A measurement of the cross section for ionisation of Cr+ by electron impact

The absolute cross section for the ionisation process Cr++e → Cr2++2e has been measured at electron energies ranging from the ionisation threshold to 1000 eV using the crossed electron-ion-beams technique. The cross section rises from a threshold of 13.5 eV to a maximum of 1.22 x 1016 cm2 at approximately 65 eV. The total error in the cross section is estimated to be less than +-4.6% at a 90% confidence level for energies above 16 eV. The results show that the Cr+ beam contains mainly ions in the 6S ground state and 6D mestastable state but also some higher metastable-state ions. The experimental data are compared with results calculated using the scale Born Approximation of McGuire [1977, Phys. Rev. A, 16, 73-9]. (author)