What can happen in a femtosecond? One millionth of a billionth (10-15) of a second—it’s a time scale that’s almost impossible to grasp. In 1 femtosecond light travels a distance much less than the thickness of a human hair, even less than the diameter of a bacterium. Give it an entire second, and light travels from the Earth to the Moon. Yet much of the chemistry vital for life punches a femtosecond time clock. The making and breaking of atomic bonds during every reaction in chemistry and biology passes through a transition state, which can be thought of as the moment at which the bond decides if it will break or reform. Movement of the surrounding atomic environment over a few femtoseconds has an equal probability of nudging atoms to form new products or of returning them to their original configuration. Because it is so short-lived, the transition state has always been a mystery to scientists who wanted to understand its role in the action of enzymes, the essential catalysts of life.
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