Fluorescence of pyrene in the presence of silver nanoparticles on cellulose modified by surface-active substances

Luminescent properties of pyrene in the ordered structure formed by the molecules of a surface-active substance represented by cetyltrimethylammonium bromide on a cellulose matrix preliminarily modified with silver nanoparticles are studied. Elevated intensity of fluorescence in the violet range of the spectrum of pyrene molecules solubilized in these structures is observed. This phenomenon is rationalized by the resonance of electron transitions of monomeric pyrene molecules in this range with plasmonic vibrations in silver nanoparticles.

     

Mechanisms of charge separation in bacterial photosynthesis

The physical aspects of the primary charge separation processes in bacterial photosynthesis are discussed. The donor-acceptor model of electron transfer due to participation of protein current states is used. The kinetics of photosynthetic reaction center (PRC ) processes is investigated and the PRC energetic scheme is constructed using the nonequilibrium density matrix method. It is shown that with allowance for the effect of vibrational sublevels of states participating in transitions the theory describes well experimental data.     

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.     

Laser field dependence of intersubband transition in inverse V‐shaped quantum wells

The electron energy levels and the envelope wave functions in inverse GaAs/AlGaAs V‐shaped quantum wells (QWs) are calculated using the transfer matrix method. The influence of applied electric and laser fields on the electronic distribution is investigated. In studied systems, a laser‐induced attenuation for anomalous electric polarization of the excited state is found. Also, an oscillator strength increasing under high‐frequency laser radiation is obtained. The results presented in this article can be useful for novel device applications based on the intersubband transitions of electrons. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Charge‐transfer transitions and optic spectra of chromites: A model computation

In the cluster approach, we consider the peculiarities of charge‐transfer (CT) states and CT O 2p → Cr 3d transitions in the octahedral (CrO₆)^9? complex. We have computed the reduced matrix elements of electric‐dipole transition operator on many‐electron wave functions — the initial and final states of CT transitions. We have parameterized the obtained results and computed the relative intensities of various allowed CT transitions in the absence of the mixing of CT configurations having the same symmetry. Using the Tanabe‐Sugano technique, we have taken into account this mixing and obtained the energies of many‐electron CT transitions and their actual intensities as well. We have also allowed for the Coulomb interaction between the 2p‐electrons of the O^2? ligands and the 3d‐electrons of the central Cr³⁺ ion in the (CrO₆)^9? cluster. This interaction proved insignificant for the optic spectra. Modeling the optic spectrum of chromium‐based oxides has yielded a complicated CT band consisting of 33 lines with the main maximum at about 7 eV and satellites in the range of 4–5 and 8–9 eV. The total extent of the CT band is about 8 eV. The model spectrum is in satisfactory agreement with experimental data, which shows the limited validity of the generally accepted notion of a simple structure of CT spectra. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The nature of the transitions comprising the optical absorption spectra of solvated electrons

The theory of photoejection spectra of molecular anions is adapted for application to analyses of optical absorption data of solvated electrons in a number of different solvents. The results obtained generally support the identification of solvated electron optical absorption spectra entirely as bands of bound-to-continuum transitions and not as bound-to-bound transitions. Analyses of the absorbance behavior near the threshold for absorption lead to the conclusion that the solvated electron ground state deviates appreciably from spherical symmetry. Alternatively, the solvated electron ground state in ND₃ may be nearly spherically symmetric with a thermally accessible excited state of lower symmetry.     

Singlet-singlet electron transitions in isoelectronic monosubstituted benzenes. a semi-empirical study by a modified CNDO—CI method

A modified CNDO-CI method is presented which assigns the singly excited singlet configurations to the different irreducible representations and separately diagonalizes the resulting blocks in the Hamiltonian CI matrix, using the same number of effectively interacting terms for each irreducible representation (annihilation of interaction terms by the ZDO approximation being duly taken into account).Parameterization has been adjusted to fit a set of 25 experimentally well established O-O transition energies of different monocyclic compounds and the method has been applied to the first four transitions of the isoelectronic set of toluene, aniline, phenol and fluorobenzene.Attention has been paid to changes in dipole moments and in electron charge distributions, using population analysis and electron density maps, after suitable deorthogonalization of the bond order matrix.     

A study of crystalline transitions in a thermoplastic polyimide

A new polyimide derived from 4,4′-isophthaloyldiphthalic anhydride (IDPA) and 1,3-bis(4-aminophenoxy-4′-benzoyl)benzene (1,3-BABB) having semicrystalline behavior was prepared at NASA Langley Research Center in 1987. The crystalline transitions of this thermoplastic polyimide have been studied. The differential scanning calorimetry (DSC) pattern of partially imidized film exhibited two distinct crystalline melt endotherms. For this study each crystalline phase was isolated and enhanced by controlled thermal treatment. A film containing approximately 50% of both phases and an amorphous film were also prepared. Evaluations of these films were performed by DSC, wide-angle x-ray scattering (WAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Three distinct crystalline morphologies; ellipsoid, cubic, and needlelike embedded in an amorphous matrix were observed as a function of various cure conditions by SEM.     

Crystal field theory treatment of S2 ion impurity centres with Oh, D4h, C4v and C2v symmetry in alkali halides

The effect of impurity anions on the electron transitions in alkali halide phosphors has been studied. The energies of electron transitions have been calculated for O_h, D_4h, C_4v and C_2v symmetries in the cases of strong and weak fields. The theoretical model has been shown to agree satisfactorily with experimental data assuming the formation of higher symmetry impurity centres to be more probable.     

Single‐Molecule Spectroscopy on a Ladder‐Type Conjugated Polymer: Electron–Phonon Coupling and Spectral Diffusion

We employ low‐temperature single‐molecule spectroscopy combined with pattern recognition techniques for data analysis on a methyl‐substituted ladder‐type poly(para‐phenylene) (MeLPPP) to investigate the electron–phonon coupling to low‐energy vibrational modes as well as the origin of the strong spectral diffusion processes observed for this conjugated polymer. The results indicate weak electron–phonon coupling to low‐frequency vibrations of the surrounding matrix of the chromophores, and that low‐energy intrachain vibrations of the conjugated backbone do not couple to the electronic transitions of MeLPPP at low temperatures. Furthermore, these findings suggest that the main line‐broadening mechanism of the zero‐phonon lines of MeLPPP is fast, unresolved spectral diffusion, which arises from conformational fluctuations of the side groups attached to the MeLPPP backbone as well as of the surrounding host material.     

Observation of inner-shell triplet states of CO2 and N2O and of inner-shell fine structure in Kr and Xe

Inner-shell singlet-triplet transitions in CO₂ and N₂O have been observed by the electron energy-loss technique at low values of the incident electron energy, typically 1.4 times the excitation energies of the states. The same technique has been used to observe fine structure in transitions near the M_4.5 edges in Kr and the N_4.5 edges in Xe.     

Condensed heterocycles with a thiazole ring. 2. Monomethylidynecyanine dyes of the thiazolo[3,4-a]pyrimidine series

Unsymmetrical monomethylidynecyanine dyes that contain benzothiazole or quinoline residues were obtained on the basis of thiazolopyrimidine. The energies of the transitions and the electron distributions in the ground, first, and second excited states were calculated for several of the dyes obtained and for model compounds by the self-consistent-field configuration-interaction (SCF CI) method in order to interpret the first absorption bands and determine the localization of the electron transitions.See [1] for communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 639–643, May, 1982.     

镧系元素f-f跃迁光谱计算

运用不可约张量算符方法,建立了f-f超灵敏跃迁光谱的计算模型,编制了计算f离子^2s+1L~J能级、约化矩阵元、晶体场Stark能级、晶体场态-态跃迁振子强度及模拟吸收光谱的计算机程序.其中,自由f离子能级计算采用包括双电子与叁电子组态相互作用的二三参数模型,晶体场Stark分裂计算采用单电子轨道近似,用Newman角叠加模型计算晶体场参数.f-f跃迁振子强度计算包括静电诱导偶极跃、配体极化偶极跃、振动诱导电偶极跃迁及磁偶极跃迁的贡献.     

The Auger electron spectrum of water vapour

The Auger electron spectrum of water vapour has been recorded and analyzed. For the analysis, an approximate formula for calculating the intensities of the Auger electron lines is derived. It is shown, that the calculated intensities along with theoretical energies of the Auger transitions account well for the observed spectrum. In particular, new assignments in terms of transitions to triplet final states are suggested.     

Anwendung der quantitativen Augerelektronenspektroskopie (AES) auf dünne Oberflächenschichten

Zusammenfassung Die Grundgleichungen der quantitativen Auger-Elektronenspektroskopie werden auf dünne, homogene Schichten angewendet und am Beispiel einer Sn-Segregationsschicht auf einer Cu(111)-Oberfläche durch Vergleich mit Ergebnissen der Beugung niederenergetischer Elektronen (LEED) überprüft. Durch Variation der Oberflächenbelegung ist es möglich, das Verhältnis der mittleren freien Weglängen der Augerelektronen aus Augerübergängen verschiedener Energien des Matrixelements unmittelbar zu erhalten.

---

Application of quantitative Auger electron spectroscopy (AES) to thin surface layers

Summary The basic equations of quantitative Auger electron spectroscopy are applied to thin, homogeneous layers and are examined with reference to the example of a Sn segregation layer on a Cu(III) surface by comparison with the results for the diffraction of low-energy electrons (LEED). By variation of the surface coverage it is possible to obtain directly the ratio of the mean free parts of the Auger electron from Auger transitions of various energies of the matrix element.

     

Tests of semiclassical treatments of vibrational-translational energy transfer collinear collisions of helium with hydrogen molecules

Three kinds of semiclassical theory are tested against quantum mechanical results for vibrational transition probabilities and average vibrational energy transfers in collinear collisions of atoms with harmonic and Morse vibrators for the He-H₂ mass combination. The interaction potential is assumed to be a repulsive exponential function with an exponential parameter which is realistic for He-H₂ collisions. The energy range studied is total energies of 2–8 in units of ?ω_e. The uniform semiclassical approximations of classical S matrix theory are tested only for classically allowed transitions, i.e., for transition probabilities greater than about 0.2. They are accurate quantitatively for both harmonic and Morse vibrators. The integral expressions of classical S matrix theory are found to be quantitatively accurate for classically allowed and weakly classically forbidden transitions, i.e., for transition probabilities greater than about 0.01–0.05, and to be unreliable for strongly classically forbidden transitions. Quasiclassical trajectory methods yield qualitatively accurate results only for classically allowed transitions but the phase-averaged energy transfer in quasiclassical collisions may be accurate even when classically forbidden transition probabilities are important for the calculation of the average energy transfer. Forced quantum oscillator methods using a classical path whose initial velocity is the average of the initial and final velocities corresponding to the transition of interest are accurate for transition probabilities as small as 4 × 10^?8 for harmonic vibrators but do not seem to accurately account for the effect of anharmonicity.     

Modeling interband transitions in silver nanoparticle-fluoropolymer composites

The interband transition contributions to the optical properties of silver nanoparticles in fluoropolymer matrices are investigated. For the materials in this study, nanoparticle synthesis within the existing polymer matrix is accomplished using an infusion process that consists of diffusing an organometallic precursor gas into the free volume of the fluoropolymer and decomposing the precursor followed by metal nanoparticle nucleation and growth. The resulting polymer matrix nanocomposite has optical properties that are dominated by the response of the nanoparticles owing to the broadbanded transparency of the fluoropolymer matrix. The optical properties of these composites are compared to Maxwell-Garnett and Mie theory with results indicating that interband transitions excited in the silver nanoparticles affect the optical absorption over a range of frequencies including the surface plasmon resonance. It is shown that calculations of the optical absorption spectrum using published data for the silver dielectric function do not accurately describe the measured material response and that a classical model for bound and free electron behavior can best be used to represent the dielectric function of silver.     

Shallow and deep trap states of solvated electrons in methanol and their formation,electronic excitation,and relaxation dynamics

We present condensed-phase first-principles molecular dynamics simulations to elucidate the presence of different electron trapping sites in liquid methanol and their roles in the formation, electronic transitions, and relaxation of solvated electrons (e_met⁻) in methanol. Excess electrons injected into liquid methanol are most likely trapped by methyl groups, but rapidly diffuse to more stable trapping sites with dangling OH bonds. After localization at the sites with one free OH bond (1OH trapping sites), reorientation of other methanol molecules increases the OH coordination number and the trap depth, and ultimately four OH bonds become coordinated with the excess electrons under thermal conditions. The simulation identified four distinct trapping states with different OH coordination numbers. The simulation results also revealed that electronic transitions of e_met⁻ are primarily due to charge transfer between electron trapping sites (cavities) formed by OH and methyl groups, and that these transitions differ from hydrogenic electronic transitions involving aqueous solvated electrons (e_aq⁻). Such charge transfer also explains the alkyl-chain-length dependence of the photoabsorption peak wavelength and the excited-state lifetime of solvated electrons in primary alcohols.

Condensed-phase first-principles molecular dynamics simulations elucidate the presence of different electron trapping sites in liquid methanol and their roles in the formation, electronic transitions, and relaxation of solvated electrons.     

Theoretical investigation of charge transfer excitation and charge recombination in acenaphthylene–tetracyanoethylene complex

Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge‐balanced electron donor–acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor–acceptor complex was obtained by the second‐order Møller–Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor–acceptor complex in this work reveals that the S₁ and S₂ states of the electron donor–acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S₀ → S₁ and S₀ → S₂ transitions arise from π–π* excitations. The charge recombination in the ion pair complex will produce the charge‐balanced ground state or excited triplet state. According to the generalized Mulliken–Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2‐dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23–35, 2003