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September 23, 2020

Professor recognized for work on photochemistry

By MEDHA KALLEM | February 13, 2020

David Yarkony, D. Mead Johnson professor of Chemistry and chair of the department, received the American Chemical Society (ACS) Award in theoretical chemistry for 2020 last month, and will be honored in San Francisco this year. 

The award is given by the Physical Chemistry Division of the ACS in order to recognize members of the society who have made significant contributions to their fields of research. 

The ACS is a national organization that provides a platform for chemists to network, develop their careers and fund their work. It promotes the development of the field of chemistry, and for people like Yarkony, provides them with recognition for dedication to their work.

The Yarkony Group focuses its research primarily on the characteristics of conical intersections of adiabatic surfaces. Conical intersections are instances where the Born-Oppenheimer Approximation fails. 

This quantum chemical approximation proposes that the motion of the electrons of an atom can be separated from the motion of the nucleus, based on the fact that electrons are small and move more rapidly than the dense, slow nucleus. 

The Born-Oppenheimer Approximation is used in conjunction with the Schrodinger equation to create the wave function that characterizes a system. Since the Born-Oppenheimer Approximation is not applicable at conical intersections, both the motion of the nucleus and the motion of the electrons have to be considered. 

Although often thought to be a rare occurrence, the break down of the Born-Oppenheimer Approximation is actually common in chemistry and understanding the nature of this break down can be extremely useful in furthering research in areas such as photochemistry and solar energy conversion.

In an interview with The News-Letter, Yarkony explained that he happened upon conical intersections about 20 years ago and decided to focus on studying them.

“It was about being in the right place at the right time with the right tools,” he said. 

In the late 1980s to 1990s, one of the major problems in computational chemistry was whether or not Oppenheimer potential energy curves actually crossed. It turned out that Yarkony had already written a program to calculate coupling between adiabatic states and had discovered that the crossings were indeed present. 

“I changed the paradigm for photochemistry. It used to be thought that the curves got close together, but never crossed. Now the paradigm is that they crossed. It changed what people looked for and how they treated that important problem,” he said. 

Yarkony discussed the difficulties of being a researcher. Since the work is inherently novel, it minimizes the number of resources one has when they hit a roadblock in their work. 

“Since these are the first programs that do this, you can’t call up your friend and ask ‘What did you get for this problem?’” Yarkony said. 

Regardless of how challenging his work could be at times, Yarkony has persisted through it all. Yarkony said that his passion for his work is derived from his desire to give back to the scientific community. 

“I wanted to get through the difficulties because I had already spent a couple years writing the programs, and I wanted to make sure they do something useful,” he said. 

Yarkony is proud to say that he has achieved that goal. To him, receiving the ACS award is validation for his perseverance. 

“It shows that people out in the real world appreciate what I’ve done. I’ve worked on this from 1990 and I get to hear someone say ‘Good job David,’” he said. 

Yarkony continues to have great ambitions for the future. In the 1980s, he wrote a program to treat relativistic effects in molecular science. He left this project to focus on his research on conic intersections. Now he aims to combine both projects. 

“There’s two types of radiationless decay. There’s the stuff through conic intersections and the stuff that goes through spin orbit coupling,” he said. “For a full picture, you have to treat them both.” 

The Yarkony group hopes to next write new programs for spin orbit coupling in order to further the scientific community’s understanding of nonadiabatic processes. One goal is to expand the number of molecules their programs can be applied to. 

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