Rapid condensation of acetylene onto the benzene cation with the addition of up to eight acetylene molecules is observed in the gas phase at 120-140 K forming the C6D6 center dot+(C2H2)(n) clusters. The binding energies and entropy changes of the stepwise condensation of the first four acetylene molecules onto the benzene cation have been measured and correlated with the calculated lowest energy isomers. The measured binding energies (3-4 kcal/mol) reflect weak charge-induced dipole and (benzene) C-H delta+center dot center dot center dot pi C C (acetylene) hydrogen bonding interactions. Associative charge transfer is suggested to activate the cyclization of three acetylene molecules to form a benzene molecule (C6H6). (C) 2011 Elsevier B.V. All rights reserved.