Infrared spectroscopy of Li+(CH4)n, n = 1–9, clusters

We report the infrared spectra of Li+(CH4)n, n = 1–9, clusters in the C−H stretching region using vibrational predissociation spectroscopy. Vibrational frequencies and geometries were calculated at the B3LYP/6-31+G∗ level with zero-point corrected binding energies at the MP2/6-31+G∗ level. Experiments and calculations indicated a first solvent shell size of four CH4. Second solvent shell ligands were identified by smaller frequency shifts and changes in relative intensity, suggesting a reduced influence of Li+ beyond the first shell. Perturbation of the CH4 vibrational modes appears to be dominated by the Li+⋯CH4 electrostatic interaction, while CH4⋯CH4 interactions between first and second shell molecules have no measurable effect.