Imaging the Dynamics of the Electron Ionization of C2F6

Abstract

The dissociation of C2F6 following electron ionization at 100 eV has been studied using multimass velocity-map ion imaging and covariance-map imaging analysis. Single ionization events form parent C2F6+ cations in an ensemble of electronic states, which follow a multiplex of relaxation pathways to eventually dissociate into ionic and neutral fragment products. We observe CF3+, CF2+, CF+, C+, F+, C2F5+, C2F4+, C2F2+, and C2F+ ions, all of which can reasonably be formed from singly charged parent ions. Dissociation along the C–C bond typically forms slow-moving, internally excited products, whereas C–F bond cleavage is rapid and impulsive. Dissociation from the à state of the cation preferentially forms C2F5+ and neutral F along a purely repulsive surface. No other electronic state of the ion will form this product pair at the electron energies studied in this work, nor do we observe any crossing onto this surface from higher-lying states of the parent ion. Multiply charged dissociative pathways are also explored, and we note characteristic high kinetic energy release channels due to Coulombic repulsion between charged fragments. The most abundant ion pair we observe is (CF2+, CF+), and we also observe ion pair signals in the covariance maps associated with almost all possible C–C bond cleavage products as well as between F+ and each of CF3+, CF2+, CF+, and C+. No covariance between F+ and C2F5+ is observed, implying that any C2F5+ formed with F+ is unstable and undergoes secondary fragmentation. Dissociation of multiply charged parent ions occurs via a number of mechanisms, details of which are revealed by recoil-frame covariance-map imaging.