Knowledge Bank

Mass-selected infrared spectra of the uncharged metal-solvent clusters Li(NH$3$) in the N-H stretching region have been recorded using IR photodepletion spectroscopy. The bands observed in the IR spectra for Li(NH$3$)$4$ have been assigned to N-H stretching vibrations from solvent molecules located in the first solvent shell. The appearance of higher frequency N-H stretching bands for {\it n} $\ge$ 5 is attributed to one or more ammonias in a second solvent shell. These data provide strong support for previous suggestions based on gas-phase photoionization measurements that the first solvation shell for Li(NH$3$) is complete at {\it n} = 4. They are also consistent with neutron diffraction studies of concentrated lithium-liquid ammonia solutions, where quasi-tetrahedral Li(NH$3$)$4$ is found to be the basic structural motif. Our spectra will be presented alongside computational predictions of the cluster spectra.