IR Spectroscopic Characterization of Methane Adsorption on Copper Clusters Cu n + ( n = 2-4).

The interaction of CH 4 with cationic copper clusters has been studied with infrared-multiple photon dissociation (IRMPD) spectroscopy. Cu n + ( n = 2-4) formed by laser ablation were reacted with CH 4 . The formed complexes were irradiated with the IR light of the free-electron laser for intracavity experiments (FELICE), and the fragments were mass-analyzed with a reflectron time-of-flight mass spectrometer. The structures of the Cu n + -CH 4 complexes are assigned on the basis of comparison between the resulting IRMPD spectra to spectra of different isomers calculated with density functional theory (DFT). For all sizes n , the structure found is one with molecularly adsorbed CH 4 . Only slight deformations of the CH 4 molecule have been identified upon adsorption on the clusters, which results in redshifts of the spectroscopic bands. This deformation can be explained by charge transfer from the cluster to the adsorbed methane molecule.