Measurements of electron impact ionization cross sections of Mg2+ ions and a note on the classical scaling law

A crossed-beam method has been used to study the reaction Mg 2+ +e -> Mg 3+ +2e for electron energies which ranged from threshold (78 ev) to 3 kev. The cross section attained a maximum value of 1·38 × 10 -17 cm 2 at 300 ev. The results are compared with partial cross sections (for single ionization) of neon and Na + , which are the two lower members of the neon sequence. The scaling law for isoelectronic ions, which follows from Thomson's classical theory, is seen to become more accurate with increasing ionic charge for this sequence.