The Franck–Condon effect in the lowest energy [formula omitted] state of tetracyanoquinodimethane anion. The resonance Raman studies in terms of density functional theory

Abstract

The absorption and resonance Raman (RR) excitation profiles (EPs) of ν 2=2192 cm −1, ν 4=1389 cm −1, ν 5=1195 cm −1 and ν 9=336 cm −1 fundamentals in the excitation region corresponding to 1 2 B 1g →1 2 B 2u transition in the tetracyanoquinodimethane (TCNQ) anion are studied in terms of vibronic model based on the Franck–Condon (FC) effect. The studies are carried out in terms of the local spin density Vosco–Wilk–Nusair (VWN) and the nonlocal spin density Becke–Perdew (BP) density functional theory (DFT) scheme applied with the double numerical functions augmented by polarization functions (DNP). The BP/DNP method leads to FC parameters, which only roughly correspond to those required to reconstruct the absorption and RR spectra. On the other hand, the VWN method is shown to offer reasonable, even if approximate, scheme to study the RR spectra of the TCNQ anion under resonance with the 1 2 B 1g →1 2 B 2u transition.