EXCESS HEAT-CAPACITY IN A MOLECULAR GLASS - AN ASSESSMENT BASED ON CALORIMETRIC AND NEUTRON-SCATTERING DATA

The constant-pressure heat capacity C(p) for an organic glass (methanol) as well as for its polycrystalline reference state, have been measured by adiabatic calorimetry. The data are then analysed using estimates for the constant-volume contribution obtained from results of lattice dynamics calculations (for the polycrystal) and molecular dynamics calculations (for the glass). The temperature variation of C(p) is then compared with that derived from the frequency distributions measured by incoherent inelastic neutron scattering. The excess of vibrational modes which appear in the glassy state and become more pronounced at temperatures below 10 K is finally discussed and its origin is tentatively assigned.