Infra-red spectra of ethylenediamine dihydrochloride and other amine hydrochlorides in alkali halide disks

The infra-red spectra of solids can be studied by the pressed-disk technique. This involves pulverizing a little of the sample with a powdered alkali halide and pressing in vacuo under pressure to give a transparent disk. The spectra observed using pressed disks sometimes differ markedly from those observed with other techniques. Ethylenediamine dihydrochloride and the three methylamine hydrochlorides were pressed with KCl, KBr, KI, NaCl and NaBr. The changes in their spectra were studied. The results obtained indicate that the changes are principally produced by hydrogen-bond type interactions. These occur between the physically adsorbed polar molecules and the negative ions Cl−, Br− and I− of the polycrystalline alkali halides.