ANTIFERROMAGNETIC ORDERING EFFECT ON LIGHT ABSORPTION SPECTRUM BY CRYSTALLINE OXYGEN

The optical “double” transition spectrum of crystalline oxygen is studied in the frequency range of 15000 to 31000 cm−1 at different temperatures (5 to 27 °K) and nitrogen concentrations (0 to 40%). A sharp integral intensity decrease of the absorption bands, their shift, and broadening are found in the temperature range investigated. With the insertion of nitrogen into oxygen new absorption bands with spectral positions close to the pure oxygen band frequencies appeared in the oxygen spectrum. The results show that the “double” transitions in oxygen are considerably induced by exchange interaction. It is also shown that the O−0 band intensity of the 23 Σ g− → 21Δg and 23Σ g− → 21 Σ g+ transition is determined by the interaction not with acoustic phonons, as it was considered before, but with magnons corresponding to the Brillouin zone boundary and having an energy equal to the exchange one gμBHE. The O−0 band of the 23Σ g− → 1Δg + 1Σ g+ transition is interpreted as a pure electronic band. A consistent scheme, based on considering the exchange splitting of the 3Σ g− ground state of the oxygen molecules and the magnon excitation at light absorption is suggested to explain the “double” transition structures and their band behaviours at magnetic ordering. Copyright © 1968 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim