PNNL

Abstract

Ion/surface collision phenomena in the hyperthermal collision energy regime (1-100 eV) are reviewed, with emphasis on chemical processes associated with the impact of small organic and biological ions at functionalized self-assembled monolayer surfaces. Inelastic collisions can lead to excitation the projectile ion and can result in fragmentation, a process known as surface-induced dissociation which is useful in chemical analysis using tandem mass spectrometry.. Changes in charge can accompany ion/surface collisions and those associated with a change in polarity (positive to negative ions or vice-versa) are an attractive method for ion structural characterization and isomer differentiation. The energetics, thermochemistry and dynamics of surface-induced charge inversion of nitrobenzene and other substituted aromatics is discussed. Reactive collisions also occur between gaseous ions and surfaces and the reactions depend on the chemical nature of the collision partners. These reactions can be used for selected chemical modifications of surfaces as well as for surface analysis. Particular emphasis is given here to one ion/surface interaction, ion soft-landing, a process in which the projectile ion is landed intact at the surface, either as the corresponding neutral molecule or, interestingly but less commonly, in the form of the ion itself. The ion soft-landing experiment allows preparative mass spectrometry, for example the preparation of pure biological compounds by using the mass spectrometer as a separation device. After separation, the mass-selected ions are collected by soft-landing, at different spatial points in an array. If the experiment is done using a suitable liquid medium, at least some proteins retain their biological activity.