Formation of indium carbide cluster ions: experimental and computational study

We report the observation and structural analysis of novel indium carbide gas phase cluster ions generated by bombardment of a clean indium surface by keV C60(–) ions. Positive In(m)C(n)(+) (m = 1–21, 1 ≤ n ≤ 9) ions were ejected off the surface and analyzed mass spectrometrically. C60(–) ion beam irradiation is shown to be an efficient way of producing new kinds of gas phase carbide ions with relatively balanced stoichiometries. The rise kinetics of the ion signal (immediate jump within the beam opening time to a plateau value) indicates that the formation/ejection of the carbide ions constitute a single impact event. In3C2(+) was found to be the most abundant carbide cluster ion. Optimal geometries of the different clusters were derived via density functional theory calculations. The acetylenic/cumulenic nature of the impact emitted cluster ions is manifested by the high abundance of In2C2(+), In3C2(+), and the calculated structures for In(m)C(n)(+) (m = 3–4, n = 2–8). Odd/even intensity alternations in the In3C(n)(+) (n = 1–8) and In4C(n)(+) (n = 1–9) abundances are observed and rationalized by the calculations.