Jahn-Teller instability in C6H6+ and C6H6- revisited

TL;DR

This study models the Jahn-Teller effect in benzene cation and anion using a DFT-derived Hamiltonian, predicting vibrational frequency shifts and providing new insights into experimental data.

Contribution

It introduces a model Hamiltonian including JT coupling derived from DFT, offering a detailed analysis of vibrational spectra in benzene ions.

Findings

JT energy lowering of 970 cm^{-1} consistent with previous calculations

Predicted vibrational frequency shifts in benzene cation and anion

Reinterpreted existing experimental data on vibrational spectra

Abstract

The benzene cation (C6H6+) has a doublet (e_{1g}) ground state in hexagonal ring (D_{6h}) geometry. Therefore a Jahn-Teller (JT) distortion will lower the energy. The present theoretical study yields a model Huckel-type Hamiltonian that includes the JT coupling of the e_{1g} electronic ground state with the two e_{2g} vibrational modes: in-plane ring-bending and C-C bond-stretching. We obtain the JT couplings from density functional theory (DFT), which gives a JT energy lowering of 970 cm^{-1} in agreement with previous quantum chemistry calculations. We find a non-adiabatic solution for vibrational spectra and predict frequencies shifts of both the benzene cation and anion, and give a reinterpretation of the available experimental data.