Measurements of Lyman Alpha Radiation from Collisions, 100 EV to 4000EV, of Negative Hydrogen Ions on Various Target Gases and Positive Hydrogen Ions on Xenon

This study reports measurements of cross sections for the production of Lyman alpha radiation from processes in which an ion is incident on a neutral target gas. Two kinds of processes were measured: the stripping of the extra electron from a negative hydro- gen ion leaving an excited neutral and the capture of an electron by a proton also leaving an excited neutral. In each case, radiation from the 2p state of the neutral hydrogen was detected. The projectile struck the static gas target with a kinetic energy between 100 and 4000 electron volts. The measurements used the ultraviolet absorption properties of molecular oxygen to isolate the Lyman alpha line. Cross sections for emission of Lyman alpha perpendicular to the incident beam were determined. The targets used in the stripping experiments were the atomic gases: helium, neon, argon, krypton and xenon, and the molecular gases: hydrogen, nitrogen and methane. The cross sections are rela- tively flat over the energy range investigated. All are slightly below 10('-16) cm('2) at 1000 eV. Only with the neon target does the cross section fall below 2 x 10('0-17) cm('2) at 100 electron volts. While the data appear to support the modeling of stripping with excitation as a two step process, this modeling may not be valid for excitation above 2p. Only a xenon target was used in the capture experiments. Careful measurements did not substantiate an earlier report of unusual structure('1) in this cross section. ('1)P. J. Martin, Ph.D. Dissertation, Univ. of Nebraska, 1975.