Ahmed H. Zewail had been fighting a cold all weekend. But when he received a pre-dawn phone call from the Royal Swedish Academy of Sciences informing him he had just won the Nobel Prize in chemistry, his symptoms suddenly disappeared.

Zewail, a professor at the California Institute of Technology, wasn’t honored for discovering a cure for the common cold, but for pioneering a technique to view the motion of atoms in a chemical reaction. He developed what is basically the world’s fastest camera. Using quick laser flashes, the camera operates at the time scale at which chemical reactions take place ? femtoseconds.

Named for the Danish word for fifteen, a femtosecond is 10-15 seconds. How fast is a femtosecond? It is to one second as a second is to 32 million years. In the words of the Nobel academy, “We have reached the end of the road: no reactions take place faster than this.” [1] Zewail’s work has given rise to a new branch of physical chemistry called femtochemistry.

The laser camera works by mixing two beams of molecules in a vacuum chamber. The laser then injects two pulses. The first, a pump pulse, excites the molecule to a higher energy state. The second, a probe pulse, detects either the original molecule or an altered form, depending on the wavelength. Researchers can vary the time interval between the two pulses to determine how long it takes for the molecule to be transformed.

Before the development of femtochemistry, researchers could only theorize about how atoms collide and combine. But the laser camera enables scientists to view chemical reactions in slow motion, similar to the way we might watch a slow motion replay in a football game. As a result they have solved some long-standing mysteries about chemical reactions. Among the questions they have answered are why some reactions take place while others don’t, and how temperature controls the speed of reactions.

Since Zewail’s breakthrough work in the late 1980s, research in femtochemistry has taken off throughout the world. Current studies are investigating:

• molecular activity during photosynthesis, as chlorophyll converts sunlight into usable energy
• how catalysts trigger chemical reactions
• the mechanisms involved when a substance is dissolved in a liquid

Following Zewail’s research, scientists are glimpsing physical and biological processes at a level that was once beyond human ability. In the future we may see the development of new polymers for industry, or new and more effective medicines, thanks to this deeper understanding of chemical reactions.

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