{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,3]],"date-time":"2026-10-03T02:28:15Z","timestamp":1790994495379,"version":"4.1.0"},"reference-count":29,"publisher":"National Academy of Sciences","issue":"2","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[1999,1,19]]},"abstract":"<jats:p>\n                    Ultrafast electron diffraction is a unique method for the studies of structural changes of complex molecular systems. In this contribution, we report direct ultrafast electron diffraction study of the evolution of short-lived intermediates in the course of a chemical change. Specifically, we observe the transient intermediate in the elimination reaction of 1,2-diiodotetrafluoroethane (C\n                    <jats:sub>2<\/jats:sub>\n                    F\n                    <jats:sub>4<\/jats:sub>\n                    I\n                    <jats:sub>2<\/jats:sub>\n                    ) to produce the corresponding ethylene derivative by the breakage of two carbon\u2013iodine, C\u2014I, bonds. The evolution of the ground-state intermediate (C\n                    <jats:sub>2<\/jats:sub>\n                    F\n                    <jats:sub>4<\/jats:sub>\n                    I radical) is directly revealed in the population change of a single chemical bond, namely the second C\u2014I bond. The elimination of two iodine atoms was shown to be nonconcerted, with reaction time of the second C\u2014I bond breakage being 17 \u00b1 2 ps. The structure of the short-lived C\n                    <jats:sub>2<\/jats:sub>\n                    F\n                    <jats:sub>4<\/jats:sub>\n                    I radical is more favorable to the classical radical structure than to the bridged radical structure. This leap in our ability to record structural changes on the ps and shorter time scales bodes well for many future applications in complex molecular systems.\n                  <\/jats:p>","DOI":"10.1073\/pnas.96.2.338","type":"journal-article","created":{"date-parts":[[2002,7,26]],"date-time":"2002-07-26T10:32:33Z","timestamp":1027679553000},"page":"338-342","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":72,"title":["Ultrafast electron diffraction and direct observation of transient structures in a chemical reaction"],"prefix":"10.1073","volume":"96","author":[{"given":"Jianming","family":"Cao","sequence":"first","affiliation":[{"name":"Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hyotcherl","family":"Ihee","sequence":"additional","affiliation":[{"name":"Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ahmed H.","family":"Zewail","sequence":"additional","affiliation":[{"name":"Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"341","published-online":{"date-parts":[[1999,1,19]]},"reference":[{"key":"e_1_3_3_1_2","volume-title":"Femtochemistry and Femtobiology: Ultrafast Reaction Dynamics at Atomic-Scale Reaction","author":"Sundstr\u00f6m V","year":"1997","unstructured":", ed V Sundstr\u00f6m (World Scientific, Singapore Femtochemistry and Femtobiology: Ultrafast Reaction Dynamics at Atomic-Scale Reaction, 1997)."},{"key":"e_1_3_3_2_2","volume-title":"Ultrafast Chemical and Physical Processes in Molecular Systems","author":"Chergui M","year":"1996","unstructured":", ed M Chergui (World Scientific, Singapore Ultrafast Chemical and Physical Processes in Molecular Systems, 1996)."},{"key":"e_1_3_3_3_2","volume-title":"Femtosecond Chemistry","author":"Manz J","year":"1995","unstructured":", eds J Manz, L W\u00f6ste (VCH, New York Femtosecond Chemistry, 1995)."},{"key":"e_1_3_3_4_2","volume-title":"Femtochemistry: Ultrafast Dynamics of the Chemical Bond","author":"Zewail A H","year":"1994","unstructured":"A H Zewail Femtochemistry: Ultrafast Dynamics of the Chemical Bond (World Scientific, Singapore, 1994)."},{"key":"e_1_3_3_5_2","doi-asserted-by":"crossref","unstructured":"Castleman A. 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