Many-electron contributions in the auger spectrum of CO

The CO Auger electron spectrum has been re-investigated by means of ab initio MO LCAO calculations using a combined SCF CI procedure. The CI comprises internal and semi-internal contributions to the final double-hole Slate wave-functions. In particular, the latter contributions are found to be highly significant both with respect to energies and intensities of the Auger transitions. In order to compare with the experimental spectra, the intensities of the transitions have also been calculated using a simple one-center model.     

Electronic transitions in 1,4-naphthoquinone derivatives

Single electronic transitions in 1,4-naphthoquinone and seven of its derivatives substituted in the quinoid system have been theoretically studied semi-empirical SCF MO CI calculations, in the frame of π and all valence electron (AVE) approximations. Dipole electrostatic contributions to the shifts originating from the solvent have been calculated and the local nature of the most significant transitions has been analyzed. The results agree satisfactorily with experiment, showing the effects of the substituents, which in some cases are underestimated.     

Electronic absorption spectra of some nicotinamides and nicotinic acids. Molecular orbital treatment

The electronic absorption spectra of the position isomers nicotinamide and isonicotinamide, nicotinic acid, and isonicotinic acid were investigated, together with the spectra of thionicotinamide, N-methyl nicotinamide and nicotinic acid N oxide. Apparent differences in the spectra of the position isomers were interpreted in terms of the torsion angle between the planes of the molecule, the height of the barrier to internal rotation, and the results of molecular orbital (MO) calculations. The largest perturbation effect was observed in the case of thionicotinamide whereas the smallest effect was observed in the case of nicotinic acid N oxide. MO calculations have indicated the existence of overlapping transitions. The observed transitions proved to be π-π* transitions, none of the n-π* was observed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64 : 689–701, 1997     

Synthesis,spectroscopy, X-ray crystal structure,and DFT studies on a platinum(II) Schiff-base complex

[PtCl₂(SMe₂)₂] reacts with (N,N′-bis(salicylidene)-1,2-cyclohexanediamine) to give (N,N′-bis(salicylidene)cyclohexane-1,2-diamine)platinum(II). The complex has been characterized by elemental analysis, infrared (IR), UV-Vis, and single-crystal X-ray diffraction. Pt(II) is in a square-planar environment, coordinated by a chelating N₂O₂ donor. Density functional theory (DFT) calculations such as geometry optimization, vibrational frequency, electronic properties, and natural bond orbital (NBO) have been performed for the platinum compound using the OLYP method at TZP(6-311G*) basis set. The optimization calculation shows that the geometry parameters can be reproduced with the OLYP/TZP basis set. Experimental IR frequencies and calculated vibrational frequencies support each other. Time-dependent DFT has been used for absorption wavelengths and results were compared with experimental data. Moreover, NBO analysis has been performed.     

Simple calculations of Franck-Condon factors for electronic transition bands of polyacenes

Progressional intensities have been calculated for the L_a and L_b transitions of the polyacenes, on the basis of semi-empirical SCF CI calculations of geometry changes upon electronic excitation and from normal analyses. The results give the Franck-Condon intensity distributions over various totally symmetric modes in good agreement with the vibrational structures observed in high resolution spectra.     

Electronic absorption spectra of V2O5

MO calculations of electronic structure and optical transitions for [VO_n]^{5 ?; 2n} (n = 4, 5, 6) clusters in V₂O₅ monocrystals have been carried out by means of the semiempirical CNDO CI method. Using the calculated results, a complete analysis of V₂O₅ optical data as available in the literature and as obtained in the electroreflectivity experiments presented in this paper is performed. An identification of optical transitions in a wide energy range is presented. The optical properties of vanadium pentoxide are shown to be due to the localized charge transfer electronic transitions in the clusters. The fine structure of optical spectra is connected with the covalent splittings of the vanadium 3d and oxygen 2p atomic levels.     

Synthesis, characterization, crystal structure and DFT studies on 1-acetyl-3-(2,4-dichloro-5-fluoro-phenyl)-5-phenyl-pyrazoline

The title compound, 1-acetyl-3-(2,4-dichloro-5-fluoro-phenyl)-5-phenyl-pyrazoline, has been synthesized and characterized by elemental analysis, IR, UV-vis and X-ray single crystal diffraction. Density functional (DFT) calculations have been carried out for the title compound by using B3LYP method at 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. Predicted vibrational frequencies have been assigned and compared with experimental IR spectra and they are supported each other. The theoretical electronic absorption spectra have been calculated by using TD-DFT method. Molecular orbital coefficients analyses suggest that the above electronic transitions are mainly assigned to n-->pi* and pi-->pi* electronic transitions. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated, revealing the correlations between C(p,m)(0),S(m)(0),H(m)(0) and temperatures.     

Calculations of the optical spectra of hydrocarbon radical cations based on Koopmans' theorem

The first few bands in the optical spectra of radical cations can often be interpreted in terms of A-type transitions that involve electron promotions from doubly occupied to the singly occupied molecular orbital (SOMO) and/or B-type transition which involve electron promotion from the SOMO to virtual molecular orbitals. We had previously demonstrated that, by making use of Koopmans' theorem, the energies of A-type transitions can be related to orbital energy differences between lower occupied MOs and the highest occupied MO (HOMO) in the neutral molecule, calculated at the geometry of the radical cation. We now propose that the energies of B-type transitions can be related similarly to energy differences between the lowest unoccupied MO (LUMO) and higher virtual MOs in the dication, also calculated at the geometry of the radical cation, by way of an extension of Koopmans' theorem to virtual MOs similar to that used sometimes to model resonances in electron scattering experiments. The optical spectra of the radical cations of several polyenes and aromatic compounds, the matrix spectra of which are known (or presented here for the first time), and for which CASSCF/CASPT2 calculations are available, are discussed in terms of these Koopmans-based models. Then the spectra of five poly(bicycloalkyl)-protected systems and that of hexabenzocoronene, compounds not amenable to higher level calculations, are examined and it is found that the Koopmans-type calculations allow a satisfactory interpretation of most of the features in these spectra. These simple calculations therefore provide a computationally inexpensive yet effective way to assign optical transitions in radical ions. Limitations of the model are discussed.     

The role of 2,3-dimethylene-1, 4-cyclohexadiyl diradical as a reactive intermediate in some rearrangement reactions

Quantum chemical CI calculations with the semiempirical MO method SINDO1 are performed to study the rearrangement reactions of 1,2,6,7-octatetraen, 2,3-dimethylenebicyclo(2.2.0)hexane, 3,4-dimethylene-1,5-hexadiene and bicyclo(4.2.0)octa-1,5-diene. It is shown that the most favorable pathway of each of these six rearrangements involves the 2,3-dimethylene-1,4-cyclohexadiyl diradical as an interceptable intermediate. Two further intermediates, 1,2-divinyl-1-cyclobutene and 1,2-divinylylcyclobutane appear, but the latter with little importance. Energies and geometries of the four reactants resp. products, the three intermediates and twelve transitions states are presented. The mechanism of the rearrangements is discussed.     

AM1 CI and ZINDO/S study of quaternary salts of diazaphenanthrenes with haloalkanes

For quaternary salts of diazaphenanthrenes 1-3 with methyl iodide 4-6, diiodomethane 7-9 and 1,2-dibromoethane 10-12 UV spectral values have been calculated by AM1 CI, and in the case of 4-6 also with ZINDO/S method. Correlations of experimental and calculated wavenumber values of considered compounds show good compatibility. For geometry optimisation of 4-9 the AM1 CI method has been used.     

1H NMR spectra of ethane‐1,2‐diol and other vicinal diols in benzene: GIAO/DFT shift calculations

The proton NMR spectra of several 1,2‐diols in benzene have been analysed so as to associate each magnetically nonequivalent proton with its chemical shift. The shifts and coupling constants of the OH and methylene protons of ethane‐1,2‐diol have been determined in a wide range of solvents. The conformer distribution and the proton NMR shifts of these 1,2‐diols in benzene have been computed on the basis of density functional theory. The solvent is included using the integral–equation–formalism polarizable continuum model implemented in Gaussian 09. Relative Gibbs energies for all stable conformers are calculated at the Perdew, Burke and Enzerhof (PBE)0/6‐311 + G(d,p) level, and shifts are calculated using the gauge‐including atomic orbital method with the PBE0/6‐311 + G(d,p) geometry but using the cc‐pVTZ basis set. Previous calculations on ethane‐1,2‐diol and propane‐1,2‐diol have been corrected and extended. New calculations on tert‐butylethane‐1,2‐diol, phenylethane‐1,2‐diol, butane‐2,3‐diols (dl and meso) and cyclohexane‐1,2‐diols (cis and trans) are presented. Overall, the computed NMR shifts are in good agreement with experimental values for the OH protons but remain systematically high for CH protons. Some results based on the Gaussian 03 solvation model are included for comparison. Copyright © 2012 John Wiley & Sons, Ltd.     

Studies on hypersensitive transitions of Nd(III) in Nd(III)-0-diketone-neutral ligand ternary compounds

In this paper, hypersensitive transitions of Nd( I) in Nd( I )-β-diketone-neutra] ligand ternary coordination compounds (where p-diketone = acetylacetone (AA), benzoylacetone (BA), dibenzoylmethane (DBM), 2-thenoyl trifluoroacetone (TTA); neutral ligand = pyridine (Py). cr.a′-dipyridyl (Dipy), phenanthroline (Phen) are studied and their intensities are given through dynamic coupling model. The results are in agreement with those observed and calculated using Judd-Ofelt equation. It may be seen that the dynamic coupling mechanism provides major contribution to the intensity of hypersensitive transition. On the other hand, in order to get the intensity of 4I_9/1→4G_5/2 transition, the absorption spectra in 560–610 nm have been decomposed into three peaks by nonlinear fitting with Lorentzian and Gaussian function and the “pure” intensities of hypersensitive transitions have been obtained, which are agreeable to those computed by Judd-Ofelt method and dynamic coupling model.     

Molecular electronic structure of metal phthalocyanines

The molecular–electronic structure of the metal phthalocyanines (Fe, Co, Ni and Cu) has been determined by the molecular orbital treatment. Coulomb integrals of the metal atom occurring in the secular determinants have been approximated equivalent to the valence state ionization energy (VSIE) of a metal orbital for a particular charge configuration. The calculated π-electron charge densities have been found to be higher on the nitrogen atoms as compared to the other atoms in the molecule. This is in agreement with the e.s.r. studies of the metal phthalocyanines. To test the correctness of the molecular orbital calculations, the π-π* transitions (14,000 cm^?1 ? 30000 cm^?1), d-d* transitions (20000 cm^?1 ? 60000 cm^?1) and charge transfer transitions (15000 cm ^?1 ? 30000 cm^?1) have been calculated in the metal phthalocyanine molecules. The calculated frequencies have been compared with the observed ones and found in fair agreement.     

FT-IR, FT-Raman, ab initio and DFT structural, vibrational frequency and HOMO-LUMO analysis of 1-naphthaleneacetic acid methyl ester

In this work, the FT-IR and FT-Raman spectra of 1-naphthaleneacetic acid methyl ester (abbreviated as 1-NAAME, C₁₀H₇CH₂CO₂CH₃) have been recorded in the region 3600–10 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, corresponding vibrational assignments, Mullikan atomic charges and other thermo-dynamical parameters were investigated with the help of HF and B3LYP (DFT) method using 6-31G(d,p), 6-311G(d,p) basis sets. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures were fitted by quadratic formulae. Lower value in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. UV–VIS spectral analyses of 1NAAME have been researched by theoretical calculations. In order to understand electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths (λ), oscillator strengths (f) and excitation energies (E) for gas phase and solvent (DMSO and chloroform) are also illustrated.     

Experimental and theoretical study on cation radicals of cyclopropane,cyclobutane and cyclopentane

Cation radicals of cycloalkanes have been produced for the first time in γ-irradiated rigid solutions using fluoromethane as a matrix. Observed ESR spectra are analyzed by ab initio MO calculations; molecular geometries of the cations are optimized for several low-lying doublet states by the energy gradient method. Based on the optimized geometry thus determined the hyperfine splitting constants are calculated by the pseudo-orbital theory. Large Jahn-Teller distortions are calculated for the carbon rings and the H-C-H frames of the cation radicals. The distortions are consistent with the nodal picture of singly occupied orbitals. The calculated hfs constants are sensitive to the change in geometry due to a large contribution of spin-delocalization. The average of the calculated proton hfs constants is compatible with the observed ESR spectra which indicates that all the protons of the individual cations have become equivalent owing to the dynamic Jahn-Teller distortion.     

Molecular structure and electronic spectrum of ellagic acid: Semiempirical molecular orbital calculations

The molecular structure of ellagic acid has been optimized by using PM3 semiempirical MO method. Ellagic acid has been calculated to be planar with the molecular symmetry of C_2h. The lactone carbonyl groups are not tilted from the molecular plane. CNDO/S MO method has been used to interpret the experimental uv-vis spectroscopic data. The results of the PM3 and CNDO/S calculations have been in good agreement with the experimental data.     

四苯硼阴离子电子结构的理论研究

分别应用半经验发子轨道理论的AM1方法和在HF／3－21G水平上的从头算分子轨道法,对四苯硼阴离子的电子结构进行了研究。采用解析梯度技术对四苯硼阴离子的平衡态几何构型进行了全优化,得到了分子轨道、电荷布居、静电势以及红外光谱和紫外光谱等参数,计算结果表明：四苯硼阴离子的静电势分布均匀,其前线轨道能级间隔为12．1398eV,利用组态相互作用法得到的紫外光谱跃迁吸收峰主要位于远紫外区,说明四苯硼离子比较稳定,从头算法得到的红外光谱吸收峰分布与实验结果一致,AM1法得到的红外吸收频率与实验值更接近。     

Halogen bonding driven self-assembly of (E)-1,2-diiodo-1,2-difluoroethene with nitrogen substituted hydrocarbons

N?I halogen bondings drive the intermolecular recognition between (E)-1,2-diiodo-1,2-difluoroethene, which work as bidentate electron acceptor, and TMEDA or 4,4′-dipyridyl, which work as bidentate electron donors. The presence of 1D infinite chains in both co-crystals has been established through X-ray analyses.     

Quantum-chemical study of crystal formation of supramolecular silver compounds with trans-1,2-Bis(4-pyridyl)ethylene and their electronic absorption spectra

The energies of singlet-singlet transitions in different supramolecular compounds formed by interaction of trans-1,2-bis(4-pyridyl)ethylene (DPyEt) with AgNO₃ have been calculated by the TDDFT method. The calculations show that the absorption peaks at 305.7 and 318.3 nm can be assigned to a superposition of the spectra of small suprastructures, e.g., (Ag)(DPyEt)₂(NO₃), (Ag)₂(DPyEt)(NO₃)₂, and (Ag)(DPyEt)(NO₃). These transitions correspond to the excitation of an electron from the bonding orbital into the antibonding orbital with respect to the C=C bond. Strong absorption bands at 350–360 nm, typical of a solid phase, can be assigned to the transition from the MO of the lone pair of the nitrogen of DPyEt into the antibonding MO with respect to the C=C bond. Such bands are present in the calculated excitation spectra of the (Ag)₁(DPyEt)₃(NO₃)₁ and (Ag)₂(DPyEt)₄(NO₃)₂ suprastructures.     

Infrared and Raman spectra, conformational stability, ab initio calculations and vibrational assignment for 1,2-pentadiene (ethyl allene)

The infrared (3500-50 cm⁻¹) and Raman (3500-20 cm⁻¹) spectra of 1,2-pentadiene, H₂C=C=C(H)CH₂CH₃ (ethyl allene), have been recorded for both the gaseous and solid states. Additionally, the Raman spectrum of the liquid has been obtained with qualitative depolarization values. In the fluid phases both the cis and gauche conformers have been identified, with the gauche rotamer being the predominant form although it may not be the conformer of lowest energy. In the solid state only the cis conformer remains after repeated annealing of the crystal. The asymmetric torsion of the cis conformer is observed as a series of Q-branch transitions beginning at 103.4 cm⁻¹ and falling to lower frequency. An estimate of the potential function governing conformer interconversion is provided. A complete assignment of the normal modes for the cis conformer is given and several of the fundamentals are assigned for the gauche rotamer. Ab initio electronic structure calculations of energies, conformational geometries, vibrational frequencies, and potential energy functions have been made to complement and assist the interpretation of the infrared and Raman spectra. In particular, the transitions among torsional energy levels for both the symmetric (methyl) and asymmetric (ethyl) motions have been calculated. The results are compared to the corresponding quantities for some similar molecules.