  The superposition of the quantum rotational motion (tunneling) of the
encapsulated Sc2C2 complex with the classical rotational motion of the
surrounding C84 molecule in a powder crystal of Sc2C2@C84 fullerite is
investigated by theory. Since the quantum rotor is dragged along by the C84
molecule, any detection method which couples to the quantum rotor (in casu the
C2 bond of the Sc2C2 complex also probes the thermally excited classical motion
(uniaxial rotational diffusion and stochastic meroaxial jumps) of the
surrounding fullerene. The dynamic rotation-rotation response functions in
frequency space are obtained as convolutions of quantum and classical dynamic
correlation functions. The corresponding Raman scattering laws are derived, the
overall shape of the spectra and the width of the resonance lines are studied
as functions of temperature. The results of the theory are confronted with
experimental low-frequency Raman spectra on powder crystals of Sc2C2@C84 [M.
Krause et al., Phys. Rev. Lett. 93, 137403 (2004)]. The agreement of theory
with experiment is very satisfactory in a broad temperature range.
