Atom - cluster collisions

Table of contents

1. 1.  "Transparency" in atom - metal cluster collisions
   2. "Stopping power" of H+ and Ar+ in collisions with C60

 "Transparency" in atom - metal cluster collisions

The energy loss ΔE in Na₉⁺ + Na collisions as a function of the (center of mass) bombarding energy E_cm clearly shows a minimum at intermediate E_cm around 1 keV. Obviously, the corresponding impact velocity is too large to excite vibrations and still too small to excite electrons and, thus, the atom penetrates the cluster nearly freely ("Transparency") [2].

Total kinetic energy loss of relative motion ΔE in central Na₉⁺ + Na collisions for a fixed collision geometry (see inset) as a function of the center-of-mass impact energy E_cm calculated with NA-QMD (solid line) and QMD (dotted line). Vibrational and electronic contributions to ΔE are distinguished by gray and light-gray shaded areas, respectively (Figure taken from [2]).

Total fragmentation cross section σ_frag as a function of E_cm calculated with NA-QMD (solid line). The circles are experimental data (Figure taken from [2]).

 

"Stopping power" of H⁺ and Ar⁺ in collisions with C₆₀

In the movies the (totally different) collision mechanisms are visualized:

• (a) H⁺ with v=0.05 a.u. is reflected (backward scattering).
• (b) Ar⁺ with v=0.05 a.u., however, destroys the cage completely due to pure vibrational excitations ("nuclear stopping power").
• (c) Ar⁺ with v=0.45 a.u. penetrates the cage freely without any vibrational excitation, but the cage is electronically highly excited ("electronic stopping power").
  Electron-vibration coupling leads to excitation of a giant breathing mode.
  
   

• T. Kunert and R. Schmidt, Excitation and Fragmentation Mechanisms in Ion-Fullerene Collisions, Phys. Rev. Lett. 86, 5258 (2001).
• U. Saalmann and R. Schmidt, Excitation and Relaxation in Atom-Cluster Collisions, Phys. Rev. Lett. 80, 3213 (1998).