Published in Chem. Phys. Lett. 21, 445-447, doi:10.1016/0009-2614(73)80279-9 in 1973
G. P. Können, J. Grosser, A. Haring and A. E. de Vries
Negative surface ionisation of hyperthermal halogen atoms was studied as function of kinetic energy on thoriated tungsten and niobium wires. The transition from a thermal equilibrium process to direct reflection causes the ionisation to increase drastically above thermal energies: efficiencies up to 40% were found for 30 eV Cl atoms impinging on thoriated tungsten.