In search of low-energy excitations in rigid molecular crystals, the available heat capacity, C-p, data of 85%C-60-15%C-70 (wt %) mixture at temperatures in the 2-30 K range have been analyzed. It is found that its C-p/T-3 against T plot has an asymmetric peak centered at 4.5 K, which has the features of both the Boson peak and of the peak attributed to librations of guest molecules in clathrates. Appearance of a peak in the C-p/T-3 against T plot is a characteristic of the Einstein equation for random phase atomic motions. Most of the C-p of fullerenes at T<10 K is attributed to random phase librations of C-60 and C-70 molecules at their crystal sites. (C) 2003 American Institute of Physics.