Collisions of Slow Ions C₃H_n⁺ and C₃D_n⁺ (n = 2–8) with Room Temperature Carbon Surfaces: Mass Spectra of Product Ions and the Ion Survival Probability

Abstract

Collisions of C3Hn+ (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.

Selected Ion Flow Tube Study of Ion–Molecule Reactions of N+(3P) and Kr+ with C3 Hydrocarbons Propane, Propene, and Propyne

“…The fragment C 3 H 5 + can be formed in exothermic processes with NH both in the ground and in the excited triplet state, the fragments C 2 H 3 + and C 2 H 4 + only with NH in the ground state. Some information on fragmentation pathways of internally excited C 3 H 7 + can be obtained from surface-induced dissociations of the projectile ion C 3 H 7 + . In surface collisions, a fraction of the incident energy is converted into the internal energy of the projectile hydrocarbon ion and this leads to its dissociation.…”

“…Some information on fragmentation pathways of internally excited C 3 H 7 þ can be obtained from surface-induced dissociations of the projectile ion C 3 H 7 þ . 21 In surface collisions, a fraction of the incident energy 22 is converted into the internal energy of the projectile hydrocarbon ion and this leads to its dissociation. This converted energy increases linearly with the incident energy and though its distribution is fairly broad (about 2 eV, full width at half-maximum 22 ) it provides some insight into fragmentation pathways and relative abundance of products as a function of increasing energy.…”

Surface-induced dissociation and chemical reactions of C2D4+ on stainless steel, carbon (HOPG), and two different diamond surfaces

“…In comparing CERMS curves in Figures 1 and 2, one has to take into consideration that the absolute survival probability of Ar ϩ ions on a hydrocarbon-covered room-temperature HOPG surface is only 0.005% [34], while that of C 2 D 4 ϩ ion is about 1% [24], i.e., 200-times larger. Assuming that the sputtering efficiency of lowenergy Ar ϩ and C 2 D 4 ϩ are comparable, the relative abundance scale in Figure 2 (relative to the Ar ϩ projectile) must be reduced 200 times to fit the relative abundance scale in Figure 1 (related to the C 2 D 4 ϩ projectile).…”

Modeling the intrusion of molecules into graphite: Origin and shape of the barriers

“…The interaction of molecular projectiles with fusion-relevant wall materials has been subject to a variety of experimental studies conducted in the last years [10–20] . Especially the groups of Hermann and of Märk conducted several mass-spectrometric experiments with respect to molecule/surface interactions [12,13,16–20] .…”

“…Especially the groups of Hermann and of Märk conducted several mass-spectrometric experiments with respect to molecule/surface interactions [12,13,16–20] . They let deuterated hydrocarbon ions interact with stainless steel [10,19] , carbon [11–15,17–20] , beryllium [18] and tungsten [16,18] . All of these surfaces are of relevance in thermo-nuclear fusion research.…”