Deexcitation of helium 23S, 21

Electron Spectroscopy Using Metastable Atoms as Probes for Solid Surfaces

“…Recently MAES using spin-polarized metastable atoms has been developed by Dunning and his collaborators, who named the method SPMDS (spin-polarized metastable-atom deexcitation spectroscopy) . Their apparatus is shown in Figure …”

The dynamics of He+ ion neutralization at a xenon film: Energy- and spin-resolved studies

“…The polarization P e $ 0.27 observed at low He + ion energies is a factor of two smaller than the polarization of the low-energy feature observed in studies of the deexcitation of polarized, thermal-energy He(2 3 S) metastable atoms at a thick ($7 ML) xenon film [10]. This low-energy peak was attributed to the neutralization of (polarized) He + ions produced by resonance ionization of incident He(2 3 S) atoms.…”

“…This can be attributed to the fact that the He + ions are formed with thermal energies leading to a very small component of ion energy perpendicular to the surface. (No similar low-energy feature was observed at an argon film [10].) The majority of the incident atoms, however, are deexcited by Auger deexcitation, also referred to as surface Penning ionization, which results in the production of highly-polarized (P e $ 1) electrons with energies in the range 7-10 eV.…”

“…If these contribute significantly to the low-energy feature they will increase the average polarization above that characteristic of simple He + Auger neutralization. Although in earlier studies with He(2 3 S) metastable atoms He + ion neutralization was discussed in terms of an Auger process involving two neighboring xenon atoms [10], the present work suggests that a band structure picture involving delocalized electrons is more appropriate.…”

“…Studies involving a thick CO 2 film have shown that ion impact leads to efficient electron ejection through formation of an autoionizing complex made up of the incident ion and two neighboring CO 2 molecules in which a significant portion of the kinetic energy of the incident ion is converted to potential energy [9]. Earlier studies of electron ejection from xenon films by incident He(2 3 S), He(2 1 S) and He(2 3 P) atoms revealed a low-energy feature in the ejected electron energy distribution that was attributed to Auger neutralization of He + ions produced by resonance ionization of incident atoms [10]. It was postulated that this resulted from a neutralization process that involved a pair of xenon atoms in which the He + ion was neutralized by the 5p electron from one xenon atom tunneling into the 1s core hole, the energy liberated being used to eject a 5p electron from a neighboring atom.…”