Density functional B3LYP and ab initio G3(MP2,CCSD)//B3LYP calculations have been performed to study isomerization and dissociation pathways of C6H123+ in relation to the Coulomb explosion mechanism of cyclohexane. Cyclohexane trication is found to be metastable kinetically as the highest barrier on its decomposition pathway corresponding to the 2,1-H shift in the initial open-chain intermediate formed spontaneously after multiphoton ionization of cyclohexane is only 3.0 kcal/mol. The most favorable dissociation channels lead to the C4H82+ + C2H4+, C5H92+ + CH3+, and C3H62+ + C3H6+ products and all of them share the same reaction step with the highest barrier. (C) 2004 Elsevier B.V. All rights reserved.