Indication for a change of dynamics in plastic crystal chloroadamantane:: Raman scattering experiment and molecular dynamics simulation

Raman scattering experiment and molecular dynamics simulation have been performed on orientationally disordered crystal chloroadamantane. This investigation shows clear indication for a change of vibrational dynamics in the frequency range (2 cm(-1)-230 cm(-1)) at the temperature T-x corresponding to the onset of non-exponential relaxation and consistent with previous NMR and MD studies. This allows us to support the existence of a 'landscape-influenced' regime above the critical temperature T-c of the mode coupling theory. Convincing experimental evidence of local orientational ordering which can be nicely probed from the so-called bending mode of the chloroadamantane molecule are also given.