Calculated absolute cross section for the electron-impact ionisation of simple molecular ions

We report the results of the application of the semi-classical Deutsch-Mark (DM) formalism to the calculation of the absolute electron-impact ionisation cross section of the molecular ions H-2(+), N-2(+), O-2(+), CD+, CO+, CO2+, H3O+/D3O+, and CD4+ for which experimental data have been reported. Where available, we also compare our calculated cross sections with calculated cross sections using the BEB method. The level of agreement between the experimentally determined and the calculated cross section is satisfactory only in a few cases. In most cases, the calculated cross sections exceed the measured cross sections, in some cases significantly, which is not surprising in view of the experimental complications in measuring ionisation cross sections of molecular ions due to the presence of competing channels for the formation of fragment ions such as dissociative excitation versus dissociative ionisation. (C) 2002 Elsevier Science B.V. All rights reserved.