Infrared Spectra of Gaseous Transition-Metal Dihalides

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Abstract
The infrared spectra of gaseous MnCl2, FeCl2, CoCl2, NiCl2, CuCl2, and CoBr2 have been measured in absorption between 220 and 4000 cm—1. With the exceptions of MnCl2 and CuCl2, the emission spectra of these molecules have also been obtained in this region. The emission from unsaturated vapor indicates that one of the two absorptions observed for each of the dihalides, other than manganous chloride, is attributable to a vibration of a polymeric species. Assuming that the monomeric dihalide molecules have D∞h symmetry, the monomeric absorption is assigned to ν3, the antisymmetric stretching vibration. The M—X bond stretching force constants calculated using the linear model and a simple valence force field are quite similar to those of the corresponding diatomic monohalides. Both sets of constants show a maximum between manganese and zinc.