Electron impact ionization of the hydrogen-like ions B⁴⁺, C⁵⁺, N⁶⁺and O⁷⁺

For the first time absolute cross sections for electron impact ionization of the hydrogen-like ions B 4+ , C 5+ , N 6+ and O 7+ at electron energies from below threshold up to about 6 keV have been measured using the crossed-beams technique. All measured cross sections are in very good agreement with available distorted-wave exchange calculations and the semiempirical Lotz formula. The behaviour of the classically scaled cross sections along the hydrogen isoelectronic sequence is discussed. A recently developed scaling technique allows us to predict all non-relativistic cross sections along the isoelectronic sequence on an absolute scale.