title: Infrared spectroscopy of Li(NH3)n clusters for n=4-7.
abstract: Infrared spectra of Li(NH3)(n) clusters as a function of size are reported for the first time. Spectra have been recorded in the N-H stretching region for n=4-->7 using a mass-selective photodissociation technique. For the n=4 cluster, three distinct IR absorption bands are seen over a relatively narrow region, whereas the larger clusters yield additional features at higher frequencies. Ab initio calculations have been carried out in support of these experiments for the specific cases of n=4 and 5 for various isomers of these clusters. The bands observed in the spectrum for Li(NH3)(4) can all be attributed to N-H stretching vibrations from solvent molecules in the first solvation shell. The appearance of higher frequency N-H stretching bands for n > or =5 is assigned to the presence of ammonia molecules located 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(NH3)(n) is complete at n=4. They are also consistent with neutron diffraction studies of concentrated lithium/liquid ammonia solutions, where Li(NH3)(4) is found to be the basic structural motif.
authors.affiliation: Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom.
authors.forename: Tom E
authors.initials: TE
authors.lastname: Salter
authors.forename: Victor A
authors.initials: VA
authors.lastname: Mikhailov
authors.forename: Corey J
authors.initials: CJ
authors.lastname: Evans
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Ellis