A mechanism for ageing in a deeply supercooled molecular glass

Measurements of the decay of electric fields, formed spontaneously within vapour-deposited films of cis-methyl formate, provide the first direct measurements of the energy barrier to secondary relaxation mechanisms in a molecular glass, at temperatures far below the glass transition temperature. The mechanism of low temperature relaxation is shown to be through hindered molecular rotation. Magnetically-polarised neutron scattering experiments exclude diffusion, which is demonstrated to take place only close to the glass transition temperature.