Infrared spectroscopy has been applied to benzene-ethane clusters to investigate the preferential contact structures due to the CH/π interaction between an alkyl group and a single phenyl ring. Stable structure search of the clusters by high-level ab initio calculations has been also carried out. The observed infrared spectra are well accounted for by the presence of the isomer which has the monodentate structure. The speculated isomer with a tridentate structure has been ruled out by analyses of the observed infrared spectra and theoretical calculations.

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