Infrared Study of Matrix-Isolated Lithium Isocyanide

Abstract

The infrared spectrum of lithium isocyanide trapped in solid matrices of neon, argon, and nitrogen was examined over the range 4000–33 cm−1. The effect of temperature cycling, which results in migration of trapped molecules to generate polymeric species, has been pursued. A careful study of the effect on the spectra of superheating the vapor species has been carried out. By these means it has been possible to identify the bands in the spectrum due to monomeric and to polymeric species. This paper is only concerned with the monomeric species. Isotope frequency shifts were measured for carbon-13, nitrogen-15, and lithium-6 enriched samples of lithium isocyanide. From the measured isotopic shifts it was possible to determine the structure of the monomer of the lithium compound as being linear LiNC. Accurate force constants were calculated using the measured frequency values of the three fundamental vibrational modes of the different isotopic molecules of LiNC.