The 1999 Nobel Laureate for chemistry will speak at Ohio State at 3:30 p.m. Wednesday at the McPherson Chemical Laboratory.Ahmed Zewail, a professor of chemistry and physics at the California Institute of Technology, will speak at the 38th Annual William Lloyd Evans Lecture. It was announced two weeks ago that Zewail had won the Nobel Prize for his work using laser spectroscopy to determine exactly how chemical reactions occur. Selecting a Nobel Laureate to give the Evans Lecture is not new for the chemistry department. In fact, of the 38 people who have presented the lecture since it began in 1961, 17 of them were Nobel Laureates, and nine won the award within two years of giving the lecture at Ohio State. The subject of Zewail’s lecture is chemistry and biology in the femtosecond age. A femtosecond is equal to a millionth of a billionth of a second, said Sherwin Singer, associate professor of chemistry and this year’s coordinator of the Evans Lecture.The first experiments with femtoseconds began in the early 1980s. Until then, the smallest amount of time scientists had been able to use in experiments was a picosecond, which is 0.000000000001 seconds. “Chemists have had to make judgments about how reactions occur through inference. With this technology, we can see how the reactions occur in real time,” Singer said.Bern Kohler, an assistant professor of chemistry, said that it is easiest to conceptualize how small a femtosecond is by putting it on a larger scale.”A femtosecond is to one second as one second is to 32 million years,” Kohler said. Terry Gustafson, also an associate professor of chemistry, said he recognizes the significance of Zewail’s work. “Zewail’s work is important because understanding it helps us predict chemical reactions we don’t know, such as those of a new molecule,” Gustafson said. “Predicting reactions is the theme of what we do in chemistry.”Before femtochemistry, scientists knew very little about what happened during the course of chemical reactions. They knew the reactants and the products, but the reaction happened too quickly to understand what happened in between, Gustafson said. According to Singer, the development of femtochemistry has made it possible for scientists to watch the complete chemical reaction as if it were a movie unfolding.Aside from the Nobel Prize, Zewail has won several awards, including the Leonardo Da Vinci Award of Excellence, the King Faisal Prize and the Linus Pauling Medal, among others.Kohler and Claudia Turro, assistant professor of chemistry, who do research similar to Zewail’s, will also present short lectures about their research from 2 to 3 p.m. in McPherson Lab room 1015. Their lectures will be followed by an opportunity to meet Zewail in McPherson Lab room 1023 from 3 to 3:30 p.m. Zewail’s lecture will then take place in McPherson Lab room 1000.