The vibronic effects in the excited 1 1E u state of (CO) 4 dianion in terms of time dependent (TD) density functional theory: The resonance and pre-resonance Raman studies

Abstract

Franck–Condon (FC) and Jahn–Teller (JT) effects in the 1 1E u state of the (CO) 4 dianion are examined in terms of time dependent density functional theory (TD DFT) at the B3LYP/6-31G+* level. The experimental absorption, pre-resonance and resonance Raman spectra associated with 1A g → 1 1E u(ππ*) transition are studied. The computations indicate considerable activities of ν 5(b 2g) = 1073 cm −1 (CC stretching) and ν 10(b 1g) = 624 cm −1 (ring bending) modes due to JT effect in the 1 1E u(ππ*). Of two totally symmetric modes of the squarate dianion only single ν 2(a 1g) = 698 cm −1 (ring breathing) vibration is shown to exhibit the sizable Franck–Condon activity in the lowest energy 1 1E u(ππ*) state of the squarate dianion.