Coupled cluster linear-response formalism has been used to compute the vertical spectrum of ethylene and tetracyanoethylene (TCNE). We show that for both molecules the ππ∗ excitation 1A1g→1B1u of the experimental spectrum is not vertical nor the 0-0 transition. For TCNE this excitation is the only experimentally observed band. We have computed vertical excitations of 5.2 eV in gas phase and 5.1 eV in acetonitrile and estimated a lower bound for the 0-0 transition in the gas phase of 4.3 eV.... [Leer más...]