What Can We Learn on the Above-Surface Neutralization Process from the Chemical Sputtering Yields of D, D$_{2}$ AND D$_{3}$ at Carbon Surface?

We perform molecular dynamics simulations of chemical sputtering of methane and acetylene from deuterated amorphous carbon surface, by impact of deuterium, as well as of vibrationally excited D$_{2}$ and dissociating D$_{3}$ molecules in range of 5-30 eV/D impact energies. We show that the chemical sputtering yields at the lowest impact energies are very sensitive to the vibrational state of the molecules. Our sputtering yields are compared with those obtained experimentally [L.I. Vergara et al, J. Nucl. Mat. (2006), in press] by impact of D, D and D. Analyzing possible processes of the above-surface neutralization of the impinging ions in the experiment we conclude that the leading mechanism is the charge transfer from the surface-bound deuterium atoms onto vibrationally excited states of the molecules.