FREE-ELECTRON ATTACHMENT AND RYDBERG ELECTRON-TRANSFER TO NF3 MOLECULES AND CLUSTERS

Free electron attachment in the energy range 0-10 eV and Rydberg elect ron transfer RET) to NF3 molecules, NF3 clusters, and NF3/Ar clusters are studied by means of negative ion mass spectrometry. The experiment al results are compared with density functional theory (DFT) calculati ons. In the free electron experiment gasphase NF3 generates the dissoc iative attachment (DA) products F-, F-2(-), and NF2- appearing from a broad resonance around 2 eV, in agreement with an earlier beam experim ent. The most abundant fragment, F-, exhibits a small ''threshold'' si gnal at incident energies close to 0 eV. This signal increases with th e target gas temperature and is due to transitions from the neutral to the anion involving vibrationally excited states close to the interse ction between the two potential energy surfaces. From the temperature dependence of this threshold signal the activation energy for the exot hermic DA reaction e(-) + NF3 --> F- + NF2 is derived as E-a = 0.1 +/- 0.05 eV. Time-of-flight (TOF) analysis reveals that F- arises from a repulsive electronic state releasing the fragments with appreciable ki netic energy. Free electron attachment and RET to NF3 clusters produce undissociated cluster ions (NF3)(n-) including the monomer. In the ca se of free electrons they are still dominantly formed via the 2 eV res onance followed by intracluster relaxation processes. DFT calculations predict a lowering of the symmetry from C-3v to C-s on going from the neutral to the anion with one F atom substantially enlarged from the NF2 plane. The calculated (adiabatic) electron affinities are EA(NF3) = 1.71 eV and EA(NF2) = 1.18 eV. From the appearance energy in the DA experiment we derive EA(NF2) = 1.1 +/- 0.1 eV.