DISSOCIATIVE ELECTRON-ATTACHMENT TO GAS-PHASE AND CONDENSED-PHASE CF3CL - ANION DESORPTION AND TRAPPING

The interaction of electrons in the energy range from near zero to 10 eV with CF3Cl physisorbed on a Kr surface is studied and compared with previous gas-phase experiments on isolated molecules and CF3Cl cluste rs. In the gas phase CF3Cl shows resonances in the dissociative attach ment (DA) cross section at 1.4 eV, near 4-5 eV, and at 9 eV with the 1 .4 eV feature assigned as a single particle resonance with a strong C- Cl repulsive nature. From adsorbed CF3Cl, we observe desorption of Cl- and F- with resonances in the cross section which can be correlated t o the gas-phase DA features. Despite its antibonding nature, Cl- desor ption via the single particle resonance is very weak, indicating that direct desorption processes do not occur; i.e., orientations of the mo lecule with the C-Cl axis pointing away from the surface can be exclud ed, and desorption is always preceded by postdissociation interactions . Charge trapping is virtually restricted to the low-energy resonance. Its maximum is at 0.8 eV and reflects the energy shift of the transie nt ion due to solvation. The absolute trapping cross section is 43 x 1 0(-18) cm(2), exceeding the gas-phase DA value by about 1 order of mag nitude. The behavior of the low-energy resonance is described in terms of one-dimensional potential energy curves previously used to model t emperature effects in DA to gas-phase CF3Cl, with the anionic curve sh ifted by the solvation energy. It is shown that autodetachment, which is by far the dominant decay channel in the gas phase, is substantiall y suppressed in the condensed phase.