The First Femtosecond in the Life of a Chemical Reaction

摘要

When light initiates chemical change— such as photosynthesis in plants, or vision in an eye, or the formation of vitamin D in your skin—the fust stages happen with breathtaking rapidity Elections in molecules can absorb a photon and rearrange in only femtoseconds (a femtosecond is 10~(-15) s). A bedrock of chemical theory known as the Franck-Condon principle assumes that such short times are so infinitesimal that for all practical chemical purposes they are instantaneous: All the atoms in a molecule remain frozen during the critical instant of electron transition.