Triple-differential cross sections for ionization of hydrogen atoms by electrons have been calculated both for small-as well as large-momentum-transfer cases at intermediate (5I0 -20I0) and high { & 20I0) energies (I0 being the ionization potential) following a method which uses a final-channel three-particle wave function determined by one of the authors. This wave function resulted from an analysis of the three-particle wave equation in momentum space and is correct to the first order in the interaction potentials. Incidentally, it is also the first-order Faddeev wave function. The wave function has been suitably normalized before it is used. The computed results are generally good. The small-momentumtransfer results are in nice agreement with the experimental data except for a certain angular region which includes the recoil peak. The domain over which the present results agree in trend with the experimental measurements is somewhat larger than that for the distorted-wave-Born-approximation calculation. Large-momentum-transfer results are also in qualitative agreement with experiments. There are indications that quantitatively the present results may be better there. Total-ionization cross-section results are also in excellent agreement with experiment above 200-eV energy. These facts together with the simplicity of the calculation establish that the present method has certain advantages over other existing methods. The present calculation may be the starting point for a more elaborate calculation which will take into account more accurately the correlation and higher-order effects in the final-channel three-particle wave function.PACS number(s): 34.80.0p

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Abstract. The multiple scattering approach of Das and Seal, which was applied earlier to calculate the triple differential cross section for the ionization of atomic hydrogen by electrons is now used to calculate the double and the single differential cross sections for the same system. The range of the incident electron energy is taken to be 100-250 eV. The present results are compared with the measured results of Shyn and with the available distorted wave Born approximation results.

A new theory, recently suggested by one of the authors, is tested here in case of ionization of hydrogen atoms by electrons at intermediate energies for large momentum transfers. The present results give good description of the available experimental data and in some respects are better than those of other theories.

The triple differential cross section for electron impact ionisation of helium atoms has been calculated in the coplanar asymmetric geometry following the multiple scattering approach of Das. The method has already been successfully employed to describe the electron impact ionisation problem for the hydrogen atom. Here the impact energy of the incident electron is taken to be 150 and 250 eV in an intermediate energy range where there are still some discrepancies between theory and experiment. Present results are compared with the available experimental data and with two of the most recent calculations in some cases, and are found to be in reasonable accord with experiment, particularly in the binary peak region. The present calculation for 250 e V incident energy reproduces the experimental results in some cases better than other theories.