Low-energy electron attachment to fullerenes and in the gas phase

Abstract

We have investigated the low-energy (0-10 eV) electron attachment on C 60 and C 70 , using an improved energy resolution close to zero incident energy (0.030-0.060 eV). We have found evidence of a zero-energy attachment process (within 0.030 eV), for both C 60 and C 70 , indicating that a s-wave capture process is present at low energy for these two molecules. For C 60 , although in contrast with symmetry arguments, and with previous free-electron attachment experiments, this result is in full agreement with the conclusions presented by several groups, using the Rydberg atom energy transfer technique to investigate the low-energy attachment in these systems. Energy positions of several resonant states, appearing between 0.5 and 5 eV in the ion yield versus electron energy spectrum, are clearly established in C 60 and C 70 , and assignments are discussed. Lifetime measurements are reported for the fullerene anions. In the incident energy range 7-11 eV the lifetime τ of C − 60 was found to vary from 500 to 45 µs, respectively, in agreement with previous measurements. The thermionic model for C − 60 detachment does not seem to describe the values obtained, and their observed variation in this energy range. The lifetime of C − 70 is longer and could not be measured precisely with our time-of-flight conditions. An estimation of τ ≈ 700 µs has been made at E i = 11 eV. Below E i = 7 eV the lifetime of C − 60 was larger than 700 µs and could not be measured precisely.

Resonance and Threshold Phenomena in Low-Energy Electron Collisions with Molecules and Clusters

“…A combined fit to these n-dependent RET data and to the free electron data of Elhamidi et al (1997) yielded c ¼ 0.1 and " ¼ 0.1-0.2 (Fabrikant and Hotop, 2001). The s-wave zero energy peak dominates the cross-section only at very low energies (below 3 meV).…”

“…They exhibit a flat dependence of the attachment rate on the principal quantum number n of the Rydberg electron at high n, indicating an s-wave attachment process. In addition, more recent beam experiments (Elhamidi et al, 1997;Vasil'ev et al, 1997;Kasperovich et al, 2001) with free electrons have found evidence for a zero-energy attachment process (within about 0.03 eV). Several mechanisms for s-wave attachment involving formation of weakly bound (Weber et al, 1996) or virtual states of C À 60 , supported by the long-range polarization interaction, have been discussed.…”

One-particle resonances in low-energy electron scattering from C60

“…Furthermore, in contrast with most other molecular systems, the measurements on C 60 found almost no resonant vibrational excitation in the gas phase. 11 Since the experimental findings suggest the occurrence of several metastable intermediates, and since the overall symmetry of C 60 is both interesting and intricate, it is useful to analyze the symmetries of the metastable states in terms of the irreducible representation ͑IR͒ of the icosahedral point group, I h , to which the C 60 molecule belongs. We have already examined the experimental angular distributions available thus far and have associated their features to our com-puted elastic differential cross sections over a broad range of collision energies.…”

Neutral C60 effusive source for atomic collisions with fullerene

“…The collision-induced electron transfer technique used in this work allows us to perform the study of negative fragmentation of the fullerene anion, which cannot be observed through electron attachment techniques. 5 …”