The angular distributions of ${\mathrm{Ni}}^{+}$ and ${\mathrm{Ni}}_2^{+}$ ejected from Ni(001) by bombardment with 2-keV ${\mathrm{Ar}}^{+}$ have been shown to exhibit large azimuthal anisotropies. The experimental results have been well reproduced by classical dynamical calculations of the ion impact event. For the dimers, the peak in the distribution arises from a unique ejection mechanism such that the atoms in the dimer are known to form from specific surface locations relative to the ion impact position.

• Received 25 September 1979

DOI:https://doi.org/10.1103/PhysRevLett.44.756