Sputtering yield Y _sp (left) and Γ (right), as a function of incident ion energy for surface binding energies of E_b = 1 eV (red) and E_b = 0.1 eV (blue); and, x = m_i∕m_n ≈ 0.15 (solid), ≈ 0.81 (dash), ≈ 1.5 (dot-dash) and ≈ 2.1 (dot). Typically the target species range from light H atoms to heavier Mg₂ SiO₄ molecules, to encapsulate this range the geometric mean of the potential target masses was calculated as kg). Therefore, for this constant value of m_n the range of x plotted cover ion masses m_i = 4.0026u (He) to m_i = 55.845u (Fe), covering the expected range of ionic masses in the atmosphere. The regime Γ > 1 (the sputtering regime) is signified by a grey shaded area. For comparison the energy of ions at the surface of the dust grain, E_sf (Fig. 3), for T_e = 1 eV and T_e = 10 eV when f_e = 1 (the degree of ionisation, f_e = n_e ∕(n_n + n_e)), are over-plotted (grey-solid).