Atom and molecule emission caused by ion impact into a frozen oxygen target: Role of rovibrational excitation

Translational energy distributions of particles sputtered by 750 eV Ne+ ion impact into a cryogenic O2 target are studied using molecular-dynamics simulation. When comparing the energy distribution of emitted molecules to a Thompson distribution, good agreement can only be found for energies E with U<E<D, where U is the surface binding and D the dissociation energy of oxygen molecules. At smaller energies, a strong spike contribution enhances the spectrum. At higher energies (≳0.5 eV), simulation shows a deficiency in sputtered molecules compared to the Thompson distribution; we show that this can be traced back to the decay of highly rovibrationally excited molecules after emission. Around 2% of the sputtered particles consist of radicals (atomic O). These originate from direct projectile-molecule collisions; they are emitted early in the collision cascade and feature a strong high-energy contribution