Molecular geometry and excited electronic states. Theoretic study on the molecular geometry and the fluorescence lifetime difference of isometric phenylnapkthalenes1

The equilibrium molecular geometries of 1-phenyl- and 2-phenyl-naphthalenes in the electronic S_o and S₁ states have been calculated by minimization of the total energy with respect to all molecular coordinates. The singlet term systems of both isomers have been determined using these results. Although the fluorescence transition energy is nearly the same in both cases it was found that the corresponding electronic transitions were allowed in 1-phenylnaphthalene but were forbidden in 2-phenylnaphthalene. The result explains the different fluorescence lifetimes observed.     

激发态1，2-二硫环丁烯去活性和异构化机理的理论研究

运用完全活性空间多组态CASSCF方法研究了激发态1,2-二硫环丁烯（1,2-Dithiete）势能面交叉机理．自旋．轨道耦合（SOC）常数采用完全Pauli-Breit旋轨耦合算符（包括单电子和双电子项）进行计算,其强度为198．37或211．35cm^-1,对不同自旋态跃迂起着重要作用．研究结果表明：光激发1,3-dithiol-2-one导致形成主要产物trans—dithioglyoxal（Trans-MinS0）和次级产物thiolthioketene．计算与实验观察结果一致．     

Singly and doubly excited states of butadiene, acrolein, and glyoxal: Geometries and electronic spectra

Excited-state geometries and electronic spectra of butadiene, acrolein, and glyoxal have been investigated by the symmetry adapted cluster configuration interaction (SAC-CI) method in their s-trans conformation. Valence and Rydberg states below the ionization threshold have been precisely calculated with sufficiently flexible basis sets. Vertical and adiabatic excitation energies were well reproduced and the detailed assignments were given taking account of the second moments. The deviations of the vertical excitation energies from the experiment were less than 0.3 eV for all cases. The SAC-CI geometry optimization has been applied to some valence and Rydberg excited states of these molecules in the planar structure. The optimized ground- and excited-state geometries agree well with the available experimental values; deviations lie within 0.03 A and 0.7 degrees for the bond lengths and angles, respectively. The force acting on the nuclei caused by the excitations has been discussed in detail by calculating the SAC-CI electron density difference between the ground and excited states; the geometry relaxation was well interpreted with the electrostatic force theory. In Rydberg excitations, geometry changes were also noticed. Doubly excited states (so-called 2 (1)A(g) states) were investigated by the SAC-CI general-R method considering up to quadruple excitations. The characteristic geometrical changes and large energetic relaxations were predicted for these states.     

Molecular geometry and excited electronic states: Part IV. Theoretical study on molecular geometries and spectral properties of bipyrimidine compounds

The equilibrium geometry of two bipyrimidine photoproducts of nucleic acids in the electronic ground and first excited singlet states has been calculated by minimization of the total energy with respect to all molecular coordinates. Using these results and the method of configuration analysis, this paper discusses whether or not the model of individual chromophores can be invoked to rationalize the spectral properties.     

Molecular geometry and excited electronic states : Part XIII. Conformational geometries of 9,10-diphenyl anthracene in different electronic states and its electronic spectral behaviour

The conformational geometries of 9,10-diphenyl anthracene in the S₀, S₁, and T₁ electronic states determined by means of the Warshel—Karplus method are presented. Based on the theoretical equilibrium geometries of the con- and dis-twisted conformations the calculated electronic transition energies and oscillator strengths are used for an interpretation of the electronic spectral behaviour in absorption and fluorescence. The corresponding theory-experiment comparison performed is satisfactory.     

A theoretical study of the low-lying excited electronic states of thiocarbonyl chlorofluoride and their dissociation pathways

The spectroscopic constants for the ground (X (1)A(1)) and low-lying triplet and singlet excited states (a (3)A("),A (1)A("),B (1)A(')) of thiocarbonyl chlorofluoride (ClFCS) were obtained using the equation-of-motion coupled-cluster singles and doubles method. The calculated vibrational frequencies of the electronic states were within 4% of the experimental values for 21 of the frequencies, but four calculated frequencies were 20%-40% away from the corresponding experimentally reported values, suggesting the need to reexamine previous experimental spectra. The spectroscopic properties of the radical fragments (FCS, ClCS, and CClF) were also studied, and the correlation diagram between the excited electronic states of ClFCS and possible combinations of dissociation fragments were obtained. The potential energy surfaces (PESs) of the excited electronic states of ClFCS along possible dissociation pathways were also studied. The main qualitative dynamical features of the S(1)(A (1)A("))<--S(2)(B (1)A(')) fluorescence of ClFCS, which may occur in spite of the small barrier (8 kcalmol) on the S(2) PES to the dissociation of C-Cl bond, are discussed.     

A self consistent field molecular orbital treatment,including excited states of cyclopropane,ethylene oxide and ethylenimine

The electronic structure of cyclopropane, ethylene oxide and ethylenimine, have been investigated using the Pople-Segal Complete Neglect of Differential Overlap self consistent field molecular orbital method, including all valence electrons. The theory gives a good account of the ground state charge distributions and dipole moments and a reasonable interpretation of the electronic spectra of the three molecules.

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Zusammenfassung Die Elektronenstruktur von Cyclopropan, Äthylenoxid und Äthylenimin wurde mit Hilfe der Pople-Segal CNDO-SCF-MO Methode untersucht. Die Theorie gibt gute Ergebnisse für die Ladungsverteilungen im Grundzustand, für die Dipolmomente und für eine Interpretation der Elektronenspektren.

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Résumé Les structures électroniques du cyclopropane, de l'oxyde d'éthylène et de l'éthylèneimine, ont été étudiées en utilisant la méthode S.C.F. de Pople-Segal comportant tous les électrons de valence et négligeant totalement le recouvrement différentiel. La théorie rend bien compte des distributions de charge et des moments dipolaires de l'état fondamental et donne une interprétation raisonnable des spectres électroniques des trois molécules.

     

A MS-CASPT2 study of the low-lying electronic excited states of CH2BrCl

The low-lying singlet excited states of CH₂BrCl have been calculated using multiconfigurational CASSCF, second-order perturbation theory CASPT2 and its multistate extension MS-CASPT2. The CASSCF method shows spurious valence–Rydberg mixing and a wrong order of states. Inclusion of dynamical correlation by single root CASPT2 lowers dramatically the energy of the valences states but does not lead to a complete separation between valence and Rydberg states. This situation is improved by the MS-CASPT2 calculations, which gives two valence states for both A^′ and A″ symmetries below the lowest Rydberg state, corresponding to n(Br)→σ^*(C–Br) and n(Cl)→σ^*(C–Cl) transitions at 6.1 eV (203 nm) and 7.2 eV (173 nm), and being repulsive along C–Br and C–Cl coordinates.     

The molecular structure and a Renner-Teller analysis of the ground and first excited electronic states of the jet-cooled CS2 + molecular ion

The A 2Pi(u) - X 2Pi(g) electronic band system of the jet-cooled CS2 + ion has been studied by laser-induced fluorescence and wavelength-resolved emission techniques. The ions were produced in a pulsed electric discharge jet using a precursor mixture of carbon disulfide vapor in high-pressure argon. Rotational analysis of the high-resolution spectrum of the 2Pi32 component of the 0(0) 0 band gave linear-molecule molecular structures of r0" = 1.5554(10) A and r0' = 1.6172(12) A. Renner-Teller analyses of the vibronic structure in the spectra showed that the ground-state spin-orbit splitting (A = -447.0 cm(-1)) is much larger than that of the excited state (A = -177.5 cm(-1)), but that the Renner-Teller parameters are of similar magnitude and that a strong nu1 - 2nu2 Fermi resonance occurs in both states. Previous analyses of the vibronic structure in the ground and excited states of the ion from pulsed field-ionization-photoelectron data are shown to be substantially correct.     

Reactivity and electronic structure of the ground and excited states of oxazole, 2-phenyloxazole, and 2-phenylthiazole

The relationship of the electronic structure, of oxazole, 2-phenyloxazole, and 2-phenylthiazole to the properties of the electronic excited states and transitions is examined. Spectral properties of these compounds in the free state (no effect from external perturbations) and in complexes with the proton and aprotic acids are measured and calculated by quantum-chemical PPP/S (-approximation), and INDO/S (sp-basis) methods. Features of the electronic excitation of the atoms and the vibronic interaction of bonds in the singlet and triplet states are examined for a change of the various structural forms of azoles, which determine their spectral fluorescence properties and reactivity. Possible direction control of reactions and optimized syntheses of new compounds with given properties are discussed based on a study of the properties of the ground and excited states.Russian People's Friendship University, Moscow 117302 N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913 Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 948–974, July, 1999.     

Molecular geometry and excited electronic states : Part VII. Theoretical study on conformational geometries and the dual fluorescence of styrene

Equilibrium molecular geometries of styrene in the electronic S₀, S₁, and S₂, states have been calculated within the scope of the adiabatic approximation by minimization of the total energy with respect to all molecular coordinates. Besides the most stable planar structures, some further conformers twisted about the single and/or double bonds have been found. An interpretation of the styrene dual fluorescence is given using these results.     

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.     

Multireference composite approaches for the accurate study of ground and excited electronic states: C2, N2, and O2

A multireference analog of the correlation consistent composite approach (MR-ccCA) based on complete active space with second-order perturbation theory (CASPT2) has been utilized in an investigation of the ground and valence excited states of C(2), N(2), and O(2). The performance of different second-order multireference perturbation theory methods including second-order n-electron valence state perturbation theory, second-order multireference M?ller-Plesset, and second-order generalized van Vleck perturbation theory has been analyzed as potential alternatives to CASPT2 within MR-ccCA. The MR-ccCA-P predicts spectroscopic constants with overall mean absolute deviations from experimental values of 0.0006 A?, 7.0 cm(-1), and 143 cm(-1) for equilibrium bond length (r(e)), harmonic frequency (ω(e)), and term values (T(e)), respectively, which are comparable to the predictions by more computationally costly multireference configuration interaction-based methods.     

A combined quantum mechanical and molecular mechanical method using modified generalized hybrid orbitals: implementation for electronic excited states

The generalized hybrid orbital (GHO) method is implemented at the second-order approximate coupled cluster singles and doubles (CC2) level for quantum mechanical (QM)/molecular mechanical (MM) electronic excited state calculations. The linear response function of CC2 in the GHO scheme is derived and implemented. The new implementation is applied to the first singlet excited states of three aromatic amino acids, phenylalanine, tyrosine, and tryptophan, and also bacteriorhodopsin for assessment. The results obtained for aromatic amino acids agreed well with the full QM CC2 calculations, while the calculated excitation energies of bacteriorhodopsin and its chromophore, all-trans retinal, reproduced the environmental shift of the experimental data. For the bacteriorhodopsin case, the environmental shift of GHO also showed good agreements with the experimental data. The contribution of the quantum effect of certain moieties in the excited states is elucidated by changing the partitioning of QM and MM regions.