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Issue 1, 2002
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The photochemistry of 1,4-cyclohexadiene in solution and in the gas phase: conical intersections and the origin of the ‘helicopter-type’ motion of H2 photo-generated in the isolated molecule

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Abstract

The complex photochemistry of 1,4-cyclohexadiene (CHDN) in solution and in the gas phase is analyzed using a model postulating the involvement of conical intersections. Several conical intersections are found for this system, using a method based on the Longuet–Higgins phase-change rule. The energies and structures of the conical intersections and of some key intermediates are calculated using quantum chemical methods. A single conical intersection, the H/allyl one, is shown to account qualitatively for all the products observed in solution, and also for the cleavage of a H-atom observed in the gas phase. The model is also consistent with the isotopic distribution in the products of deuterated CHDN. The helicopter-type motion of the H2 product observed in the collision-free photolysis of CHDN by E. V. Cromwell, D.-J. Liu, M. J. J. Vrakking, A. H. Kung and Y. T. Lee (J. Chem. Phys., 1991, 95, 297 []), is not compatible with the properties of this conical intersection. A different one, which is shown to lead naturally to such motion is proposed, and its properties are calculated.

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Article information


Submitted
03 Sep 2001
Accepted
05 Nov 2001
First published
17 Dec 2001

Phys. Chem. Chem. Phys., 2002,4, 34-42
Article type
Paper

The photochemistry of 1,4-cyclohexadiene in solution and in the gas phase: conical intersections and the origin of the ‘helicopter-type’ motion of H2 photo-generated in the isolated molecule

S. Zilberg and Y. Haas, Phys. Chem. Chem. Phys., 2002, 4, 34
DOI: 10.1039/B107991N

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