“…Therefore, in order to achieve a more realistic comparison with the measured spectra, the computed INS spectra are averaged over all possible orientations of C 60 , as described previously [18]. Moreover, with the IN4C spectrometer used by Horsewill and co-workers [16], the INS spectra of H 2 and HD in C 60 are recorded over a broad range of κ ≡ |κ| values. This means that S(κ, ω), obtained by averaging S(κ, ω) in equation (2.3) over all directions of the wavevector κ [18], needs to be integrated also over κ to obtain the desired S(ω), which is done below.…”