Collisions of the Second Kind Between Magnesium and Neon

The relative intensities of a group of lines in the spectrum of Mg II as excited by a low voltage arc in a mixture of magnesium vapor and neon have been measured at various pressures of neon. Marked effects due to collisions of the second kind between magnesium atoms and neon ions and metastable atoms are found. The ratio of intensities at 2.0 and at 0.017 mm of neon was taken as a measure of the enhancement or the relative collision cross section for the excitation of the initial level. The results show a decrease of cross section with increase of energy-discrepancy, a finite cross section for exact resonance, and a definite dependence on the $L$ value of the term excited by the collision. Approximate calculation places the cross section at about ${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^2$ for collisions between neon ions and magnesium atoms.