Collisions of Slow Ions C 3 H n + and C 3 D n + ( n = 2–8) with Room Temperature Carbon Surfaces: Mass Spectra of Product Ions and the Ion Survival Probability

Collisions of C₃H _n ⁺ (n = 2–8) ions and some of their per-deuterated analogs with room temperature carbon (HOPG) surfaces (hydrocarbon-covered) were investigated over the incident energy range 13–45 eV in beam scattering experiments. The mass spectra of product ions were measured and main fragmentation paths of the incident projectile ions, energized in the surface collision, were determined. The extent of fragmentation increased with increasing incident energy. Mass spectra of even-electron ions C₃H₇⁺ and C₃H₅+ showed only fragmentations, mass spectra of radical cations C₃H₈^•+ and C₃H₆^•+ showed both simple fragmentations of the projectile ion and formation of products of its surface chemical reaction (H-atom transfer between the projectile ion and hydrocarbons on the surface). No carbon-chain build-up reaction (formation of C4 hydrocarbons) was detected. The survival probability of the incident ions, S_a, was usually found to be about 1–2% for the radical cation projectile ions C₃H₈^•+, C₃H₆^•+, C₃H₄^•+ and C₃H₂^•+ and several percent up to about 20% for the even-electron projectile ions C₃H₇⁺, C₃H₅⁺, C₃H₃⁺. A plot of S_a values of C1, C2, C3, some C7 hydrocarbon ions, Ar⁺ and CO₂⁺ on hydrocarbon-covered carbon surfaces as a function of the ionization energies (IE) of the projectile species showed a drop from about 10% to about 1% and less at IE 8.5–9.5 eV and further decrease with increasing IE. A strong correlation was found between log S_a and IE, a linear decrease over the entire range of IE investigated (7–16 eV), described by log S_a = (3.9 ± 0.5) – (0.39 ± 0.04) IE.