The Deutsch-Mark (DM) formalism was used to calculate absolute electron impact ionization cross sections for the metal oxide molecules AlO, Al2O, and WOx (x=1-3). These molecules are important in materials research and they are also found as impurities in the plasma edge of fusion reactors. We also calculated ionization cross sections for the atoms Al and W. In the case of the Al-containing compounds, we find an unexpected ordering of the maximum ionization cross section sigma (max), sigma (max)(AlO)(max)(Al)(max)(Al2O). Furthermore, the maximum ionization cross section for all four W-containing compounds W, WO, WO2, and WO3 is roughly the same with sigma (max) values in the range of 6-7 x 10(-16) cm(2). These findings can be understood by analyzing the DM calculations for these species as well as on the basis of semi-classical arguments. In addition, calculations using the semi-empirical modified additivity rule confirm the trends in the cross section ordering for, respectively, the Al-containing and W-containing compounds that was predicted by the DM formalism, at least qualitatively. (C) 2001 American Institute of Physics. References: 20
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