Inelastic neutron scattering and DFT study of 2-amino-3-hydroxymethyl-1,3-propane diol (TRIS)

We report an inelastic neutron scattering (INS) study of 2-amino-3-hydroxymethyl-1,3-propane diol (TRIS). The assignment of the experimental vibrational spectra measured using several incident neutrons' energies on HRMECS spectrometer has been made by means of DFT calculations. To simulate crystal environment both molecular cluster and solid state models were used. The study has been completed by an alternative approach, molecular dynamics (MD) calculations, done at the same level of the DFT theory. The INS spectra calculated with the solid state models (normal mode analysis, and MD) gave a better fit of the experiment than the cluster model. On the other hand, the peaks between 650 and 850 cm^-1 in the experimental INS spectra assigned to OH torsional modes were reproduced better by the cluster calculations. The nature of the stretching frequency of unusually long O-H bond (1.012 Å) was interpreted by means of MD calculations. The interpretation of the spectrum below 100 cm^-1 was based on Fourier transform of the velocity autocorrelation function of centre of mass of a molecule of TRIS.