Number 62 (Story #3), January 10, 1992 by Phillip F. Schewe and Ben Stein FEMTOCHEMISTRY is the study of chemical reactions with a time resolution of femtoseconds. Ahmed H. Zewail and his colleagues at Caltech use two lasers to both excite and observe the reaction of xenon atoms with iodine molecules. The timing of the laser pulses can be adjusted to modulate the yield of reaction products. (Nature, 2 Jan. 1992.)