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Updated: Aug 7, 2026

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
Published on: March 22, 2019
Infrared spectroscopy of Li(NH3)n clusters for n=4-7
Tom E Salter1, Victor A Mikhailov, Corey J Evans
1Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom.
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.
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