Electronic Structure Of Benzene Research Articles

Adsorption of benzene on defective Pt surfaces: A DFT study

Defects occur naturally on surfaces during formation. The interaction of a benzene molecule with a defective surface of platinum is investigated using plane wave DFT. Adsorption energy, adsorbate geometry and electronic structure of benzene on defective surfaces of platinum is obtained and compared with those on a perfect platinum (111) facet. We observe that the presence of defects in the form of steps and vacancy leads to an increase in the strength of adsorption. It is found that the atop is the most stable site for adsorption on a Pt (111) surface having a vacancy defect, which agrees with the available experimental results. The terrace region, which has a symmetry similar to a perfect Pt(111) surface, gives the 3-fold symmetric fcc hollow site as energetically preferred for adsorption. The step edge has the hcp hollow as the preferred site for adsorption. Analysis of electronic structure and charge transfer at the preferred sites is performed. The presence of defects brings out major changes in adsorption process, as compared to that on perfect surfaces. Reduction in coordination of surface sites due to defects is identified as the main reason for more reactive nature of defective surfaces.

Interplay of Open-Shell Spin-Coupling and Jahn-Teller Distortion in Benzene Radical Cation Probed by X-ray Spectroscopy.

We report a theoretical investigation and elucidation of the X-ray absorption spectra of neutral benzene and of the benzene cation. The generation of the cation by multiphoton ultraviolet (UV) ionization and the measurement of the carbon K-edge spectra of both species using a table-top high-harmonic generation source are described in the companion experimental paper [Epshtein, M.; et al. J. Phys. Chem. A http://dx.doi.org/10.1021/acs.jpca.0c08736]. We show that the 1sC → π transition serves as a sensitive signature of the transient cation formation, as it occurs outside of the spectral window of the parent neutral species. Moreover, the presence of the unpaired (spectator) electron in the π-subshell of the cation and the high symmetry of the system result in significant differences relative to neutral benzene in the spectral features associated with the 1sC → π* transitions. High-level calculations using equation-of-motion coupled-cluster theory provide the interpretation of the experimental spectra and insight into the electronic structure of benzene and its cation. The prominent split structure of the 1sC → π* band of the cation is attributed to the interplay between the coupling of the core → π* excitation with the unpaired electron in the π-subshell and the Jahn-Teller distortion. The calculations attribute most of the splitting (∼1-1.2 eV) to the spin coupling, which is visible already at the Franck-Condon structure, and we estimate the additional splitting due to structural relaxation to be around ∼0.1-0.2 eV. These results suggest that X-ray absorption with increased resolution might be able to disentangle electronic and structural aspects of the Jahn-Teller effect in the benzene cation.

On the electronic structure of benzene and borazine: an algebraic description

The spectrum of a hexagonal ring is analysed using concepts of group theory and a tight-binding model with first, second and third neighbours. The two doublets in the spectrum are explained with the C3 symmetry group together with time-reversal symmetry. Degeneracy lifts are induced by means of various mechanisms. Conjugation symmetry breaking is introduced via magnetic fields, while C3 breaking is studied with the introduction of defects, similar to the inclusion of fluorine atoms. Concrete applications to benzene and borazine are shown as an illustration of our description. Wave functions are described in connection with partial or full aromaticity. Electronic density currents are found for all cases. A detailed study of a supersymmetry in a 6-ring is presented and its consequences on electronic spectra are discussed.

The electronic structure of benzene from a tiling of the correlated 126-dimensional wavefunction

The electronic structure of benzene is a battleground for competing viewpoints of electronic structure, with valence bond theory localising electrons within superimposed resonance structures, and molecular orbital theory describing delocalised electrons. But, the interpretation of electronic structure in terms of orbitals ignores that the wavefunction is anti-symmetric upon interchange of like-spins. Furthermore, molecular orbitals do not provide an intuitive description of electron correlation. Here we show that the 126-dimensional electronic wavefunction of benzene can be partitioned into tiles related by permutation of like-spins. Employing correlated wavefunctions, these tiles are projected onto the three dimensions of each electron to reveal the superposition of Kekulé structures. But, opposing spins favour the occupancy of alternate Kekulé structures. This result succinctly describes the principal effect of electron correlation in benzene and underlines that electrons will not be spatially paired when it is energetically advantageous to avoid one another.

Photophysics of fluorinated benzene. III. Hexafluorobenzene

A theoretical study of the photoabsorption spectroscopy of hexafluorobenzene (HFBz) is presented in this paper. The chemical effect due to fluorine atom substitution on the electronic structure of benzene (Bz) saturates in HFBz. State- of-the-art quantum chemistry calculations are carried out to establish potential energy surfaces and coupling surfaces of five energetically low-lying electronic (two of them are orbitally degenerate) states of HFBz. Coupling of these electronic states caused by the Jahn-Teller (JT) and pseudo-Jahn-Teller (PJT) type of interactions are examined. The impact of these couplings on the nuclear dynamics of the participating electronic states is thoroughly investigated by quantum mechanical methods and the results are compared with those observed in the experiments. The complex structure of the S(1) ← S(0) absorption band is found to originate from a very strong nonadiabatic coupling of the S(2) (of πσ* origin) and S(1) (of ππ* origin) state. While S(2) state is orbitally degenerate and JT active, the S(1) state is nondegenerate. These states form energetically low-lying conical intersections (CIs) in HFBz. These CIs are found to be the mechanistic bottleneck of the observed low quantum yield of fluorescence emission, non overlapping absorption, and emission bands of HFBz and contribute to the spectral width. Justification is also provided for the observed two peaks in the second absorption (the unassigned "c band") band of HFBz. The peaks observed in the third, fourth, and fifth absorption bands are also identified and assigned.

Renormalization of Molecular Electronic Levels at Metal-Molecule Interfaces

The electronic structure of benzene on graphite (0001) is computed using the GW approximation for the electron self-energy. The benzene quasiparticle energy gap is predicted to be 7.2 eV on graphite, substantially reduced from its calculated gas-phase value of 10.5 eV. This decrease is caused by a change in electronic correlation energy, an effect completely absent from the corresponding Kohn-Sham gap. For weakly coupled molecules, this correlation energy change can be described as a surface polarization effect. A classical image potential model illustrates the impact for other conjugated molecules on graphite.

Relaxing the graphite lattice along critical directions: The effect of the electron–phonon coupling on the π electron band structure

We investigate the effects on the electronic structure induced by a relaxation of the graphite lattice along the direction of the phonons associated to the G and to the D peak characteristic of the Raman spectra of graphitic materials. To this aim the bond length dependence of the hopping integral β is introduced in a Hückel (tight-binding) hamiltonian, giving rise to two different β 1 and β 2 parameters. A Peierls-like gap opening is found for a relaxation along the D peak phonon and not for the G peak phonon. The electronic density of states is discussed and a link is shown between the electronic structure of benzene and the electronic structure of graphene at the K point in reciprocal space.

100. Geburtstag von Erich Hückel

AbstractThe theoretical physicist Erich Hückel, who would have become 100 years old on August 9, 1996, was one of the pioneers of quantum chemistry. The theory of conductivity of strong electrolytes (“Debye‐Hückel theory”) and particularly his fundamental work about the electronic structure of benzene, which has unbroken actuality for modern chemistry, are the early highlights of his peculiar scientific career. His life was strongly characterized by the late recognition of his achievements in theoretical chemistry, which can partly be explained by the dominance of experimental chemistry in the history of the science, and by the long uncertainty of his academic position.

Adsorption and Electronic States of Benzene on Ordered MgO and Al2O3 Thin Films

The adsorption and electronic structure of benzene (C6H6) on thin film MgO(100)/Mo(100) and highly ordered Al2O3/Mo(110) substrates have been studied using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Three desorption states have been found for both surfaces. The first corresponds to adsorption of the aromatic ring plane parallel to the surface at low coverages (≤1 ML). Intermediate coverages (>1 ML) give rise to a desorption at a slightly lower temperature, corresponding to the metastable, upright (end-on) adsorption of benzene on the monolayer-covered surface. Large exposures of benzene yield the multilayer with an anomalous higher temperature desorption sequence in the TPD. Both surfaces reveal spectroscopic windows by HREELS between the phonon modes and optical band gap transitions which allow identification of benzene electronic and vibronic transitions. This window is between 2.5 and 5.5 eV in MgO/Mo(100) and 2.5 and 6.7 eV in Al2O3/Mo(110)....

The electronic structure of benzene

Benzene has been studied in a photoelectron spectrometer up to 26 eV. The intensities in the spectrum have been found to be approximately proportional to the number of electrons in the corresponding orbitals, if the interpretation of the benzene spectrum by Jonsson and Lindholm is used. Some orbitals built-up from carbon 2s can be identified by comparison with theoretical calculations. In this way the 2s orbital with the lowest ionization potential can be identified.

The electronic structure of benzene

The orbital energies of benzene from photoelectron spectroscopy measurements have been discussed by use of electron impact energy loss measurements and mass-spectrometric measurements. Between the π-orbitals at 9.3 eV and 12.1 eV there is a σ-orbital at 11.4 eV. Also the remaining molecular orbitals have been identified.

The electronic structure of benzene

Calculations of the energy of the six electrons occupying theπ-orbital system of benzene have been made by the use of functions in which each electron is assigned to a separate two-centre orbital associated with each of the six bonds. The energy obtained by using such a function is lower than any obtained up to the present time by means of other simple approximate functions which are also based on carbon 2pπatomic orbitals. Moreover, the energy calculated is only 2·1 kcal/mole greater than that obtained from a complete configuration interaction treatment involving 22 configurations, and therefore 21 adjustable constants. The present treatment uses only two; moreover, two simpler proposed treatments based on the same type of function but involving only one adjustable constant are almost as successful. The results indicate that this type of function allows for electron correlation arising from electrostatic repulsion more successfully than does the alternant molecular orbital method. Some calculations have also been carried out for the lowest levels of other symmetry classes. These show that this type of function is successful for these also.