EFFECT OF ORIENTATIONAL AND SUBSTITUTIONAL DISORDERS ON THE N2 VIBRATIONAL EXCITON IN N2 CO MIXED-CRYSTALS/

High resolution Raman spectroscopy was performed on the N2 vibron band s over a large concentration range at various temperatures in N2/CO mi xed crystals. The Davydov splitting appears for N2 concentration above 0.2 and linearly increases up to the pure crystal limit. The Raman li newidth exhibits a maximum for a N2 concentration of 0.15 and decrease s towards a residual value in the low concentration limit. Two types o f disorder for the asymmetric CO molecules. A Hamiltonian including co rrelated diagonal and off-diagonal disorder terms was suggested to des cribe the vibron band. The first moments of the Raman intensity were c alculated as a function of the concentration. The first moment account s for the linear dependence of the Davydov splitting in terms of the c oncentration. The second moment predicts the residual bandwidth in the low N2 concentration limit which is proved to result from the orienta tional disorder of the CO molecules.