Electron attachment to gas phase perfluorophenylisocyanate (C(6)F(5)NCO) and perfluorophenyloacetonitrile (C(6)F(5)CH(2)CN) 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 C(6)F(5)-X bond (X = NCO, CH(2)CN) with the excess electron finally localised on either of the two fragments. The most intense fragment ion from C(6)F(5)CH(2)CN (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 (C(6)F(5)-X) leading to the complementary DEA reactions C(6)F(5) + X(-) and C(6)F(5)(-) + X. From both condensed molecules we observe desorption of F(-) and CN(-) and, additionally, O(-) from C(6)F(5)NCO. 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.