Ground and Excited States of Singlet, Cation Doublet, and Anion Doublet States of o-Benzoquinone:  A Theoretical Study

Abstract

The singlet excited states and doublet ionized/electron-attached states of o-benzoquinone (o-BQ) were studied by the symmetry adapted cluster (SAC)/ SAC-configuration interaction (SAC-CI) method, and the corresponding spectral bands were assigned. The calculated transition energies reasonably reproduced the experimental spectra with the mean error of about 0.2 eV, except for the 1 1 A 1 states, whose disagreement may be attributed to involvement of the shoulder peak of this state in the intense peak at approximately 6.2 eV. For the singlet states, the lowest four excited states were assigned to n, and π + -π + * ( 1 A 1 ) in order of increasing energy, and the intense band at approximately 6.2 eV in the experimental spectra was assigned to the 1 B 2 state in our calculations. For the cation doublet states, the lowest four states were assigned to n + ( 2 A 1 ), π -( 2 A 2 ), n -( 2 B 2 ), and π + ( 2 B 1 ) in order of increasing energy. Shake-up ionized states appeared in the energy region higher than 16 eV. For the anion doublet states, the ground state was 2 B 1 , and five valence excited states were calculated within 4.0 eV above the anion ground state. The adiabatic electron affinity was calculated to be 1.63 eV, which is in very good agreement with the corresponding experimental value (1.62 eV). The use of Koopmans' theorem does not reproduce this energy order for either the singlet or the doublet states. We showed that, as in the case of p-BQ (J. Phys. Chem. A 2002, 106, 3838), electron correlation is essential in the description of the excited states of o-BQ.

Theoretical study of valance photoelectron spectra of hypoxanthine, xanthine, and caffeine using direct symmetry‐adapted cluster/configuration interaction methodology

“…The other two p-type molecular orbitals are occupied by the lone pairs of the NH groups in the molecule. Based on the above explanations, the molecular orbitals (35,34,32,29,28,24) and (35,34,33,29,28,24) in Table 1 and Supporting Information Table S4 can be considered as the occupied p molecular orbitals. The four unoccupied p-type …”

Projected CAP/SAC‐CI method with smooth Voronoi potential for calculating resonance states

“…In particular, the SAC‐CI expansion can be pruned without significant loss of accuracy through a perturbation‐based selection procedure, and can in this way be applied to comparatively large systems. In relation to the present subject, the SAC‐CI method has been applied to bound electron‐attached states of molecules; for example, para ‐ and ortho ‐benzoquinones ( p ‐BQ, o ‐BQ), cyanobenzenes and nitrobenzenes, and so forth …”

Excitation Spectra of Cation and Anion Radicals of Several Unsaturated Hydrocarbons: Symmetry Adapted Cluster-Configuration Interaction Theoretical Study

“…SAC/SAC-CI is a powerful methodology including electron correlations and can describe not only closed-shell but also open-shell electronic states of various spin multiplicities. This theory has a long history of theoretical developments , and applications to various fields, such as fine spectroscopy, − photobiology, − and molecular engineering. − Furthermore, the SAC/SAC-CI method is readily applicable to the study of doublet-to-doublet excitation spectra: , both ground and excited states are calculated with the SAC-CI method starting from the appropriate closed-shell states of the molecule. In this study, we investigated the ground and excited states of the cation and anion doublet radicals of several unsaturated hydrocarbons: hexatriene ± , octatetraene ± , cyclopentadiene + , 1,3-cyclohexadiene + , and naphthalene ± .…”