15min:

RACHAEL A. RELPH, JOSEPH C. BOPP, JOSEPH R. ROSCIOLI, MARK A. JOHNSON, Sterling Chemistry Laboratory, Yale University, PO Box 208107, New Haven, CT 06520.

Infrared predissociation spectroscopic studies of systematically solvated acetylene clusters, (C₂H₂)_n⁺, n = 1-4, reveal the structural evolution of these cations with increasing cluster size. The argon predissociation spectrum of the acetylene dimer coupled with harmonic frequency calculations suggests the dominate species adopts a cyclobutadiene-like geometry. The argon solvated trimer, (C₆H₆)⁺ Ar, predominantly loses (C₂H₂)⁺ Ar, suggesting that the trimer is composed of a covalently bonded ``dimer core'' which exhibits a spectrum different than cyclobutadiene, and is solvated by a weakly bound acetylene. The same spectral features are retained in the tetramer suggesting that the dimer core survives the solvation of additional acetylene molecules. The minor loss channel of (C₆H₆)⁺ Ar, loss of a single Ar, shows multiple features believed to be from a number of covalently bonded (C₆H₆)⁺ species.