Free Electron Attachment and Rydberg Electron Transfer to NF₃Molecules and Clusters

Abstract

Free electron attachment in the energy range 0−10 eV and Rydberg electron transfer (RET) to NF3 molecules, NF3 clusters, and NF3/Ar clusters are studied by means of negative ion mass spectrometry. The experimental results are compared with density functional theory (DFT) calculations. In the free electron experiment gas-phase NF3 generates the dissociative attachment (DA) products F-, F2 -, and NF2 - appearing from a broad resonance around 2 eV, in agreement with an earlier beam experiment. The most abundant fragment, F-, exhibits a small “threshold” signal at incident energies close to 0 eV. This signal increases with the target gas temperature and is due to transitions from the neutral to the anion involving vibrationally excited states close to the intersection between the two potential energy surfaces. From the temperature dependence of this threshold signal the activation energy for the exothermic 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 kinetic energy. Free electron attachment and RET to NF3 clusters produce undissociated cluster ions (NF3) n - including the monomer. In the case of free electrons they are still dominantly formed via the 2 eV resonance followed by intracluster relaxation processes. DFT calculations predict a lowering of the symmetry from C 3 v 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.

A new instrument for thermal electron attachment at high temperature: NF3 and CH3Cl attachment rate constants up to 1100 K

“…The electron-beam experiment of Ruckhaberle et al 39 with NF 3 clearly showed a zero-energy resonance for the production of F − , which grew as the NF 3 temperature was TABLE I. Electron attachment rate constants k a for NF 3 obtained with the FALP apparatus and the new HT-FALP apparatus in the present work. The experimental uncertainty is Ϯ25% except for the 300 K datum ͑Ϯ50%͒.…”

“…G3 energies for molecules needed in the calculation of reaction energetics are tabulated in Table II. G3 and experimental [39][40][41][42] electron affinities are also listed in Table II. With all data included, the activation energies determined with the FALP and HT-FALP from Arrhenius fits ͑Fig. 6͒ are 0.22 and 0.25 eV, respectively.…”

“…Ruckhaberle et al 39 described this result as incompatible with the larger activation energy of the 1995 FALP experiment, and consequently with the present 0.25Ϯ 0.05 eV. Ruckhaberle et al 39 acknowledged that there is a difference between the two experiments in that their activation energy corresponded to a nominal electron energy of 0 eV, while the FALP experiment is truly thermalized, i.e., the average electron energy follows 3kT / 2, and hence increases from 0.039 to 0.12 eV in the present work with NF 3 . Ruckhaberle et al 39 supported their low activation energy with density functional calculations on the change in NF 3 potential energy for N-F stretching motion, which yielded an activation energy of 0.2 eV, believed an overestimate.…”

Structural properties and electron transfer reactivity of NX3/NX3+ (X=H, F) coupling systems

“…In addition, the use of NF 3 can also prevent carbon contamination and create only minor crystal damage. Recently, many works have focused on the NF 3 or NF 3 K system [24][25][26]. For example, Nike and his coworkers [25] studied free electron attachment and Rydberg ET to NF 3 molecules and clusters; however, the study of NF 3 /NF 3 C coupling system has not been done.…”

“…Recently, many works have focused on the NF 3 or NF 3 K system [24][25][26]. For example, Nike and his coworkers [25] studied free electron attachment and Rydberg ET to NF 3 molecules and clusters; however, the study of NF 3 /NF 3 C coupling system has not been done. One of the goals of the present article is to theoretically study the structures, properties, and the ET reactivity of NX 3 /NX 3 C (XZH, F) systems, and to discuss the contact distance dependence of various ET kinetics parameters such as the activation energy, the coupling matrix element and the ET rate.…”