Charge exchange, surface-induced dissociation and reactions of doubly charged molecular ions SF 42+ upon impact on a stainless steel surface: A comparison with surface-induced dissociation of singly charged SF 4+ molecular ions

Abstract

Collisions of SF 4 2+ and SF 4 + ions with hydrocarbon-covered stainless steel surface at room temperature were investigated. The projectile ions were mass selected by a two-sector-field mass spectrometer and decelerated to incident energies of 60 to a few eV. Product ions were measured with the use of a time-of-flight spectrometer and their relative abundances determined as a function of the incident energy of the projectile ions (collision-energy-resolved mass spectra, CERMS curves). The mass spectra of product ions were dominated by fragment ions SF 3 +, SF 2 +, and SF + at incident energies below 40 eV, while sputtering of contaminant adsorbates prevailed at higher energies. The results indicate that the likely major reaction sequence responsible for the observed CERMS curves of product ions from SF 4 2+ collisions is charge exchange to form singly charged projectile ions followed by subsequent unimolecular fragmentation. In addition, chemical reactions between projectile ions and hydrocarbon adsorbates were observed leading to SF 2CH 3 +, SFCH 2 +, and SCH + ions.