Direct evidence of the surface track potential

Abstract

Angular and energy distributions of fragment protons dissociated from HeH${}^{+}$ during grazing-angle scattering from a KCl $(001)$ surface are measured. The surface of KCl $(001)$ is heated at ${180}^{\ifmmode^\circ\else\textdegree\fi{}}$C and the beam current is kept lower than 1 fA to prevent macroscopic surface charging. The angular distribution of the fragment protons shows a well-defined peak similarly to the grazing-angle scattering of atomic ions. The observed peak, however, is shifted from the specular angle toward larger scattering angles. The observed angular shift for the trailing proton is larger than that for the leading proton. These results clearly indicate that the motion of the fragment protons is affected by the surface track potential induced by the partner He ion.