The vibration spectra of crystals - Part IV. Magnesium Oxide
The nine fundamental frequencies of the magnesium oxide structure ate theoretically evaluated. Expressed as infra-red wave-lengths, they are respectively 14·2, 14·7, 15·35, 17·1, 19·0, 21·1, 23·4, 38·8 and 54·4 μ. All except the last two are active in the infra-red and their positions cheek very closely with the absorptions observed by Barnes and Brattain, by Strong and by Fock. The octaves of the first seven fundamentals and numerous summational frequencies including also the two inactive fundamentals have been identified with the lines recorded by Barnes aud Brattain in the absorption spectrum of cleavage plates of various thicknesses.