Revisiting the von Neumann–Wigner noncrossing rule and validity of a dynamic correlation diagram method

• Published in: Journal of theoretical & computational chemistry Vol. 18; no. 2; p. 1950013
• Main Authors: Nohira, Hiroyuki, Nohira, Toshiyuki
• Format: Journal Article
• Language: English
• Published: World Scientific Publishing Company 01.03.2019
• Subjects: noncrossing rule; femtosecond scale; Correlation diagram; Dewar benzene; uncertainty principle
• ISSN: 0219-6336; 1793-6888
• DOI: 10.1142/S0219633619500135

The noncrossing rule for potential energy surfaces can be applied only, as originally postulated by von Neumann and Wigner, to slowly occurring changes; it has, however, over many years, been widely used to rationalize fast chemical reactions. Taking the conversion of Dewar benzene to benzene as an example, we demonstrate a reaction that has a timescale for which crossings are allowed. Since it is now established that elementary chemical reactions proceed over ca. 10–100 fs, as revealed experimentally by Zewail, the noncrossing rule cannot any longer be said to be valid for most chemical reactions. We further demonstrate that the mechanism of the chemiluminescent conversion of Dewar benzene to benzene is explained by an electronic state diagram derived using a dynamic correlation diagram method which allows crossings, whereas the reaction is not explained by a conventional approach, applying the noncrossing rule using a static correlation diagram method. We examine if the von Neumann-Wigner noncrossing rule is applicable for elementary chemical reactions. Taking the conversion of Dewar benzene to benzene as an example, we demonstrate a reaction that has a timescale for which crossings are allowed according to the von Neumann-Wigner criteria. We show that the mechanism of this chemiluminescent conversion reaction is explained best by an electronic state diagram derived using a dynamic correlation diagram method which allows crossings.