Yields of H + and He + at the energy for elastic scattering from H 2+3He + incident on Ag and Pd

Abstract

Yields, Y, of H + and He + emerging specularly with the energy for single binary elastic collisions have been measured from polycrystalline Ag and Pd surfaces bombarded with mixed monoenergetic (300 < E 0 < 2600 eV) beams of H 2 + 3He + impinging at an angle of 45° from the surface normal. The surfaces were exposed to H 2 + at a dynamic pressure of 8 × 10 −3 Pa (6 × 10 −5 Torr) during the measurements. The He + yields from Pd are slightly larger than from Ag, and the H + yields from Pd are 10 to 40 times as large as those from Ag. These results suggest that differences between Pd and Ag in the amount of hydrogen adsorbed and in the character of the hydrogen-metal bond may be responsible for the yield differences through shadowing by, and possibly the sputtering of, adsorbed hydrogen. The Y versus E 0 curves for all four systems have qualitatively the same singly peaked shape which implies that reactive and noble gas ions undergo similar neutralization processes during elastic surface collisions. The ratios of the yields from Ag and Pd do not exhibit the theoretically expected exponential dependence on collision time over the entire range studied, but at the lowest energies the ratios lead to estimates of the difference of neutralization constants which do agree with theory. The potential utility of the large difference in proton yields from Ag and Pd for studying the Ag-Pd alloy system is noted.