Absolute cross-section measurements for electron impact ionisation of Li-like N4+, O5+and Ne7+ions

Measured cross sections for single ionisation of Li-like N 4+ , O 5+ and Ne 7+ by electron impact are reported for energies from threshold to 2500 eV. The animated crossed beams method has been employed. In addition to direct ionisation, the 1s 2 2s to 1s2l2l' excitation followed by autoionisation is shown to give a significant contribution to the total cross section, and its magnitude has been estimated for all three ions. Comparisons are made with other experimental results and different theoretical predictions. Cross sections for N 4+ and O 5+ are in a good agreement with previous results and the first result on Ne 7+ ionisation is well reproduced by the Coulomb-Born calculations.