Separation of isomers by dimer formation: isomerically pure benzene+ and toluene+ ions, and their dimers: ab initio calculations on (benzene)2+

Ibrahim, Yehia; Alsharaeh, Edreese; Rusyniak, M.; Watson, Simon P.; Meot‐Ner, Michael; El‐Shall, M. Samy

doi:10.1016/j.cplett.2003.08.086

Cited by 15 publications

(22 citation statements)

References 24 publications

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“…For the sandwich isomers, the binding energies are ϳ20 kcal/ mol, in agreement with the experimental studies setting it in the 15-20 kcal/mol range. [69][70][71][72][73][74][75] The t-shaped isomer is ϳ7 kcal/ mol less strongly bound. Inclusion of triple excitations in the description of the cation has a small effect on the binding energies, lowering them to less than 0.5 kcal/mol.…”

Section: B Binding Energiesmentioning

confidence: 99%

Charge localization and Jahn–Teller distortions in the benzene dimer cation

Pieniazek

Bradforth

Krylov

2008

The Journal of Chemical Physics

105

139

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Jahn-Teller (JT) distortions and charge localization in the benzene dimer cation are analyzed using the equation-of-motion coupled cluster with single and double substitutions for ionization potential (EOM-IP-CCSD) method. Ionization of the dimer changes the bonding from noncovalent to covalent and induces significant geometrical distortions, e.g., shorter interfragment distance and JT displacements. Relaxation along interfragment coordinates lowers the energy of the t-shaped and displaced sandwich isomers by 0.07 and 0.23 eV, respectively, whereas JT displacements result in additional 0.18 and 0.23 eV. Energetically, the effect of JT distortion on the dimer is similar to the monomer where JT relaxation lowers the energy by 0.18 eV. While the change in the interfragment distance has dramatic spectroscopic consequences, the JT distortion causes only a small perturbation in the electronic spectra. The two geometrical relaxations in the t-shaped isomer lead to opposing effects on hole localization. Intermolecular relaxation leads to an increased delocalization, whereas JT ring distortion localizes the charge. In the sandwich isomers, breaking the symmetry by ring rotation does not induce considerable charge localization. The optimization and property calculations were performed using a new implementation of EOM-IP-CCSD energies and gradients in the Q-CHEM electronic structure package.

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Section: B Binding Energiesmentioning

confidence: 99%

Charge localization and Jahn–Teller distortions in the benzene dimer cation

Pieniazek

Bradforth

Krylov

2008

The Journal of Chemical Physics

105

139

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“…28 Ground state binding energy ͑BE͒ in the gas phase has been measured to be in the range 15-20 kcal/ mol. [37][38][39][40][41][42][43] Several computational studies have investigated the ground state structures of the dimer cation. 41,[43][44][45][46][47] Milosevich et al 44 suggested a displaced sandwich structure based on Hartree-Fock calculations.…”

Section: Introductionmentioning

confidence: 99%

“…Density functional calculation predicts the ground state to have a sandwich structure. 43,47 The most exhaustive study to date is due to Miyoshi et al, 45,46 who characterized both ground and excited states of the dimer cation. In the earlier work, 45 they employed the complete active space self-consistent field ͑CASSCF͒ and multireference configuration interaction with singles and doubles ͑MR-CISD͒ methods to investigate the electronic structure of sandwich, displaced sandwich, and t-shaped isomers.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of the benzene dimer cation

Pieniazek

Krylov

Bradforth

2007

The Journal of Chemical Physics

128

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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.

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“…Several which is slightly less stable (about 2 kcal mol −1 ) than the two sandwich displaced isomers. DFT calculations [43][44][45] performed with the B3LYP functional give reasonable binding energies for the sandwhich structure (17-19 kcal mol −1 ) but underestimate the energy difference between the two structures due to an over-stabilization of the T-shaped structure. In the following, we will use the EOM-IP-CCSD 41,42 results as references to benchmark our method as they are the most recent ab initio calculations and the corresponding binding energies for the most stable structures around 20 kcal/mol (see Table 1 are in good agreement with the experimental studies providing values in the 15-20 kcal/mol range 44,[46][47][48][49][50][51] .…”

Section: Benzene Dimermentioning

confidence: 99%

Modeling Charge Resonance in Cationic Molecular Clusters: Combining DFT-Tight Binding with Configuration Interaction

Rapacioli

Spiegelman

Scemama

et al. 2010

J. Chem. Theory Comput.

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In order to investigate charge resonance situations in molecular complexes, Wu et al. (J. Chem. Phys. 2007, 127, 164119) recently proposed a configuration interaction method with a valence bond-like multiconfigurational basis obtained from constrained DFT calculations. We adapt this method to the Self-Consistent Charge Density-Functional-based Tight Binding (SCC-DFTB) approach and provide expressions for the gradients of the energy with respect to the nuclear coordinates. It is shown that the method corrects the wrong SCC-DFTB behavior of the potential energy surface in the dissociation regions. This scheme is applied to determine the structural and stability properties of positively charged molecular dimers with full structural optimization, namely, the benzene dimer cation and the water dimer cation. The method yields binding energies in good agreement with experimental data and high-level reference calculations.

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Separation of isomers by dimer formation: isomerically pure benzene+ and toluene+ ions, and their dimers: ab initio calculations on (benzene)2+

Cited by 15 publications

References 24 publications

Charge localization and Jahn–Teller distortions in the benzene dimer cation

Charge localization and Jahn–Teller distortions in the benzene dimer cation

Electronic structure of the benzene dimer cation

Modeling Charge Resonance in Cationic Molecular Clusters: Combining DFT-Tight Binding with Configuration Interaction

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