Geometric Phase in Chemical Reactions

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Science  19 Aug 2005:
Vol. 309, Issue 5738, pp. 1195-1196
DOI: 10.1126/science.1117201

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A quantum mechanical effect known as geometric phase can sometimes influence simple chemical reactions. This phenomenon, also known as the Berry phase, results in a change in the sign of a quantum wave function as atomic nuclei move around the potential energy surfaces during the reaction. In his Perspective, Clary discusses an analysis reported in the same issue by Juanes-Marcos et al. of the geometric phase effects on the hydrogen exchange reaction H + HH+ H. Some calculations have shown that geometric phase should affect the outcome of the reaction, whereas others that ignore the effect have been in good agreement with experiment. In fact, the effect due to the geometric phase undergoes a subtle cancellation that the authors can now explain by means of topological arguments.