Spin conservation during chemi-ionization and surface-electron ejection byHe(2S3)

Abstract

The conservation of spin angular momentum during inelastic collisions of spin-oriented metastable $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ atoms with contaminated surfaces and a variety of gaseous targets, including Ar, ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, CO, C${\mathrm{O}}_2$, and ${\mathrm{N}}_2$O, has been investigated. The metastables are contained in a flowing helium afterglow and are oriented by optical pumping. The electrons produced during subsequent chemi-ionization and surface-ejection reactions are extracted and spin analyzed by Mott scattering. Spin angular momentum is found to be fully conserved for all the reactions studied, with the possible exception of the chemi-ionization of CO. The experimental results are discussed in the light of existing theories and models for chemi-ionization. The results also suggest that secondary electron ejection from chemically cleaned surfaces occurs through chemi-ionization of adsorbed species.