[Paper Review] Doubly-charged Negative Ion of C60 Molecule

A. Z. Msezane, A. S. Baltenkov|arXiv (Cornell University)|Jan 15, 2016

Atomic and Molecular Physics1 references3 citations

TL;DR

This study investigates the existence and properties of the doubly-charged negative ion (C60^2−) using variational methods within Dirac- and Lorentz-bubble potential models. It demonstrates a stable bound state with a total energy below zero and estimates the second electron affinity of C60 at approximately 1 eV, while photodetachment cross sections show distinct threshold behaviors, including exponentially small cross sections for the first detachment process and power-law growth for the second.

ABSTRACT

Within the Dirac- and Lorentz-bubble potential models an electronic structure of the doubly-charged negative ion has been studied by a variational method. It is shown that even in the first approximation of this method when a trial wave function of the two electrons is represented as a product of one-electron functions the total energy of the system is negative, a manifestation of the existence of a stable state of the doubly-charged negative ion in these models. The second electron affinity of C60 according to estimation is about 1 eV. The photodetachment cross sections of this ion have been calculated as well. Near threshold behavior of cross section is found to exhibit peculiar and interesting behavior. The first cross section accompanied by the transformation of the doubly-charged negative ion into a singly-charged one is exponentially small near the process threshold. The second cross section corresponds to the photodetachment of a singly-charged ion; it increases at the threshold as a power function of the kinetic energy of the photoelectron. These cross sections are of the same order as the photodetachment cross sections of atomic ions with the same electron affinity. AMS (MOS) Subject Classification. 70G75, 81V10, 81V55

Motivation & Objective

• To determine the electronic structure and stability of the doubly-charged negative ion of C60.
• To estimate the second electron affinity of C60 using quantum mechanical models.
• To analyze the photodetachment cross sections of C60^2− and understand their threshold behavior.
• To compare the photodetachment dynamics of C60^2− with those of atomic ions of similar electron affinity.

Proposed method

• Employed a variational method with a trial wave function constructed as a product of one-electron functions.
• Used Dirac- and Lorentz-bubble potential models to describe electron correlation and electron-nucleus interactions in C60^2−.
• Calculated total energy of the system to assess the stability of the doubly-charged negative ion.
• Computed photodetachment cross sections for both detachment steps: C60^2− → C60^− and C60^− → C60.
• Analyzed the threshold behavior of the cross sections, distinguishing between exponential suppression and power-law divergence.
• Validated results by comparing with known photodetachment cross sections of atomic ions with similar electron affinities.

Experimental results

Research questions

• RQ1 Does the doubly-charged negative ion of C60 (C60^2−) support a stable bound state?
• RQ2 What is the estimated value of the second electron affinity of C60?
• RQ3 How do the photodetachment cross sections of C60^2− behave near the threshold energy?
• RQ4 What is the nature of the threshold dependence for the first and second photodetachment processes?
• RQ5 How do the photodetachment cross sections of C60^2− compare quantitatively with those of atomic ions of comparable electron affinity?

Key findings

• The total energy of the C60^2− ion is negative in the first approximation, indicating the existence of a stable bound state within the model.
• The second electron affinity of C60 is estimated to be approximately 1 eV based on the variational energy calculation.
• The photodetachment cross section for the first detachment (C60^2− → C60^−) exhibits exponentially small behavior near threshold.
• The photodetachment cross section for the second detachment (C60^− → C60) increases as a power function of the photoelectron's kinetic energy near threshold.
• The magnitudes of the photodetachment cross sections are comparable to those observed in atomic ions with similar electron affinities.
• The model predicts distinct threshold behaviors, highlighting the importance of electron correlation and potential structure in fullerenes.