[Paper Review] Simple method for determining binding energies of fullerene negative ions

Z. Felfli, A. Z. Msezane|arXiv (Cornell University)|Feb 28, 2017

Electron and X-Ray Spectroscopy Techniques1 references3 citations

TL;DR

This paper presents a novel Regge-pole methodology using a robust potential incorporating core polarization to calculate electron scattering cross sections for fullerenes, successfully predicting the binding energies of fullerene negative ions by matching sharp resonances in total cross sections to measured electron affinities. The method achieves excellent agreement with experimental data for C60 through C92, providing the first theoretical TCSs for several fullerenes and enabling accurate extraction of electron affinities for those with no prior measurements.

ABSTRACT

A robust potential wherein is embedded the crucial core polarization interaction is used in the Regge Pole methodology to calculate low energy electron elastic scattering total cross section (TCS) for the C60 fullerene in the electron impact energy range 0.02 through 10.0 eV. The energy position of the characteristic dramatically sharp resonance appearing at the second Ramsauer Townsend (RT) minimum of the TCS representing stable C60 fullerene negative ion formation agrees excellently with the measured electron affinity (EA) of C60 [Huang et al 2014 J. Chem. Phys. 140 224315]. The benchmarked potential and the Regge-pole method are then used to calculate electron elastic scattering TCSs for selected fullerenes, from C54 through C240. The TCSs are found to be characterized generally by RT minima, shape resonances (SRs) and dramatically sharp resonances representing long lived ground state fullerene negative ion formation. For the TCSs of C70, C76, C78, and C84 the agreement between the energy positions of the very sharp resonances, corresponding to the binding energies (BEs) of the resultant fullerene negative ions, and the measured EAs is outstanding. Additionally, we extract the BEs of the resultant fullerene negative ions from our calculated TCSs of the C86, C90 and C92 fullerenes with estimated EAs larger than 3.0 eV by the experiment [Boltalina et al, 1993 Rapid Commun. Mass Spectrom. 7 1009] as well as of other fullerenes, including C180 and C240. Most of the TCSs presented in this paper are the first and only. Our novel approach is general and should be applicable to other fullerenes as well and complex heavy atoms, such as the lanthanide atoms. We conclude with a remark on the catalytic properties of the fullerenes through their negative ions.

Motivation & Objective

• To develop a general and accurate method for determining binding energies of fullerene negative ions.
• To address the lack of theoretical predictions for electron scattering cross sections (TCS) of larger fullerenes beyond C60.
• To extract binding energies for fullerenes with experimentally measured electron affinities greater than 3.0 eV, such as C86, C90, and C92.
• To extend the method to complex systems like C180 and C240, where no prior TCS data exist.
• To explore the catalytic implications of fullerene negative ions through their electronic structure.

Proposed method

• The Regge-pole methodology is employed to calculate low-energy electron elastic scattering total cross sections (TCS) for fullerenes from C54 to C240.
• A robust potential incorporating core polarization interactions is used to model electron-fullerene scattering dynamics.
• The energy position of the second Ramsauer-Townsend (RT) minimum in the TCS is identified as corresponding to the formation of stable C60⁻ negative ions.
• Sharp resonances in the TCS are interpreted as signatures of long-lived ground state fullerene negative ion states.
• The method is benchmarked against the measured electron affinity of C60, showing excellent agreement.
• Binding energies are extracted from the resonance energy positions in the calculated TCSs for fullerenes including C86, C90, C92, C180, and C240.

Experimental results

Research questions

• RQ1 Can a single theoretical framework accurately predict the binding energies of fullerene negative ions across a wide range of fullerenes?
• RQ2 How well does the Regge-pole method with a core-polarization-inclusive potential reproduce experimental electron affinities for fullerenes?
• RQ3 What is the relationship between the energy position of sharp resonances in electron scattering TCSs and the actual binding energy of the resulting negative ion?
• RQ4 Can this method reliably predict binding energies for fullerenes with no prior experimental electron affinity measurements?
• RQ5 To what extent can this approach be generalized to other complex heavy systems, such as lanthanide atoms?

Key findings

• The energy position of the second Ramsauer-Townsend minimum in the TCS for C60 matches the measured electron affinity of 2.65 eV with excellent agreement.
• For C70, C76, C78, and C84, the sharp resonance positions in the calculated TCSs align exceptionally well with their experimentally measured electron affinities.
• The method successfully extracts binding energies for C86, C90, and C92 fullerenes, which have electron affinities above 3.0 eV, based on theoretical TCSs.
• The calculated TCSs for C180 and C240 are the first of their kind, providing a foundation for future experimental validation.
• The approach demonstrates high accuracy and generalizability, suggesting applicability to other fullerenes and complex heavy atoms like lanthanides.
• The study concludes that fullerene negative ions may possess catalytic properties due to their stable anionic states and electron affinity characteristics.