Inelastic neutron scattering has been used to characterize the vibrational spectroscopy below 220 meV of para-nitroaniline adsorbed in the molecular sieve ALPO-5. Samples at loadings of both 3 and 13 weight %, which represent the onset of and the maximum in the nonlinear optical properties respectively, were studied. The torsional vibration of the amino (NH2) group has been identified at ca. 50 meV. The splitting and structure of this mode is sensitive to the loading level. This can be related to differences in the nature of the hydrogen bonding in these materials.