Inelastic neutron scattering (INS) is crucial in the study of hydrogen storage where the neutron can excite the quantum motion of the H2 molecule, and measure the transition energies directly (see Chap. 8). However, in the more general case INS amounts to “vibrational spectroscopy with neutrons” and in the present book is used to study local structure, vibrational dynamics, and the nature of hydrogen-bonding interac­tions. The main strength of the technique arises from the large neutron-scattering cross section of hydrogen, which causes vibrations involving hydrogen to dominate the spectra. This domination, particularly when combined with selective deuteration, is very powerful for providing assignment of the observed peaks to specific
vibrational-modes. In addition, it is now straightforward to calculate the INS directly from a molecular model which is not only an aid to assignment, but also a validation procedure for the model. The technique is comparable to infra-red and Raman spectroscopy, which have better resolution, but lack the hydrogen selectivity and simplicity of assignment. Incoherent INS has no selection rules and even modes that are silent in both infra-red (IR) and Raman can have significant INS intensity.