Reactions in gas phase and condensed phase C6F5X (X = NCO, CH2CN) triggered by low energy electrons

Abstract

Electron attachment to gas phase perfluorophenylisocyanate (C₆F₅NCO) and perfluorophenyloacetonitrile (C₆F₅CH₂CN) generates metastable parent anions within a very narrow resonance close to zero energy. At higher energies (2–7 eV), dissociative electron attachment (DEA) resonances are present, associated with the rupture of the C₆F₅–X bond (X = NCO, CH₂CN) with the excess electron finally localised on either of the two fragments. The most intense fragment ion from C₆F₅CH₂CN (M) is (M − HF)⁻, which arises from the loss of a neutral HF from the transient anion and requires the concerted cleavage of two bonds and formation of a new molecule (HF). Most remarkably, this rather complex DEA reaction is by about two orders of magnitude more intense than the single bond cleavages (C₆F₅–X) leading to the complementary DEA reactions C₆F₅ + X⁻ and C₆F₅⁻ + X. From both condensed molecules we observe desorption of F⁻ and CN⁻ and, additionally, O⁻ from C₆F₅NCO. The desorption yields also show a resonant behaviour with the peak maxima in the range 8–12 eV, i.e., near or above the ionization energy, indicating that in electron stimulated desorption (ESD) highly excited resonances are involved. Ab initio calculations are performed in order to get information on the shape and energy of the molecular orbitals involved in low energy (<2 eV) electron attachment.