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The preceding Comment reports some low-energy -impact spectra of helium and ethylene, obtained by a very elegant technique, which are markedly from the ones we obtained 1 other experimental conditions. It is quite important to try to the reasons for the differences observed. differences are essentially the following: (a) In impact spectra of helium obtained with 50-eV we observe pronounced peaks corresponding the 2 ³S state and to ionization whereas Simpson Mielczarek do not. (b) In our spectra of ethylene this same incident electron energy we observe two optically forbidden transitions and
Kuppermann et al. (Sun,) studied this question.