Raman study of orientational disorder in the molecular charge-transfer crystals naphthalene-TCNB and naphthalene-PMDA

We have studied orientational disorder in the molecular charge-transfer crystals naphthalene-tetracyanobenzene (N-TCNB) and naphthalene-pyromellitic dianhydride (N-PMDA) by Raman scattering from low frequency intermolecular modes. From the temperature dependence of intensities and linewidths we find strong evidence for an order-disorder transition in naphthalene-TCNB at 63 K in which the center of symmetry is removed. In naphthalene-PMDA, on the other hand, the spectrum is consistent with an ordered structure in which the molecules exhibit anharmonic motion at high temperatures. Copyright © 1977 American Institute of Physics.