Infrared spectra of matrix-isolated sodium and potassium cyanides

The infrared spectra of matrix-isolated sodium and potassium cyanides in neon, argon, krypton, and nitrogen matrices were examined over the range 4000 cm^?1 to 33 cm^?1. The effect of temperature cycling, which normally results in migration of trapped molecules to generate polymeric species, has been pursued. A careful study of the effect of superheating the vapor species on the spectra has also been carried out. By these means it has been possible to identify the bands in the spectrum due to monomeric and polymeric species. Isotopic frequency shifts were measured for a ¹³C-enriched sample of sodium cyanide and ¹³C- and ¹⁵N-enriched samples of potassium cyanide. From the measured isotopic shifts it was possible to determine the structure of these two compounds as being linear NaCN and KCN. Accurate force constants were calculated using the measured frequency values for the three fundamental vibrational modes of the different isotopic molecules of NaCN and KCN. Bands due to sodium and potassium cyanates were also identified in some of these systems. ¹³C and ¹⁵N isotopic frequency shifts were also observed for NaOCN and KOCN.