Absolute Measurement of2SAtom Production by Dissociative Excitation of Molecular Deuterium

We have measured the cross section for production of metastable ($2S$) atoms by the process of dissociative excitation of molecular deuterium by electron impact. The measurement includes the quantitative evaluation of detection efficiency, density, and geometrical factors necessary to establish an absolute scale on a purely experimental basis. The method depends on the application of an rf field at the Lamb-shift frequency (1059 MHz) to quench the metastables at the point of excitation. The radiation induced by the applied field is isotropic so that the absolute cross section depends on a simple solid-angle correction. The cross sections at 23.8 and 39.1 eV are 2.97×${10}^{-18\mathrm{}}$ and 3.40×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$, respectively, with a probable error estimated to be ± 14%. The energy dependence of the cross section was also measured from threshold to 500 eV.