VIBRATIONAL-RELAXATION IN DISORDERED 1,4-DIHALOBENZENES

The influence of structural disorder on vibrational relaxation in molecular crystals has been investigated by using high resolution Raman spectroscopy. The role of the disorder has been studied by analyzing the temperature dependence of lattice and internal modes linewidths in two isomorphic benzene derivatives: the 1,4-C6H4BrCl (p-BCB) and the 1,4-C6H 4Br2 (p-DBB) crystals. The former shows a disorder arising from a random head-to-tail orientation of the molecular dipoles. It has been found that in p-BCB crystals the additional band broadening, ascribed to head-to-tail disorder, can be assumed to be temperature independent. It is shown that corresponding modes in the two crystals involve similar anharmonic decay processes. © 1995 American Institute of Physics.