Anomalous kinetic energies of adsorbed ⁴He on active carbon fibre (ACF)

Direct measurements of the kinetic energies of He atoms adsorbed on active carbon fibre (ACF), at submonolayer coverage, are reported. The electronvolt spectrometer (eVs) of the ISIS neutron source, that utilizes the neutron Compton scattering technique, was employed. The specific adsorption area of the ACF was 3000 m² g^-1. The momentum distribution of adsorbed helium was measured at 4.6 Kand 10.2 K and theaverage kinetic energy K_s was found: 54.3±3.0K. This value is 30% higher than that estimated by assuming slit-shaped pores of dimensions ∼0.7 nm together with a nearly monolayer coverage on a graphitic type adsorber.