The size-selective vibrational spectrum of Si4Xe+ in the 240-500 cm(-1) range has been recorded using infrared (IR) multiple photon dissociation spectroscopy. Comparison to linear IR absorption spectra of Si-4(+) and Si4Xe+ calculated using density functional theory including dispersion corrections reveals an important influence of the Xe ligand on the structure of the cluster, involving significant charge transfer and formation of an incipient chemical Si-Xe bond with D-e = 03 eV. (C) 2012 Elsevier B.V. All rights reserved.