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Emission cross sections for He I and He II lines between 2000 and 6000 AA have been measured for impact of Ne z+ (z=1,2,3,4) ions of 20 keV to 1 MeV on He. At a fixed impact energy it has generally been found that with increasing projectile charge the cross sections for He I decrease whereas those for He II increase and become even larger than for He I. This remarkable result is explained quantitatively by considerations of the respective quasi-molecular potential curves.
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Winter et al. (1977) studied this question.
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