Electronic structure of the benzene dimer cation

Abstract

The benzene and benzene dimer cations are studied using the equation-of-motion coupled-cluster model with single and double substitutions for ionized systems. The ten lowest electronic states of the dimer at t-shaped, sandwich, and displaced sandwich configurations are described and cataloged based on the character of the constituent fragment molecular orbitals. The character of the states, bonding patterns, and important features of the electronic spectrum are explained using qualitative dimer molecular orbital linear combination of fragment molecular orbital framework. Relaxed ground state geometries are obtained for all isomers. Calculations reveal that the lowest energy structure of the cation has a displaced sandwich structure and a binding energy of 20 kcal/ mol, while the t-shaped isomer is 6 kcal/ mol higher. The calculated electronic spectra agree well with experimental gas phase action spectra and femtosecond transient absorption in liquid benzene. Both sandwich and t-shaped structures feature intense charge resonance bands, whose location is very sensitive to the interfragment distance. Change in the electronic state ordering was observed between and u states, which correlate to the B and C bands of the monomer, suggesting a reassignment of the local excitation peaks in the gas phase experimental spectrum.

Spectroscopic signatures of proton transfer dynamics in the water dimer cation

“…Electronic states of the dimer cation can be conveniently described in terms of the dimer molecular orbitals -linear combination of fragment molecular orbitals (DMO-LCFMO) approach [29,45]. In this framework we adopt a composite notation of the form (hydrogenbond donor orbital)/(hydrogen-bond acceptor orbital) to describe the dimer molecular orbitals.…”

“…Moreover, EOM-IP-CCSD allows one to compute transition properties required for spectroscopy modeling, e.g., transition dipole moments and Dyson orbitals [45,46]. Using EOM-IP-CCSD, we compute a full-dimensional semi-global PES using an invariant polynomial representation [47] as described below.…”

Ionization of cytosine monomer and dimer studied by VUV photoionization and electronic structure calculations

“…The electronic structure of this type of dimers can be described in terms of DMO-LCFMO (dimer molecular orbitals -linear combination of fragment molecular orbitals) framework. 37,64 DMO-LCFMO assumes that the dimer MOs are in-phase and out-of-phase combination of the monomer's MOs, and the states shown in Fig. 7 are of this type.…”

“…Same-magnitude shifts of different sign for ionization from bonding/antibonding pairs of orbitals were observed in a variety of stacked dimers. 22,23,37 Thus, the deviation is likely to be due to the stronger perturbation of the orbitals introduced by hydrogen bonding.…”

The effect of microhydration on ionization energies of thymine

“…This method has been successfully applied to describe electronic structure of ionized benzene dimers [31,33], water clusters [34][35][36] and dimers of nucleobases [3-5, 7, 8].…”