NEW TOOL TO TAKE MOLECULAR MOVIES

Abstract

IN A STRIKING EXAMPLE OF THE power of a new ultrafast diffraction technique, scientists have probed the evolving structure of an excited molecule as it decays and have discovered a previously unknown structural intermediate in the process. A group at California Institute of Technology headed by Nobel Laureate and ultrafast chemistry pioneer Ahmed H. Zewail has used electron diffraction to show that a pyridine molecule excited into a special state sheds its excess energy by opening up its ring—something never before predicted [ J. Phys. Chem. A , 105, 11159 (2001)]. Ordinary electron diffraction techniques give distances between nuclei, revealing the structure of a compound. But ZewaiTs group has developed a methodology with an instrument—whose construction was funded by NSF—that repeatedly takes electron diffraction snapshots of a reacting system every fraction of a picosecond. Its success in producing such a detailed chemical movie has exceeded Zewail's expectations. It's so clean and neat—usually exp...