Stepwise hydration of ionized acetylene trimer. Further evidence for the formation of benzene radical cation

We report the thermochemistry of the stepwise hydration of the acetylene trimer ion ( C 2 H 2 ) 3 + using the drift tube technique. The binding energies and entropy changes for the addition of 1–7 water molecules to ( C 2 H 2 ) 3 + are identical to the corresponding values for the hydration of the benzene radical cation. The ( C 2 H 2 ) 3 + ion undergoes proton transfer within the ( C 2 H 2 ) 3 + ( H 2 O ) n clusters with n ⩾ 4. The proton affinity (211 kcal/mol) of the radical generated by the deprotonation of the ( C 2 H 2 ) 3 + ion is similar to that of the phenyl radical ( C 6 H 5 ) . Thus, the formation of the benzene ion is further confirmed in the ionized acetylene clusters.