Formation of autoionizing states of Ne in collisions with surfaces

We have measured energy spectra of electrons resulting from collisions of 0.4-0.5-keV ${\mathrm{Ne}}^{+}$ with solid targets of Mg, Al, and Si. We found only two peaks, in the electron-energy range 20—30 eV, corresponding to the autoionization of the ${\mathrm{Ne}}^{**}$ $2p^4({}_{}{}^3{}_{}{}^{}P,{}_{}{}^1{}_{}{}^{}D)3\mathrm{}{s}^2$ states. Unlike the spectra from gasphase collisions, the peak with the ${}_{}{}^3{}_{}{}^{}P$ core is the most intense. We interpret our results with a model involving reflection and excitation of the projectile in its collision with the surface. The excitation mechanism is similar to that of gas-phase collisions; new effects appear due to the continuum of electronic states in the solid.