Ionization-excitation of helium by high-resolution (e, 2e) spectroscopy and 4-body distorted-wave calculations

摘要

We present experimental and theoretical results for electron-impact-induced ionization and excitation of helium atoms. Using a high-sensitivity and high-resolution (e, 2e) spectrometer, we measured the differential cross sections of ionization-excitation of He to the n = 1?5 states of He+ at an impact energy of 600 eV. The experimental results are compared with 4-body distorted wave (4DW) calculations and first Born approximation (FBA) calculations. It was found that 4DW can well describe the shapes of the cross sections of the ionization with a simultaneous excitation. The cross-section ratios of excited states n = 2?5 to the ground state n = 1 were underestimated by FBA and 4DW calculations, indicating the need for further improvement of the theoretical methods.