Emission of the Werner Band System and Lyman-α Radiation for 0.05–6-keV Electrons in H2

Abstract

We have measured relative cross sections as a function of impact energy for the emission of Werner bands ${\text{C (2pπ\hspace{0.17em}}}^1{\Pi }_u{\text{)‐(1sσ\hspace{0.17em}}}^1{\Sigma }_g^{+})$ and Lyman‐α radiation for 0.05–6‐keV electrons on molecular hydrogen. The cross sections for the Werner bands are normalized on theoretical Born or Bethe cross sections, evaluated by means of the theoretical generalized oscillator strengths of Miller and Krauss and the theoretical optical oscillator strengths and transition probabilities of Allison and Dalgarno. By comparing the cross sections thus obtained and the relative intensity measurements, the sensitivity of our optical detection system can be determined between about 1030 and 1250 Å. It is then also possible to bring the relative cross sections for Lyman‐α radiation at 1215.7 Å on an absolute scale. The latter cross sections appear to be 1.31 times smaller than those reported by Vroom and De Heer, which data were normalized on the so‐called countable ultraviolet cross sections of Fite and Brackmann. In the latter normalization, the contribution of the Werner bands to the countable ultraviolet cross sections has been neglected.