Infrared Spectra of Sodium and Potassium Cyanide

Abstract

The infrared absorption spectra of sodium cyanide and potassium cyanide vapors have been measured in the region 3500 to 200 cm^‐1. Two absorptions assigned as fundamental frequencies of the monomeric species were found in each system. The absorption frequencies and their present assignments are: NaCN ν₂=238, ν₃=2176 cm^‐1; KCN ν₂=207, ν₃=2158 cm^‐1. A third absorption at 2076 cm^‐1 in sodium cyanide vapor is assigned to the dimer of NaCN. The bond‐stretching force constant of the CN group in XCN molecules is sensibly independent of the electronegativity of X. The angle‐bending force constant varies directly with the electronegativity of X.