Zewail, zuh WAYL, Ahmed Hassan (1946-...), won the 1999 Nobel Prize for chemistry for his experiments showing how molecules change during chemical reactions. In such reactions, chemical bonds (attractions between atoms that make up molecules) form and break extremely rapidly. And in many cases, what seems to be a single reaction actually takes place in two or more steps. Zewail and his colleagues at the California Institute of Technology (Caltech) in Pasadena developed the first experimental techniques that are fast enough to detect such steps and measure their speed. In these techniques, brief pulses of laser light produce and measure the reactions.