Ab initio/RRKM study of dissociation mechanism of C6H63+: A view on Coulomb explosion of benzene

Density functional B3LYP/6-31G(d,p) calculations have been performed in order to investigate isomerization and dissociation of benzene trication, which are relevant to the Coulomb explosion mechanism of benzene. The results demonstrate that the benzene-like isomer of C₆H₆³⁺ can decompose through various pathways leading to distinct fragmentation products. RRKM calculations of rate constants for individual reaction steps assuming that the initial internal energy of the trication is 110 kcal/mol and solving kinetic master equations to obtain relative branching ratios show that H₂CCCH²⁺ + H₂CCCH⁺ are the dominant products (81.5%) followed by C₂H₃⁺ + C₄H₃²⁺ (13.2%) and the other minor products include CH₃⁺ + H₂CCCCCH₂⁺ (2.6%), C₂H₄²⁺ + H₂CCCC+ (1.1%), H₂CCCH²⁺ + c-C₃H₃⁺ (0.55%), C₂H₂⁺ + c-C₄H₄²⁺ (0.49%), C₂H₄⁺ + HCCCCH²⁺ (0.20%), and CH₂⁺ + H₂CCCHCCH²⁺ (0.14%). The fragments are expected to be produced with high translational energy due to high Coulomb repulsion energy barriers. We consider implications of the C₆He₆³⁺ potential energy surface and decomposition mechanism to the Coulomb explosion of benzene.