An application of second-order n-electron valence state perturbation theory to the calculation of excited states

n–electron valence state perturbation theory (NEVPT) is a form of multireference perturbation theory where all the zero-order wave functions are of multireference nature, being generated as eigenfunctions of a two–electron model Hamiltonian. The absence of intruder states makes NEVPT an interesting choice for the calculation of electronically excited states. Test calculations have been performed on several valence and Rydberg transitions for the formaldehyde and acetone molecules; the results are in good accordance with the best calculations and with the existing experimental data.Contribution to the Jacopo Tomasi Honorary Issue     

Theory of bridge-assisted electron transfer in systems with an intermediate link at high temperatures

From solution of the time-dependent wave equation by specifying the (t) function in the form of a linear combination a_i(t)_i+a_d(t)_d+a_j(t)_j (_i, _d, _j are the wave functions corresponding to localization of the electron on the donor, the intermediate link, and the acceptor), we obtain an expression for the electron transfer probability in a system consisting of six components: one direct transfer and five interference components. We have studied the effect of electronic structure and vibrational motion of the components of the system on the probability components. This has allowed us to find the dependence of the electron transfer probability on the ionization potential or the electron affinity of the intermediate link, playing the role of a catalyst or inhibitor of the process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 134–142, March–April, 1989.     

The electrochemical behavior ofortho-nitroanilides in an aprotic medium

Electrochemical reduction ofortho-nitroanilides in an aprotic medium has been studied by polarography and ESR. It has been shown that nitroanilide anion-radicals are formed at the first reduction wave potentials. The transfer of a second electron is accompanied by subsequent reactions (autoprotonation and homogeneous electron transfer), which occur in the bulk of the solution and lead to fairly stable intermediate anion-radicals ofortho-compounds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1067–1070, June, 1993.     

Electrochemical and spectroelectrochemical properties of manganese reconstituted myoglobin

Electrochemical and spectroelectrochemical properties of manganese(III) reconstituted myoglobin (Mn(III)–Mb) have been investigated. No redox wave of Mn(III)–Mb was observed at a highly hydrophilic indium oxide electrode on which rapid direct electron transfer of native myoglobin took place, suggesting the electron transfer reaction of Mn(III)–Mb at an indium oxide electrode is very slow. The rate constant of the chemical reduction of Mn(III)–Mb with dithionite was ca. 20 times smaller than that of native Mb. Using an optically transparent thin layer electrode (OTTLE) cell and Oxazine-170 perchlorate, 5,9-bis(diethylamino)-10-methyl-benzo[a]phenoxazonium perchlorate, as an electron transfer mediator, the redox potential for the Mn(III) Mn(II)–Mb couple was estimated to be −0.32 V versus Ag AgCl (sat. KCl) at 25°C.     

Molecular resistivities in organic polyenic wires: I. A one-dimensional photoconduction charge transfer model

In the present work we have developed a one-dimensional photoconduction charge transfer model, which allows us to determine the resistivities associated to π-conduction molecular channels of organic polyenic wires. In order to calculate the charge transmission coefficient through the conductor molecular wire, our model is based on the scattering process of electrons in metals according to Landauer's one-dimensional conductor approach. This model can be applied to those D–bridge–A molecular systems, constituted by an electron-donor group (D), an electron-acceptor group (A) and a polyenic conductor molecular bridge, which present a photoinduced charge transfer absorption band. According to the present model, molecular resistivities and resistances in the charge transfer excited state of a series of polyenic compounds containing several kinds of electron-donor groups and CO, as an electron-acceptor group, have been calculated by means of the INDO/S-CI method, in the framework of ZINDO semiempirical molecular orbital theory. The calculations allow us to determine the linear and nonlinear contributions to the total molecular resistance of the π-conduction channel in the charge transfer excited state. Linear resistivities for a series of polyenic aldehydes substituted by an electron-donor group (D=–CH₃, –OCH₃, –NH₂ and –N[CH₃]₂) range between 18 and 42 μΩ cm and these results agree with the order of magnitude expected in classic conductors such as metals, nonmetals, and doped polyacetylenic compounds in the ground state.     

Electron transfer theory in systems with an intermediate unit according to a bridge mechanism

We have obtained the component rates for direct and indirect transfer of an electron in a donor-intermediate unit-acceptor system located in a condensed medium using a formula determined from solving the time-dependent wave equation by the variational method. The time-dependent wave function was specified as a linear combination of functions corresponding to localization of the electron in the component parts of the system.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 524–532, September–October 1986.     

Effects of Configurational Fluctuation on Electronic Coupling for Charge Transfer Dynamics

We advance a theory for the effects of bridge configurational fluctuations on the electronic coupling for electron transfer reactions in donor-bridge-acceptor systems. The theory of radiationless transitions was applied for activationless electron transfer, where the nuclear Franck–Condon constraints are minimized, with the initial vibronic state interacting directly with the final vibronic manifold, without the need for thermal activation. Invoking the assumption of energy-independent coupling, the time-dependent initial state population probability was analyzed in terms of a cumulant expansion. Two limiting situations were distinguished, i.e. the fast configurational fluctuation limit, where the electron transfer rate is given in terms of the configurational average of me squared electronic coupling, and the slow configurational fluctuation limit, where the dynamics is determined by a configurational averaging over a static distribution of electron transfer probability densities. The correlation times for configurational fluctuations of the electronic coupling will be obtained from the analysis of molecular dynamics, in conjunction with quantum mechanical calculations of the electronic coupling, to establish the appropriate limit for electron transfer dynamics.     

Phototransfer of an electron in frozen solutions of cyanine dyes

The irradiation of frozen vitreous solutions of cyanine dyes in the absorption band of the quinoline fragment of the dye molecule leads to the two-quantum phototransfer of an electron from the pigment to the acceptor. The intermediate stages of the charge separation involve the transfer of electronic excitation energy from the quinoline fragment to the dye molecule as a whole. The transfer to the acceptor from a molecule of the dye in the monomeric state is more than 12 times as effective as the transfer of an electron from the dye in an associated state (reckoned for a single molecule in the aggregate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1734–1737, August, 1990.     

Configuration interactions with molecular orbitals from the SCF Xα scattered-wave approximation

A method has been devised for calculating the state energies and wave functions for molecules, with computer algorithms and implementation programs. Molecular integrals can be determined in an orbital basis by the X-SW method and can be used in programs based on nonempirical methods, which serve to extend the X. method. Estimates have been made of the state energies with correction for electron correlation for titanium and zirconium monofluorides.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 2, pp. 137–142, March–April, 1990.     

Theoretical analysis of electron-transfer crossover reactions between complex ions. Communication 4. Reactions involving ethylenediamine complexes of cobalt and ruthenium

Conclusions Calculations have been made within the bounds of the quantum-mechanical theory of chemical reactions of the rate constants and activation enthalpies of a number of electron transfer reactions involving the ethylenediamine complexes of cobalt and ruthenium. An estimate has been obtained of the inner-sphere reorganization energy for the Co(en)₃ ^3+/2+ complexes. The transmission coefficients for electron transfer in redox systems incorporating ethylenediamine complexes of cobalt and ruthenium have been compared, which enables a conclusion to be drawn on the degree of transferred-electron delocalization in the complexes being compared.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 353–358, February, 1984.     

Thermodynamic and kinetic characteristics of one-electron transfer reactions in N-alkylaniline-tetracyanoethylene charge transfer complex systems

One-electron transfer reactions in systems containing an N,N-dialkylaniline (D) and tetracyanoethylene (A) in methylene chloride proceed through the formation of AD and AD₂ charge transfer complexes. The tetracyanoethylene -system and nitrogen unshared electron pair of the N,N-dialkylaniline participate in the formation of the charge transfer complex. The equilibrium constants for complex formation K and rates of formation of the TCE^– radical-anions k were determined for this reaction. The sign of the regression coefficient in the correlation between the thermodynamic (K) and kinetic indices (k) for the one-electron transfer reactions in charge transfer complex systems indicates the formation of shortlived intermediates between the starting compounds and final Reaction products (in the case of increasing K(AD) values with increasing k(TCE^–)) or of several longlived intermediate complexes (in the case of increasing K(AD) values with decreasing k(TCE^–).Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 23, No. 6, pp. 692–699, November–December, 1987.     

Quenching of the fluorescence of riboflavin by the histidinates and alaninates of nickel,copper, and zinc

The formation of complexes of histidinates and alaninates of Ni(II), Cu(II), and Zn(II) with riboflavin (RF) in the ground state and the quenching of the fluorescence of RF by these compounds has been investigated. It has been found that the quenching of the fluorescence of RF by the Cu²⁺ and Ni²⁺ complexes is caused mainly by the nonemissive energy transfer from the donor (RF) to the metal ions. In the case of the Cu²⁺, Ni²⁺, and Zn²⁺ histidinates the formation of nonfluorescing unstable complexes (K_stab — 3–10) of the metal histidinates with RF in the ground state also contribute to the quenching. Free histidine and zinc histidinate quench the fluorescence of RF by the transfer of an electron to the excited molecule of the flavin with the formation of nonfluorescing reduced RF.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 488–493, July–August, 1985.     

Dynamic Pumping of Elementary Charge Transfer by Environmental Dissipative Reorganization

The nature of elementary charge (electron) transfer in condensed media is interpreted in terms of the uncertainty relation. The emergence of a pure (quantum-mechanical) state of an electron transfer is examined for two complementary cases: the electron transfer state is defined by the interaction between the electron and its environment through a spontaneous pumping of this state by either ordered or disordered motion of the environment. The latter case corresponds to either adiabatic or nonadiabatic electron transfer of the Landau–Zener type. The former case was discovered by the author and is employed for explaining the origin of intensive narrow optical bands.     

Effects of Electron Correlations in a Simple Model for Adiabatic Electrochemical Reactions: The Diagram of Kinetic Regimes

In the framework of the surface-molecule model for adiabatic electrochemical reactions of electron transfer previously suggested by the authors, a diagram of kinetic regimes (DKM) in the space of model parameters is obtained. The diagram comprises critical regions that correspond to various feasible electron transfer processes (transfer of one electron, simultaneous transfer of two electrons, transfer of two electrons in the presence of an intermediate state) and a region corresponding to electroadsorption of the reagent in certain charge states. Analytical expressions for boundary curves of DKM are obtained for a number of simple cases. A DKM for the general case of the surface-molecule model with an exact allowance for electron–electron correlations is constructed and analyzed.     

Single-center method of calculation for clusters and molecules other than hydrides

A new single-center method is proposed for solving the one-particle Schrödinger equation for molecules other than hydrides and for clusters, based on the method of associated differential and integral equations. The higher terms of the expansion of the wave function of the electron are replaced by linear combinations of analytical functions. This reduces the system of integro-differential equations to a system of differential and algebraic equations, for which stable numerical solutions have been worked out. Calculations are given of the energy and functions of the 2s state of an oxygen atom with a displaced center.Translated from Teoreticheskaya i Éksperimental'naya Khimiya,Vol. 25, No. 1, pp. 12–20, January–February, 1989.The authors are grateful to A. G. Kochur for making available the program for the SC expansion of atomic functions, and also to V. L. Sukhorukov for discussing the results.     

Optimal Kinoshita wave functions for heliumlike atoms

An extensive optimization has been performed for the composition ofN terms, as well as the exponent and the mixing coefficients, of Kinoshita wave functions for heliumlike atoms with atomic numberZ. The optimalN-term Kinoshita functions have been constructed forN=1–10, 20, 30, 40, 50, 100 andZ=1(H^–)–10(Ne⁸⁺). The present results demonstrate that the optimal term selection dramatically improves the accuracy of the Kinoshita function: In the case of He, for example, the optimal 100-term Kinoshita function gives – 2.903 724 376 95 hartrees, which is only 8×10^–11 hartrees higher than the most accurate literature value.     

Electron correlation and bond-length alternation in polyene chains

The PPP model is used to consider polyene chains in the ground state with allowance for the interaction of the electrons with core deformations. The stationary wave functions describing the electron correlations are derived as antisymmetrized products of two-electron functions optimized with respect to all variational parameters. The bond-length alternation can be related to the characteristics of the electron-electron potential; one can allow approximately for the effects of interaction between electrons at adjacent centers on the alternation by renormalizing the parameters in the Hubbard model.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 263–270, May–June, 1986.In am indebted to I. I. Ukrainskii for a discussion of this.     

Influence of the protein medium on the electronic state and electron transfer in metalloproteins

On the basis of a semicontinuum method, considering the influence of the heme structure and the polarization of the protein macromolecule, the energy and wave functions of the electron on the active site of cyt C were calculated for the stype ground and excited states. The reorganization energy, matrical element, and rate of electron transfer in the self-exchange reaction of cyt C were calculated. The results are in satisfactory agreement with the experimental data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 180–183, March–April, 1992.The author would like to express gratitude to V. D. Lakhno for a useful discussion of the work and to R. R. Gabdullin for providing the program for calculating the electronic states.     

Solubility of methane in aqueous solutions of triethylenediamine

The solubilities of methane were measured in water and aqueous solutions of triethylenediamine (TED), triethylenediamine hydrochloride (TED·HCl), and HCl at several concentrations up to 1M at 5° intervals from 5 to 25°C. Methane solubilities in solutions of TED·HCl and HCl are lower than those in water and decrease with increasing cosolute concentration. In contrast, the solubilities in TED solutions are greater than those in water and increase with increasing TED concentration. The order of methane solubilities at 25°C in water and in 0.5M aqueous solutions is TED>H₂O>HCl>TED·HCl with Ostwald coefficients of 3.57×10^–2, 3.44×10^–2, 3.26×10^–2, and 3.19×10^–2, respectively, and with an experimental precision of about ±0.2×10^–3. Thermodynamic functions for the transfer of methane from water to 0.25, 0.50, and 0.75M aqueous solutions have been calculated on the molar concentration scale. The free energies of transfer are compared with previous results for methane in aqueous solutions of tetraalkylammonium halides.