The Optical Excitation Function of Helium

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Abstract
With a discharge tube which has been considerably modified from the designs previously used, and with a technique specially developed to eliminate the effects of collisions of the second kind and ionization and recombination, the author has completed a study of the excitation function of helium for electrons with energies between the excitation potentials and one hundred volts. Two new features are introduced, namely, experimental conditions under which a linear dependence of intensity on either current or pressure is obtained, and an actual determination of the electron velocity distribution curve. The intensity curves, by themselves, agree fairly well with those obtained by earlier workers but, by the innovations mentioned above, it has been possible to correct these curves to obtain the true optical excitation function values. The corrected results show that each line has a maximum excitation probability either at or within a few tenths of a volt of the excitation potential, and that the probability drops off quite rapidly above this value, more rapidly for the triplet system than for the singlet.

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