The inelastic neutron scattering (INS) spectrum of [1.1.1.1]-pagodane is presented through 1600 cm(-1). The INS spectrum is divisible into a region of well-resolved vibrational features (200-750 cm(-1)) and a second region of overlapping transitions (750-1600 cm(-1)) that contains the majority of all molecular modes. Comparison of the INS spectrum with a B3LYP/6-31G** calculation for the isolated molecule reveals notable differences in several low frequency modes while generally agreeing at higher frequency. Periodic density functional theory (DFT) calculations are employed to determine whether intermolecular interactions are the origin of these differences between the B3LYP/6-31G** and INS spectra. (C) 2004 Elsevier B.V. All rights reserved.