Electron attachment to the perfluoroalkanes n-CNF2N+2 (N=1–6) and i-C4F1 a)

Abstract

Parent and fragment negative ion formation from seven perfluoroalkanes [n-CNF2N+2 (N=1–6) and i-C4F10] under low-energy (0–10 eV) electron impact has been studied using a time-of-flight mass spectrometer. For CF4, C2E6, and C3F8 only fragment anions were observed, F− being the most abundant. For n-C4F10 a weak parent ion was observed, but again the predominant ion was F−. For i-C4F10, n-C5F12, and n-C6F14 the parent negative ions were the most abundant with relative cross sections peaking at 0.6 eV and autodetachment lifetimes from 10 to 100 μs depending on the molecular size and electron energy. In addition to the parent negative ion and the F− ion, fragment negative ions of the form CNF−2N+1, CNF−2N, CNF−2N−1 (with N=1–6) have been detected. The relative cross sections for all observed negative ions have been measured and corrected for the finite width of the electron pulse using an unfolding procedure. The positions of the dissociating negative ion states (NISs) shift to lower energies with increasing size of the molecule. Possible fragmentation mechanisms of the NISs leading to the production of the observed fragment negative ions have been suggested and discussed. From the appearance onsets of a number of fragment negative ions, various C–C and C–F bond dissociation energies, heats of formation, and electron affinities EA of certain fragments have been determined and are reported. It was found that the EA of perfluorocarbon radicals increases with increasing size of these radicals, and similar behavior is indicated also for the perfluoroalkane molecules themselves. The separation times of the dissociating fragments and the autodetachment lifetimes of the extremely short-lived (∼10−15 s) and dissociating NISs of CF4 and C2F6 were estimated. The intensity of the parent anion as a function of molecular size and geometry is discussed, and the relative intensities of the fragment negative ions are rationalized on the basis of the present work and relevant data from electron swarm studies.

Effects of Temperature on Dissociative and Nondissociative Electron Attachment

“…7 the k (<e>,T) are given along with the relative abundance of the fragment negative ions observed (inset, Fig. 7) in a beam study [17]. No parent negative ions were observed in the low pressure beam study, and this is consistent with the absence of any pressure dependence of k (<e>,T) in the swarm study.…”

“…The k (<e>,T) were independent of gas number density [15]. Inset: Relative intensity of the dissociative attachment fragment anions measured [17] in a low pressure beam study. 500 K. These measurements are shown in Fig.…”

“…15a are also compared the cross sections due to only the dissociative attachment contribution to the total cross section at 300 K (curve S) and the total (for all fragment anions) dissociative attachment cross section for C 3 F 8 measured in a single collision electron beam study [17]; the latter was normalized to the peak value of the former. It is seen that the peak positions of the two cross section functions agree well and that both lie at a higher energy than the total unfolded cross section o (e,300 K).…”

Electron attachment mass spectrometry as a diagnostics for electronegative gases and plasmas

“…Moreover, at 3 eV another resonance is present, which is especially clearly visible at 10 W. This peak has been ascribed to plasma produced C 3 F 8 , based on its attachment cross section provided in Ref. 12; ͑b͒ the C 2 F 6 partial pressure, obtained by calibrating the data with the cross section from Fig. 4.…”

Effect of Silane Coupling Agent Chemistry on Electrical Breakdown Across Hybrid Organic–Inorganic Insulating Films

“…43 Additionally, the highly electronegative nature of fluorine and the ionic C-F bond may cause scattering of ballistic electrons [44][45] and act as electronic traps. 10 Additionally, molecular dipole moments have been correlated directly with mean electron scattering cross-sections.…”