PNNL

Abstract

The doublet and quartet anionic states of TCNQ have been studied at the configuration interaction (CI/PM3)level. Our results support an experimental claim from the Brauman group that not only the ground anionic state but also some excited states of TCNQ$^-$ are electronically stable. The core excited $1^{2}B_{3u}$ state is separated from the ground $^{2}B_{2g}$ anionic state by only 1.2 eV at the CI/PM3 level.Two externally excited $^{2}A_{u}$ and $2^{2}B_{3u}$ anionic states are separated by ca. 2.3 eV from the ground $^{2}B_{2g}$ state and are close in energy to the ground electronic state of the neutral TCNQ. In addition, two quartet anionic states $^4B_{2g}$ and $^4B_{1g}$ are found to be electronically stable with respect to the lowest triplet $^3B_{1u}$ state of the neutral. All these anionic states have minima at $D_{2h}$ geometries. Our results suggest that the $1^{2}B_{3u}$ $\leftarrow$ $^{2}B_{2g}$ and $2^{2}B_{3u}$ $\leftarrow$ $^{2}B_{2g}$ transitions contribute to the electronic absorption and electron photodetachment spectra of TCNQ$^-$. This conclusion is based on calculated values of electronic transition energies, oscillator strengths, and excess electron binding energies.