STOCKHOLM, Sweden (AP) _ Egyptian-born scientist Ahmed E. Zewail of the California Institute of Technology won the Nobel Prize for chemistry today for demonstrating that a rapid laser technique can observe the motion of atoms in a molecule as they occur during a chemical reaction.

The Royal Swedish Academy of Sciences said he was being honored for a revolution in chemistry through ``his pioneering investigation of fundamental chemical reactions, using ultra-short laser flashes, on the time scale on which the reactions actually occur.

Hours earlier, Dutch scientists Gerardus 't Hooft and Martinus J.G. Veltman won the 1999 Nobel Prize for physics for their theoretical work on the structure and motion of subatomic particles.

The academy said Zewail's work in the late 1980s led to the birth of femtochemistry, the use of high-speed cameras to monitor chemical reactions.

``We have reached the end of the road. No chemical reactions take place faster than this,'' the academy said.

``We can now see the movements of individual atoms as we imagine them. They are no longer invisible,'' the academy said.