make a video of lightning shooting through dark clouds (see below).

“What’s going on inside a cloud is extremely complicated, involving chemistry, physics, fluid dynamics and heat transfer, among other things,” Bowman says. “Clouds are full of energy, but parts of them can be cold while other parts are warming up. That’s a recipe for turbulence. Suddenly you can get a violent storm and boom! And all the action is taking place in what seems like just a simple little cloud. It’s mostly water.”

Currently, weather forecasting depends greatly on receiving continuous data from satellites and observing approaching fronts and other activity. “We can measure wind direction, high-and-low pressure, and use that information to create models, but that’s not nearly the level of data my research focuses on,” Bowman says.

Potential energy surfaces describe how water molecules bind together, and how much energy it takes to break them up into individual molecules.

“Imagine how sensational it would be if we could predict where and when a cloud will form,” Bowman says. “We’re getting closer to that ability, but we’re not there yet.”

Solving these kinds of puzzles could not only improve the accuracy of 10-day weather forecasts, it could help us predict long-term climate change, he says. “We don’t currently have the knowledge or the theoretical tools to fully understand what our climate will be like 20 to 30 years from now.”

Bowman is also exploring molecular mysteries underlying questions such as why we need water to live. “We know that we are made up of 70 to 80 percent water, and that without water, you cannot have life,” Bowman says. “And yet, from a chemical standpoint, we don’t really understand how water molecules interact with biological systems.”

"When I look at clouds, all kinds of questions come to my mind," Bowman says. Photo by Bryan Meltz, Emory Photo/Video.

Bowman joined Emory in 1986, during a time of rapid growth for the chemistry department. He has served as department chair, and helped establish Emory’s Emerson Center for Scientific Computation, becoming its acting director from 1991 to 1993. The center’s supercomputers are crucial to the Bowman Group’s work.

“Computer power has changed the field enormously,” Bowman says. “We can address problems and think about complicated chemical reactions in ways that people couldn’t dream of 20 years ago. Today, the computer winds up being almost like a laboratory where you can go in and do experiments.”

One challenge is to formulate the right question and get it onto the computer in a reasonable way, Bowman says. “Once you find the right question, and pose it correctly, getting the answer is often fairly straight-forward. Of course, then you have to interpret and understand the result that the computer spits out.”

While many of Bowman’s high-impact publications are collaborations with experimentalists, the theoretical work often begins with three or four members of his group sitting at a round table in his office, discussing a problem. “For me, the biggest joy is bouncing ideas around with my students and post-docs, questioning what’s known,” Bowman says. “And, of course, the discovery of things is a thrill. I get so excited they have to calm me down sometimes.”

Theoretical chemistry “is such a complex subject, involving math, physics, chemistry and computer science,” Bowman says. “Rather than intense focus on one thing, it involves carrying around a lot of data in your brain and thinking about many different things at the same time. That’s why when I look at clouds, all kinds of questions come to my mind and I start scratching my head.”

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Chemists modify rules for reaction rates

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