Expanded electronic states of the fluorine molecule

Potential curves of electronically excited states of F₂ with an expanded outer orbital have been calculated using a modified frozen core technique: The ionic core has been described with a two-determinant wave function and for the excited states a mixing of configurations with different cores has been employed. An investigation of the valence shell states of F₂ is presented and potential curves for a singly excited as well as a doubly excited V-state of ¹Σ_u⁺ symmetry have been calculated. Further a low lying two-configuration state resulting from simultaneous excitation to a valence and a Rydberg orbital is predicted.     

Intramolecular interactions in the triplet excited states of benzophenone-thymine dyads

Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine.     

The orbital description of the potential energy curves and properties of the lower excited states of the BH molecule

The electronic wavefunctions for the ground (X¹ Σ⁺) and the low-lying excited states (a³Π, A¹Π, ³Σ⁺) of the BH molecule have been calculated as a function of internuclear distance using the ab initio generalized valence bond method (GVB) with optimization of spin coupling (SOGI). The potential curve of the A¹Π state in the zero rotational level is found to have a hump of 0.150 eV at R = 3.8₉a_o (experimentally a hump of unknown size is found at 3.9 ± 0.4 a₀); a smaller hump at larger R (0.02 eV at R = 4.9₂a₀) is also found for the calculated a³Π state. The presence of such humps is found to result from the recoupling of orbitals that must occur as R is decreased from ∞ to R_e and is comparable in origin to the activation barrier in a radical exchange reaction (e.g., H₂ + D ? HD + H). The calculated binding energies of the BH states are 3.272 eV (X¹ Σ⁺), 2.216 eV (a³ Π), and 0.502 eV (A¹ Π). The ³Σ⁺ state is unbound although it does exhibit a small unbound minimum. The dipole moment, quadrupole moment, and electric field gradient are calculated as a funtion of R. The shapes of the potential curves and the properties are interpreted in terms of simple qualitative considerations of the GVB orbitals.     

Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling lignin. III. Quinones and quinone methides

An investigation has been made by the CNDO/S method with allowance for configurational interaction (the lowest six vacant and the highest eight occupied MMOs) of the electronic structure of a number of quinones and quinone methides forming component parts of the structural unit of lignin. The energies of the first singlet-singlet and singlet-triplet transitions and the redistribution of charges on excitation have been obtained, and the dependence of the energy of the transitions on the chromophores present in the molecule has been discussed. The change in the donor-acceptor properties of the fragments in excited states, leading to a change in the pathways in nucleophilic and electrophilic reactions has been shown.     

Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling lignin. III. Quinones and quinone methides

An investigation has been made by the CNDO/S method with allowance for configurational interaction (the lowest six vacant and the highest eight occupied MMOs) of the electronic structure of a number of quinones and quinone methides forming component parts of the structural unit of lignin. The energies of the first singlet-singlet and singlet-triplet transitions and the redistribution of charges on excitation have been obtained, and the dependence of the energy of the transitions on the chromophores present in the molecule has been discussed. The change in the donor-acceptor properties of the fragments in excited states, leading to a change in the pathways in nucleophilic and electrophilic reactions has been shown.A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 858–865, November–December, 1988.     

Intramolecular electronic interactions in conjugated ferrocene-pi-extended-tetrathiafulvalene donor-pi-donor molecular hybrids

The synthesis of new hybrid ferrocene and pi-extended tetrathiafulvalene (TTF) donor(1)-pi-donor(2) molecular assemblies 16a-c has been carried out by a Wittig-Horner reaction of the respective phosphonate esters 15a-c with 2-(2-ferrocenylvinyl)-9, 10-anthraquinone (18) prepared by olefination of ferrocenecarboxaldehyde (14) and the anthraquinone phosphonium salt 17. Electrochemical studies show that the D(1)-pi-D(2) (D = donor) molecular assemblies 16a-c essentially retain the redox characteristics of both ferrocene and the pi-extended TTF components and the effects of solvent, temperature, scan rate, and working electrode are significant. Most importantly, pronounced intramolecular electronic interactions between the two donor moieties were observed by cyclic voltammetry and Osteryoung square wave voltammetry in both the ground and charged states. Semiempirical calculations support the electrochemical observations.     

Theoretical electronic structure of the lowest-lying states of the YI molecule

CAS-SCF/MRCI calculations have been performed for 15 molecular states in the representation ^2S+1Λ^(+/−) (neglecting spin–orbit effects) for the molecule YI. The corresponding 33 molecular states in the representation Ω^(+/−) (including spin–orbit effects) have been calculated using a semi-empirical spin–orbit pseudopotential built up for yttrium. Calculated potential energy curves and spectroscopic constants are reported, to the best of our knowledge they are the first ones from ab initio methods for this molecule. Present results are compared to experimental accurate data available for the ground X¹Σ⁺ and 3 excited states (1)¹Π, (2)¹Σ⁺ and (2)¹Π.     

Intramolecular orbital interactions in and conformation of N,N′-diphenylcarbodiimide studied by photoelectron spectroscopy

The intramolecular orbital interactions in N,N′-diphenylcarbodiimide were revealed by photoelectron spectroscopy and the phenyl rings in this compound were found to be twisted by ca. 25° from the perpendicular model.     

Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling the structural unit of lignin. II. Phenolate anions

Quantum-chemical calculations of the electronic structures of the phenolate ions of compounds modeling lignin in the ground and electronically excited states have been made by the CNDO/S method. The intramolecular electron donor-acceptor interactions in the phenolate anion on excitation and the nature of the lowest electronically excited states are discussed on the basis of the results obtained.Siberian Scientific-Research Institute of Pulp and Board, Bratsk. A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 275–282, March–April, 1988.     

Configuration analysis and electronic states properties

The excited-states electronic properties of unsaturated small-ring hydrocarbons with four- and six--electrons have been studied by the Molecules in Molecules method and compared with experimental data and PPP results interpreted through a configuration analysis procedure. The results show that the MIM method is applicable with good reliability.

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Zusammenfassung Die elektronischen Eigenschaften der angeregten Zustände von ungesättigten kleinen Kohlenwasserstoffringen mit vier und sechs -Elektronen wurden mit Hilfe der Molekül- im-Molekül-Methode untersucht und die Ergebnisse mit experimentellen Daten und PPP Resultaten, die durch eine Konfigurationsanalyse interpretiert wurden, verglichen. Die Ergebnisse zeigen, daß die MIM-Methode mit großer Zuverlässigkeit anwendbar ist.

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Financial aid from the Italian C.N.R. is gratefully acknowledged.     

Intramolecular interactions and nature of the lowest electronically excited states in compounds modeling the structural unit of lignin. I. Molecular form

Quantum-chemical calculations of the electronic structure of molecules of model compounds of lignin in the ground and electronically excited states have been made by the CNDO/S method. The paper gives results on the energies and strengths of the oscillators of the electronic transitions and on the type of excited singlet and triplet states, shows the main configurations of the HOMOs and LUMOs participating in the transitions and their energies and statistical weights, and gives the distribution of charges and their redistribution on the passage of the molecules from the ground into the excited states. Donor-acceptor interactions in the molecules under investigation are discussed on the basis of the results obtained.Siberian Scientific-Research Institute of Pulp and Board, Bratsk. A. A. Zhdanov Irkutsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 265–274, March–April, 1988.     

Theoretical calculation of the low-lying sextet electronic states of CrF molecule

The potential energy curves have been investigated for the 12 lowest sextet electronic states in the ^2s+1Λ^(±)${}^{2s+1}{\mathrm{\Lambda }}^{(\pm )}$ representation below 53,000 cm⁻¹ of the molecule CrF via CASSCF and MRCI (single and double excitation with Davidson correction) calculations. Seven electronic states have been studied theoretically for the first time. The harmonic frequency ω_e, the internuclear distance R_e, the rotational constant B_e, the electronic energy with respect to the ground state T_e, and the permanent dipole moment μ have been calculated. By using the canonical functions approach, the eigenvalues E_v, the rotational constant B_v and the abscissas of the turning points R_min and R_max have been calculated for the considered electronic states up to the vibrational level v = 39. The comparison of these values to the theoretical and experimental results available in the literature shows a good agreement.     

The nature of the electronic states and photoelectron spectra of oxyanion crystals

The densities of states, atomic charges, and partial components were calculated by the B3LYP method for lithium, sodium, and potassium nitrites, nitrates, chlorates, perchlorates, sulfites, and sulfates using a localized basis of atomic orbitals and CRYSTAL06 software. The calculated densities of states N(E) are in good agreement with the experimental photoelectron spectrum (UPS). The crystallographically nonequivalent metal and oxygen atoms are in different charged states, which leads to a splitting of the N(E) bands.     

A reassignment of molecular orbital configurations of the electronic states of ScF

Ab initio molecular orbital calculations have been performed on low-lying electronic states of ScF. The calculations suggest a reassignment of the molecular orbital configurations of the lowest lying Φ states, and suggest also that some of the low-lying Π states may not be well described by single configuration wavefunctions.     

酞菁铜分子的电子态和反饱和吸收

用ROHF-INDO/SDCI方法结合实验研究了酞菁铜分子的电子的电子结构.紫外-可见光谱.激发态分子动态学和反饱和吸收的微观机制.对酞菁铜实现反饱和吸收的必要条件是最低四重态对激光的吸收截面必须大于基态对激光的吸收截面. 在波长为532nm的激光作用下.该条件得到了满足,故Cupc呈现反饱和吸收特征.理论分析与实验结果一致.     

Electronically excited states of water clusters of 7-azaindole: structures, relative energies, and electronic nature of the excited states

The geometries of 1H-7-azaindole and the 1H-7-azaindole(H(2)O)(1-2) complexes and the respective 7H tautomers in their ground and two lowest electronically excited pi-pi(*) singlet states have been optimized by using the second-order approximated coupled cluster model within the resolution-of-the-identity approximation. Based on these optimized structures, adiabatic excitation spectra were computed by using the combined density functional theory/multireference configuration interaction method. Special attention was paid to comparison of the orientation of transition dipole moments and excited state permanent dipole moments, which can be determined accurately with rotationally resolved electronic Stark spectroscopy. The electronic nature of the lowest excited state is shown to change from L(b) to L(a) upon water complexation.     

Theoretical study of spectroscopic and molecular properties of several low‐lying electronic states of CO molecule

The potential energy curves (PECs) of eight low‐lying electronic states (X¹Σ⁺, a³Π, a′³Σ⁺, d³Δ, e³Σ^?, A¹Π, I¹Σ^?, and D¹Δ) of the carbon monoxide molecule have been studied by an ab initio quantum chemical method. The calculations have been performed using the complete active space self‐consistent field method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation‐consistent aug‐cc‐pV5Z basis set. The effects on the PECs by the core‐valence correlation and relativistic corrections are included. The way to consider the relativistic corrections is to use the third‐order Douglas–Kroll Hamiltonian approximation at the level of a cc‐pV5Z basis set. Core‐valence correlation corrections are performed using the cc‐pCVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size‐extensivity errors by means of the Davidson modification (MRCI+Q). The spectroscopic parameters (D_e, T_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e, α_e, and γ_e) of these electronic states are calculated using these PECs. The spectroscopic parameters are compared with those reported in the literature. Using the Breit–Pauli operator, the spin–orbit coupling effect on the spectroscopic parameters is discussed for the a³Π electronic state. With the PECs obtained by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations, the complete vibrational states of each electronic state have been determined. The vibrational manifolds have been calculated for each vibrational state of each electronic state. The vibrational level G(ν), inertial rotation constant B_ν, and centrifugal distortion constant D_ν of the first 20 vibrational states when the rotational quantum number J equals zero are reported and compared with the experimental data. Comparison with the measurements demonstrates that the present spectroscopic parameters and molecular constants determined by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations are both reliable and accurate. © 2012 Wiley Periodicals, Inc.     

On electronic states and bond lengths of the truncated icosahedral C60 molecule

The electronic states and the bond lengths of the truncated icosahedral C₆₀ molecule have been calculated by the Hückel and Coulson-Golebiewski self-consistent Hückel methods. C₆₀ has a stable closed shell with a rather big energy gap (= 0.847β) between the HOMO and the LUMO. We have obtained two kinds of bond lengths r₁ = 1.434 Å and r₂ = 1.403 Å, which correspond to the edges of the regular pentagon and the edge of a hexagon not lying on a pentagon.