Knowledge Bank

“The infrared absorption spectra of the gaseous dichlorides of iron, cobalt, and nickel and of nickel bromide display two absorptions in the region of the asymmetric stretching frequency. The stronger, higher frequency member of the pair has been observed in emission experiments on unsaturated vapors, and is assigned to the asymmetric stretch of the presumably linear monomer. The weaker transition is assigned to a vibrational mode of the dimeric molecule. The observed frequencies are $FeCl2,490cm-1;CoC12-492cm-1$; $NiCl2,-505cm-1$; and $CoBr2,-397cm-1$. Force constants of the three dichlorides calculated from these frequencies agree with those of the diatomic monochlorides to 0.1 $millidynes/A2$.”