Nonradiative Charge Transfer Research Articles

Nonradiative charge transfer in collisions of protons with rubidium atoms

The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10−3 keV–10 keV. The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region. The importance of rotational coupling for chargetransfer process is stressed. Compared with the radiative charge-transfer process, nonradiative charge transfer is a dominant mechanism at energies above 15 eV. The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail. The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

Low-energy charge transfer in collisions of He2+with H in a Debye plasma

Charge transfer in collisions of $\ensuremath{\alpha}$ particles with ground-state H embedded in a Debye plasma is studied in the low-energy region from $10$${}^{\ensuremath{-}4}$ eV to $5$ keV. The screened Coulomb interaction is described by the Debye-H\"uckel potential. The relevant molecular potentials and coupling matrix elements are obtained using a modified multireference single-and double-excitation configuration interaction package. Total and state-selective cross sections in the nonradiative charge-transfer collisions from $60$ eV to $5$ keV are calculated using the quantum-mechanical molecular-orbital close-coupling method. Both optical-potential and semiclassical methods have been used in the investigation of the radiative charge transfer from $10$${}^{\ensuremath{-}4}$ to $1$ eV and $1$ to $10$${}^{2}$ eV, respectively. The total cross sections for the no-screening case are in good agreement with the existing data. The effects of the screened Coulomb potential on the electron-capture cross sections are discussed.

ChemInform Abstract: Absorption and Fluorescence of Pyrylium Salts.

Absorption and fluorescence of donor-substituted pyrylium compounds are studied in order to get information of the x- and y-chromophore system and of the role of structural and solvent effects. The experimental results are in accordance with the assumption that the absorption and fluorescence behaviour can be rationalized in terms of intramolecular radiative and non-radiative charge transfer (charge shift) processes.

Radiative and nonradiative charge transfer in collisions ofBe2+andB3+ions with H atoms

The nonradiative charge-transfer processes in Be{sup 2+}(1s{sup 2})+H(1s) and B{sup 3+}(1s{sup 2})+H(1s) collisions are investigated by the quantal molecular orbital close-coupling method in the energy range of 10{sup -5}eV/u-10 keV/u and by the two-center atomic-orbital close-coupling method in the energy range of 0.1-100 keV/u. The radiative charge-transfer cross sections are calculated by using the optical potential and semiclassical methods in the energy range 10{sup -5}-100 eV/u. For both collision systems, the nonradiative charge-transfer cross sections in the low-energy region show an increasing behavior with decreasing energy. The nonradiative process is the dominant charge-transfer process in the Be{sup 2+}(1s{sup 2})+H(1s) collision in the entire eV and sub-eV energy region. In the B{sup 3+}(1s{sup 2})+H(1s) collision case, however, the cross section for radiative decay to 1 {sup 2{Sigma}+} and 2 {sup 2{Sigma}+} molecular states significantly exceeds that for the nonradiative process for energies below 30 eV/u.

Radiative charge transfer and radiative association in He++Ne collisions

A fully quantum-mechanical approach is utilized to study the collision process of He${}^{+}$ with neutral neon, and the radiative charge transfer (RCT) and radiative association (RA) cross sections are presented in the energy range from 0.08 meV to 1 eV, while the optical potential and semiclassical methods are adopted to calculate the total radiative decay cross sections for energies from 0.08 meV to 5 keV. The potential energy curves and dipole transition matrix elements are obtained by an ab initio multireference configuration interaction package. For the related three lowest $X$ ${}^{2}{\ensuremath{\Sigma}}^{+}$, $A$ ${}^{2}\ensuremath{\Pi}$, and $B$ ${}^{2}{\ensuremath{\Sigma}}^{+}$ states, the spectroscopic data are in good agreement with other theoretical calculations and experimental measurements. Our results indicate that the RCT cross section is much larger than the nonradiative charge transfer cross section for collision energy $E$ $<$ 20 eV, and when $E$ $>$ 40 eV, the nonradiative process becomes dominant. Especially, we found that in the present collision system the RA process is more important than the RCT process when $E$ $<$ 1 meV. The RCT and RA rate coefficients are also given for temperatures from 1 to 4 $\ifmmode\times\else\texttimes\fi{}{10}^{3}$ K.

Accurate calculations of the ground state and low-lying excited states of the (RbBa)+ molecular ion: a proposed system for ultracold reactive collisions

Collisions of ultracold Ba+ ions on a Rb Bose–Einstein condensate have been suggested as a possible benchmark system for ultracold ion-neutral collision experiments. However, a priori knowledge of the possible processes is desirable. For this purpose, we here present high-level four-component coupled cluster and multi-reference configuration interaction calculations of potential energy curves, dipole moments and spectroscopic constants of the experimentally interesting low-lying electronic states of the (RbBa)+ molecule. Our results show significant avoided crossings between the Rb + Ba+ entrance channels and low-lying charge transfer states of the Rb+ and Ba(3D) atomic channels, indicating that a fast non-radiative charge transfer is possible. Population analysis shows that a partially covalent polar bond is formed in the ground state, which thus deviates significantly from a pure Rb+ + Ba interaction. This finding is corroborated by the electric dipole moment which is found only to be 4.5 D at the equilibrium bond distance, compared with the 14 D for a pure Rb+ + Ba interaction, thereby supporting the view of a partial charge transfer between the two atoms.

Charge transfer and association of protons colliding with potassium from very low to intermediate energies

The nonradiative charge-transfer process for ${\mathrm{H}}^{+}+\mathrm{K}(4s)$ collision is investigated using the quantum-mechanical molecular-orbital close-coupling method for collision energies from $1$ eV to $10$ keV. The radiative-decay and radiative charge transfer cross sections are calculated using the optical potential approach and the fully quantal method, respectively, for the energy range of ${10}^{\ensuremath{-}5}$--$10$ eV. The radiative-association cross sections are obtained by subtracting the radiative charge-transfer part from total radiative-decay cross sections. The relevant molecular data are calculated from the multireference single- and double-excitation configuration interaction approach. The nonradiative charge transfer is the dominant mechanism at energies above $2$ eV, whereas the radiative charge transfer becomes primary in the low-energy region of $El1.5$ eV. The present radiative-decay cross sections disagree with the calculations of Watanabe et al. [Phys. Rev. A 66, 044701 (2002)]. The total charge-transfer rate coefficient is obtained in the temperature range of $1$--$20$$000$ K.

Radiative charge transfer in collisions ofH+with Na at very low energies

The radiative charge transfer for ${\text{H}}^{+}+\text{Na}(3s)$ collisions has been investigated by using both the optical-potential and semiclassical methods in the energy ranges of ${10}^{\ensuremath{-}6}--10$ and ${10}^{\ensuremath{-}2}--100\text{ }\text{eV}$, respectively, which are in agreement in the overlapping energy region. The relevant molecular potentials and dipole matrix elements were obtained from the multireference single- and double-excitation configuration interaction approach. The radiative charge-transfer cross sections display rich resonance structures, due to the formation of quasibound rotational-vibrational molecular states, in the energy range below 0.2 eV. The present radiative charge-transfer cross-section results disagree with the calculations of Watanabe et al. [Phys. Rev. A 66, 044701 (2002)]. The rate coefficient is obtained for temperatures between 0.1 and $20\text{ }000\text{ }\text{K}$. Below 7000 K, it has a nearly constant value of approximately $1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }{\text{cm}}^{3}\text{ }{\text{s}}^{\ensuremath{-}1}$, which is about 1/3 of that of Watanabe et al. The nonradiative charge transfer becomes dominant at energies above 4 eV.

Afterglow Suppression and Non-Radiative Charge-Transfer in CsI:Tl,Sm

Suppression of afterglow in co-doped CsI:Tl is found to be an order of magnitude more effective in CsI:Tl, Sm than in CsI:Tl, Eu. Rate equations predict that deep electron traps introduced by co-doping with samarium effectively scavenge electrons from shallow traps associated with thallium, thus suppressing afterglow in the time domain of tens of milliseconds. In addition, combined radioluminescence and thermoluminescence experiments suggest that electrons released by samarium recombine non-radiatively with trapped holes, thus providing a mechanism for suppression of hysteresis. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ab</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">initio</i> quantum chemistry calculations support the conclusion that non-radiative charge-transfer transitions in CsI:Tl, Sm are enabled by the presence of low-energy excited states of within the ground configuration.

Intramolecular exciplexes based on benzoxazole: photophysics and applications as fluorescent cation sensors

Exciplex behaviour of three benzoxazole derivatives has been detected and intensively investigated by means of steady-state and time-resolved fluorescence techniques and transient absorption spectroscopy. The fluorescence of these compounds shows the properties which are typical for the excited state charge transfer complexes (exciplexes). Besides of the short wavelength fluorescence, which is similar in spectral distribution to the fluorescence of the electron acceptor (2-p-tolyl-benzoxazole), the red shifted, broad and structureless emission band is observed in solvents of low and medium polarity. The detailed analysis of the fluorescence data shows that the ratio of the CT and LE fluorescence initially increases with increasing solvent polarity, achieves a maximum, and drops for more polar solvents (epsilon(s) = 7). Similar behaviour is observed for the exciplex fluorescence lifetimes. The overall fluorescence and the relative intersystem crossing quantum yields show the decrease of these values with increasing solvent polarity. These observations have been explained on the basis of Marcus-type theory for nonradiative charge transfer rate constants. Increasing solvent polarity strongly accelerates the back electron transfer process which recovers the whole molecule in the ground state. The probability of the compact exciplex formation (i.e. sandwich-type structures) depends on solvent viscosity and degree of freedom of the bending of the saturated linker. The compound containing crown ether as a donor subunit may be used as a fluorescent indicator of inorganic cations (barium and lithium). We found an effective complexation of the compound in the ground state with barium and lithium cations. The complex is also stable in the excited state which manifests itself in strong increase of the fluorescence intensity.

The influence of intramolecular charge redistribution at the photoexcitation stage on the rate of subsequent electron transfer

The two-stage model of photoinduced electron transfer includes an explicit description of photoexcitation and nonradiative charge transfer. The model takes into account intramolecular reorganization and Coulomb interaction between the electron being transferred and medium polarization fluctuations. We studied the influence of intramolecular electron density redistribution on the rate of photoinduced electron transfer in donor-acceptor complexes. Excitation pulse frequency and donor dipole moment variations in the excited state changed the nonthermal and thermal electron transfer rates by 2–3 orders of magnitude.

Tunable energy transfer between [formula omitted] luminescent nanoclusters and rare earth ions in aqueous solution

Energy transfer has been studied between dicyanoaurate(I) luminescent nanocluster donor ions and Tb 3+ and Eu 3+ acceptor ions in aqueous solutions with steady-state luminescence at room temperature. The f–f transition emission intensities of Tb 3+ ions can be sensitized and enhanced by varying the dicyanoaurate(I) donor ion’s concentration, due to the formation of different excimer and exciplex nanoclusters. However, the f–f transition emission intensities of Eu 3+ ions are not enhanced but the donor’s emission is quenched thorough a non-radiative charge transfer pathway. The Stern–Völmer constants show different quenching efficiencies for different nanoclusters of the donor.

External Electric Field Effects on State Energy and Photoexcitation Dynamics of Diphenylpolyenes

External electric field effects on state energy and photoexcitation dynamics have been examined for para-substituted and unsubstituted all-trans-diphenylpolyenes doped in a film, based on the steady-state and picosecond time-resolved measurements of the field effects on absorption and fluorescence. The substitution dependence of the electroabsorption spectra shows that the dipole moment of the substituted stilbene in the Franck-Condon excited state becomes larger with increasing difference between the Hammet constants of the substituents. Fluorescence quantum yields of 4-(dimethylamino)-4'-nitrostilbene and 4-(dimethylamino)-4'-nitrodiphenylbutadiene are markedly reduced by an electric field, suggesting that the rates of the intramolecular charge transfer (CT) from the fluorescent state to the nonradiative CT state are accelerated by an external electric field. The magnitude of the field-induced decrease in fluorescence lifetime has been evaluated. The isomerization of the unsubstituted all-trans-diphenylpolyenes to the cis forms is shown to be a significant nonradiative pathway even in a film. Field-induced quenching of their fluorescence as well as field-induced decrease in fluorescence lifetime suggests that the trans to cis photoisomerization is enhanced by an electric field.

Surface Raman scattering studies on the adsorption of p-hydroxybenzoic acid at Au electrodes with ultraviolet excitation

The potential-dependent surface Raman spectrum of adsorbed p-hydroxybenzoic acid (PHBA) on a roughened Au electrode has been obtained with ultraviolet excitation at 325 nm. The surface Raman spectra of PHBA are sensitive to the negative shift of potential and the electrode potential at which the resonance (potential of maximum intensity) occurs varies with the vibrational mode, indicating that the PHBA molecules are chemisorbed on the Au surface. A non-radiative charge transfer mechanism could probably explain the experiment results in the present work. The probable reasons are given.

Charge-transfer cross sections in collisions of ground-state Na atoms withH+at low-eV collision energies

Cross sections for nonradiative charge transfer in ${\mathrm{H}}^{+}+\mathrm{N}\mathrm{a}(3s)$ collisions at energies less than or equal to 40 eV have been calculated using a fully quantum-mechanical approach. The calculated cross sections agree well with the experimental data in the entire energy range, but do not agree with other calculations at low energies. We discuss possible causes of this difference. Using the calculated cross sections, the rate coefficients at temperatures below 20 000 K have been calculated, and compared with those of other theoretical calculations.

Ultrafast spectroscopy of dark states in solid state sexithiophene

Femtosecond time resolved photoinduced transmission studies are carried out in nanocrystalline dihexylsexithiophene films with long range structural order. The results are compared with those obtained for sexithiophene in several states of aggregation. We explain the lack of radiative recombination in the solid phase with the formation of two nonradiative excitations, dark excitons and charge transfer states. The dark exciton dynamics is studied in detail in dihexylsexithiophene films; thermalization occurs within 200 fs, then decay takes place by mutual annihilation in the first ps, and by monomolecular recombination at longer times. Optical dynamics indicates that within the pump pulse a second excitation is formed, and we assign it to charge transfer states. The latter decay monomolecularly in the hundred ps time scale.

Electron Transfer in Porphyrin Multimolecular Self-Organized Nanostructures

On the base of of covalent and non-covalent bonds nanoscale self-assembling multiporphyrin arrays with well-defined geometry, the controllable number of interacting components and their spectral and photophysical properties were formed. The deactivation of excited singlet and triplet states was studied using steady-state, time-resolved picosecond fluorescence (Δ½≈30 ps) and femtosecond pump-probe (Δ½≈280 fs) spectroscopy in solvents of various polarity at 77–300 K. It has been found that the competition between the non-radiative energy transfer (within ≤10 ps) and charge transfer (within 300 fs - 700 ps) processes in the systems depends on the structure, spectral and redox properties of interacting subunits and may be driven by the distance, temperature and solvent polarity. The possible pathways and mechanisms of the electron transfer in the systems of various types are discussed (Marcus theory for the “normal” region and the non-adiabatic case., the “superexchange” mechanism).

Errata: Radiative and Nonradiative Charge Transfer in Collisions of H + with Li below 1 keV

Errata: Radiative and Nonradiative Charge Transfer in Collisions of H + with Li below 1 keV

Energy Gap Law for Nonradiative and Radiative Charge Transfer in Isolated and in Solvated Supermolecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnergy Gap Law for Nonradiative and Radiative Charge Transfer in Isolated and in Solvated SupermoleculesM. Bixon, Joshua Jortner, J. Cortes, H. Heitele, and M. E. Michel-BeyerleCite this: J. Phys. Chem. 1994, 98, 30, 7289–7299Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/j100081a010RIGHTS & PERMISSIONSArticle Views2867Altmetric-Citations192LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Radiative and nonradiative charge transfer in collisions of H(+) with Li below 1 keV

Radiative and nonradiative charge transfer in collisions of H(+) with Li below 1 keV