Surface-induced dissociations and reactions of acetonitrile monomer, dimer and trimer ions

摘要

Dissociations and reactions induced by impact of acetonitrile monomer ions (CH_3CN~+, CD_3CN~+) dimer ions [(CH_3CN)_2~+, (CD_3CN)_2~+] and trimer ions [(CD_3CN)_3~+] on a hydrocarbon-covered stainless-steel surface were investigated over the projectile energy range of 3-70 eV. Both simple dissociations of the projectile ion and chemical reactions of H-atom transfer from the surface material (followed by dissociations of the protonated projectile ion formed) were observed for the monomer ions. Results obtained for the dimer ions (CD_3CN)_2~+ indicate the formation of the protonated acetonitrile ions via surface-induced reactions in two ways: (i) an intracluster ion-molecule reaction followed by dissociation to form CD_3CND~+, and (b) a hydrogen pick-up reaction from the surface material during the interaction of the dimer ion with the surface leading to CD_3CNH~+. A simple model based on the Brauman double-well potential-suggested earlier to explain the occurrence of analogous reactions in acetone cluster ion/surface interactions-accounts well for the formation of both product ions. Moreover, in adition to these protonated species, considerable amounts of nondissociated dimer ions were observed after acetonitrile dimer cation/surface collisions with energies up to 25 eV. Similarly, both trimer ions (up to 20eV) and dimer ions (up to 30 eV) were observed in acetonitrile trimer cation/surface interactions. This indicates that unimolecular dissociation kinetics governs the product formation for these cluster ion/surface interactions.