Issue 1, 2002

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

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.

Article information

Article type
Paper
Submitted
03 Sep 2001
Accepted
05 Nov 2001
First published
17 Dec 2001

Phys. Chem. Chem. Phys., 2002,4, 34-42

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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