Knowledge Bank

Infrared predissociation spectroscopic studies of systematically solvated acetylene clusters, (C$2$H$2$), $n=1-4$, 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, (C$6$H$6$)$+$ $\cdot$ Ar, predominantly loses (C$2$H$2$)$+$ $\cdot$ 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 (C$6$H$6$)$+$ $\cdot$ Ar, loss of a single Ar, shows multiple features believed to be from a number of covalently bonded (C$6$H$6$)$+$ species.