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

Abstract

Dissociations and reactions induced by impact of acetonitrile monomer ions (CH3CN+, CD3CN+), dimer ions [(CH3CN)2+, (CD3CN)2+] and trimer ions [(CD3CN)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 (CD3CN)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 CD3CND+, and (b) a hydrogen pick-up reaction from the surface material during the interaction of the dimer ion with the surface leading to CD3CNH+. 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 20 eV) 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.