Charge transfer collisions between fullerenes: C 60 3+ + C60

Charge transfer collisions between C ₆₀ ³⁺ and C₆₀ are studied for collision energies between 400 and 3600 eV. Single and double electron transfers are observed, both occuring under single collision conditions. Absolute charge transfer cross sections are determined as a function of collision energy. The cross section for single electron capture of approx. 300 Ų is about two times larger than that for double electron transfer. For both processes the cross section increases slightly with increasing collision energy.     

Scattering of low energy He2+ ions by Ne,Ar, and Kr atoms

Experimental studies of collisions of He²⁺ ions with Ne, Ar, and Kr atoms have been carried out at laboratory kinetic energies in the range 8 ? E₁ ? 10 eV. For each collision pair, relative differential cross sections for elastic scattering, and for the formation of He⁺ by single charge transfer [e.g., He²⁺ + R = He⁺ + (R⁺)^*] were measured. Information concerning the initial states of the charge transfer products was also obtained, from measurements of the kinetic energy distributions of the He⁺ + He = Ne⁺(2s 2p⁶²S) ± He⁺(²S), whereas for the other systems, transfer proceeds via a number of channels. The He⁺-ion kinetic energy measurements indicated that for He²⁺. Ar both Ar⁺ both Ar⁺ and Ar²⁺ are formed in transfer, and that for He²⁺, Kr only Kr²⁺ (and no Kr⁺) was formed.The differential elastic scattering patterns were analyzed by means of cross section calculations based on an approximate form of the optical model. These calculations indicated that the pronounced shoulders observed in the σ_el(θ) versus θ curves arose from scattering from an attractive potential well, in the presence of concurrent inelastic scattering. Using parametrized Morse potentials to represent the ground electronic states of (HeNe)²⁺, (HeAr)²⁺, and (HeKr)²⁺, the corresponding well-depth are estimated to be, respectively: 1.0 eV, 2.1 eV and 2.6 eV.     

Excitation and charge transfer in He++H collisions

For the conflictive case of He⁺+H collisions, we present a norm-method optimization of the parameters included in the (often used) two-electron translation factor of Errea et al. As surmised in a previous publication, a strong cut-off is needed at short internuclear distances to prevent the translation factor from marring the properities of the molecular expansion there. With a basis of 16 molecular states, we present the first calculations including translation factors, of total and partial charge exchange and excitation cross sections in He⁺+H collisions, as well as the alignment parameter A₂₀ for hydrogen excitation. Good agreement with experiment is reached up to the energy range where ionization and charge exchange cross sections are comparable.     

Excitation‐Wavelength‐Dependent,Ultrafast Photoinduced Electron Transfer in Bisferrocene/BF2‐Chelated‐Azadipyrromethene/Fullerene Tetrads

Donor–acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron‐transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor–acceptor dyads, revealing excitation‐wavelength‐dependent photochemical properties demands multimodular, photosynthetic‐reaction‐center model compounds. Here, we successfully demonstrate donor– acceptor excitation‐wavelength‐dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF₂‐chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured “closely” and “distantly” positioned donor–acceptor systems. The near‐IR‐emitting BF₂‐chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation‐wavelength‐dependent, photoinduced, electron‐transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc⁺–ADP–C₆₀^.? charge‐separated state upon C₆₀ excitation, and Fc⁺–ADP^.?–C₆₀ formation upon ADP excitation is demonstrated.     

A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in Modular Porphyrin–[10]CPP⊃Fullerene Complexes

Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non‐covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo‐[10]CPP is the key to the synthesis of a porphyrin–[10]CPP conjugate, which binds C₆₀, C₇₀, (C₆₀)₂, and other fullerenes (K_A>10⁵ m ^?1). Fluorescence and pump–probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge‐separated states. The advantage of this approach towards electron donor–acceptor dyads is evident in the case of dumbbell‐shaped (C₆₀)₂, which gave intricate charge‐transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross‐coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.     

Estimation of peptide N–Cα bond cleavage efficiency during MALDI‐ISD using a cyclic peptide

Matrix‐assisted laser desorption/ionization in‐source decay (MALDI‐ISD) induces N–C_α bond cleavage via hydrogen transfer from the matrix to the peptide backbone, which produces a c′/z? fragment pair. Subsequently, the z? generates z′ and [z + matrix] fragments via further radical reactions because of the low stability of the z?. In the present study, we investigated MALDI‐ISD of a cyclic peptide. The N–C_α bond cleavage in the cyclic peptide by MALDI‐ISD produced the hydrogen‐abundant peptide radical [M + 2H]⁺? with a radical site on the α‐carbon atom, which then reacted with the matrix to give [M + 3H]⁺ and [M + H + matrix]⁺. For 1,5‐diaminonaphthalene (1,5‐DAN) adducts with z fragments, post‐source decay of [M + H + 1,5‐DAN]⁺ generated from the cyclic peptide showed predominant loss of an amino acid with 1,5‐DAN. Additionally, MALDI‐ISD with Fourier transform‐ion cyclotron resonance mass spectrometry allowed for the detection of both [M + 3H]⁺ and [M + H]⁺ with two ¹³C atoms. These results strongly suggested that [M + 3H]⁺ and [M + H + 1,5‐DAN]⁺ were formed by N–C_α bond cleavage with further radical reactions. As a consequence, the cleavage efficiency of the N–C_α bond during MALDI‐ISD could be estimated by the ratio of the intensity of [M + H]⁺ and [M + 3H]⁺ in the Fourier transform‐ion cyclotron resonance spectrum. Because the reduction efficiency of a matrix for the cyclic peptide cyclo(Arg‐Gly‐Asp‐D‐Phe‐Val) was correlated to its tendency to cleave the N–C_α bond in linear peptides, the present method could allow the evaluation of the efficiency of N–C_α bond cleavage for MALDI matrix development. Copyright © 2016 John Wiley & Sons, Ltd.     

He++N2 Charge Transfer Reaction: An Ab initio Analysis

An ab initio analysis on the involved potential energy surfaces is presented for the investigation of the charge transfer mechanism for the He⁺+N₂ system. At high collision energy, as many as seven low-lying electronic states are observed to be involved in the charge transfer mechanism. Potential energy surfaces for these low-lying electronic states have been computed in the Jacobi scattering coordinates, applying multireference configuration interaction level of theory and aug-cc-pVQZ basis sets. Asymptotes for the ground and various excited states are assigned to mark the entrance (He⁺+N₂) and charge transfer channels (He+N₂⁺). Nonadiabatic coupling matrix elements and quasi-diabatic potential energy surfaces have been computed for all seven states to rationalize the available experimental data on the charge transfer processes and to facilitate dynamics studies.     

Charge exchange in C6+ + H (1s) collisions at low energies

The low‐energy single electron capture cross‐sections by C⁶⁺ from H atoms have been evaluated employing the semiclassical, impact parameter, close‐coupling method based on a molecular expansion augmented with the plane‐wave translation factor. Using the method of Bates and Carson, the exact Born–Oppenheimer eigenfunctions and eigenvalues are calculated. Eight‐state coupled equations are solved to obtain transition probabilities and thereby evaluate capture cross‐sections. Our calculated capture cross‐sections agree well with other theoretical and experimental results. At these energies it is found that the capture into the n = 4 manifold of the C⁵⁺ remains the main contributor to the charge exchange process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Charge transfer to helium ions from metastable helium

The cross section for charge transfer in He⁺He(2³S) collisions is calculated using the asymptotic theory of ion-atom interactions, including the effects of polarization and momentum transfer. The results agree well with recent measurements by the merged beam technique.     

On the mechanism of the He+ + N2 thermal energy dissociative charge transfer reaction

ICR spectroscopy has been used to reinvestigate the He⁺ + N₂ charge transfer reaction at thermal energies. It is concluded that at least 60% of the N⁺ come from short lived excited (N₂⁺)^*.     

Crossed beam study of He+-O2 charge transfer reactions in the collision energy range 0.5–200 eV

Energy spectra and angular distributions of the O⁺ and O ₂ ⁺ product ions resulting from the He⁺-O₂ charge transfer reaction have been measured in the collision energy range 0.5–200 eV using the crossed-beam method. The O ₂ ⁺ ions represent only a minor fraction of the reaction products (0.2–0.6% over the energy range measured). In the dissociative charge transfer reaction, four main processes are identified leading to O+O⁺ reaction products in different electronic states. Two different mechanisms can be distinguished, each being responsible for two of the observed processes:(i) a long-distance energy-resonant charge transfer process involving thec ⁴∑ _u ^? (v′=0) state of O ₂ ⁺ and(ii) a slightly exothermic charge transfer process via the (III)²∏ _u state of O ₂ ⁺ (with the exothermicity depending on the collision energy). Angle-integrated branching ratios and partial cross sections (in absolute units) have been determined. The branching ratios of the individual processes show a pronounced dependence on the collision energy. At low energies, the O⁺ product ions are preferentially formed in the² P ⁰ and² D ⁰ excited states. The angular distributions of the O⁺ product ions show an anisotropic behaviour indicating an orientation-dependent charge transfer probability in the He⁺ ?O₂ reaction.     

Differential scattering cross sections for collisions of alkali ions and atoms. II. Electronic excitation via rotational coupling in LiK+ and NaK+

Relative differential cross sections, for both direct and charge exchange scattering have been obtained for the Li⁺ + K, Na⁺ + K and K⁺ + Na alkali ion—atom collisions, over the energy range 200–1200 eV and for scattering angles 0–6 mrad (in one case 0–15 mrad)- The experimental results are compared to semiclassical calculations, based upon recent potential energy curves. The charge exchange probabilities are calculated by solving the time dependent Schrödinger equation in a two-state approximation. In the Li⁺+ K experiment diffraction effects are observed, which can be compared to the Fraunhofer diffraction. of an annular diaphragm.     

Double‐Oxygen‐Atom Transfer in Reactions of CemO2m+ (m=2–6) with C2H2

Cerium oxide cluster cations (Ce_mO_n⁺, m=2–16; n=2m, 2m±1 and 2m±2) are prepared by laser ablation and reacted with acetylene (C₂H₂) in a fast‐flow reactor. A time‐of‐flight mass spectrometer is used to detect the cluster distribution before and after the reactions. Reactions of stoichiometric Ce_mO_2m⁺ (m=2–6) with C₂H₂ produce Ce_mO_2m?2⁺ clusters, which indicates a “double‐oxygen‐atom transfer” reaction Ce_mO_2m⁺+C₂H₂→Ce_mO_2m?2⁺+(CHO)₂ (ethanedial). A single‐oxygen‐atom transfer reaction channel is also identified as Ce_mO_2m⁺+C₂H₂→Ce_mO_2m?1⁺+C₂H₂O (at least for m=2 and 3). Density functional theory calculations are performed to study reaction mechanisms of Ce₂O₄⁺+C₂H₂, and the calculated results confirm that both the single‐ and double‐oxygen‐atom transfer channels are thermodynamically and kinetically favourable.     

Molecular treatment of charge transfer cross sections in N5+ collisions with H2

We present cross sections for electron capture in N⁵⁺+H₂ collisions in the energy range 100 eV/amu≤E≤6 keV/amu. We employ a model potential aproximation to treat the interaction of the active electron with the cores, and a recently proposed method, which applies the independent particle model to evaluate the Hamiltonian matrix elements. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

A new phosphorescent heteroleptic cuprous complex with a neutral 2‐methylquinolin‐8‐ol ligand: synthesis,structure characterization,properties and TD–DFT calculations

Luminescent Cu^I complexes have emerged as promising substitutes for phosphorescent emitters based on Ir, Pt and Os due to their abundance and low cost. The title heteroleptic cuprous complex, [9,9‐dimethyl‐4,5‐bis(diphenylphosphanyl)‐9H‐xanthene‐κ²P ,P ](2‐methylquinolin‐8‐ol‐κ²N ,O )copper(I) hexafluorophosphate, [Cu(C₁₀H₉NO)(C₃₉H₃₂OP₂)]PF₆, conventionally abbreviated as [Cu(Xantphos)(8‐HOXQ)]PF₆, where Xantphos is the chelating diphosphine ligand 9,9‐dimethyl‐4,5‐bis(diphenylphosphanyl)‐9H‐xanthene and 8‐HOXQ is the N ,O‐chelating ligand 2‐methylquinolin‐8‐ol that remains protonated at the hydroxy O atom, is described. In this complex, the asymmetric unit consists of a hexafluorophosphate anion and a whole mononuclear cation, where the Cu^I atom is coordinated by two P atoms from the Xantphos ligand and by the N and O atoms from the 8‐HOXQ ligand, giving rise to a tetrahedral CuP₂NO coordination geometry. The electronic absorption and photoluminescence properties of this complex have been studied on as‐synthesized samples, whose purity had been determined by powder X‐ray diffraction. In the detailed TD–DFT (time‐dependent density functional theory) studies, the yellow emission appears to be derived from the inter‐ligand charge transfer and metal‐to‐ligand charge transfer (M +L ′)→LCT excited state (LCT is ligand charge transfer).     

Interaction of acetonitrile with alkaline metal cations: A density functional,coupled‐cluster,and quadratic configuration interaction study

A systematic quantum chemical study of CH₃CN and its CH₃CN?M⁺ 1:1 model adducts (M⁺∈{Li⁺, Na⁺}) is presented, with respect to binding energetics, structural and vibrational force field changes. Several gradient‐corrected density functional levels of theory were employed (of both “pure” and “hybrid” character), together with the coupled cluster including double substitutions from the Hartree–Fock determinant (CCD) and quadratic configuration interaction including single and double substitutions (QCISD) methods [with the rather large 6‐311G(d,p) basis set], and their performances compared. The binding energy decompositions according to the Kitaura–Morokuma scheme and the reduced variational space self‐consistent field (RVS‐SCF) method have shown that the electrostatic plus polarization interaction terms are primarily responsible for overall stabilization, while the charge‐transfer term is negligibly small and virtually identical for both adducts. The computed harmonic vibrational frequencies for acetonitrile correlate excellently with the experimental ones (r²>0.9998 for almost all cases, while for the BLYP level, r²=1). It is shown for the first time that the experimentally observed blue shifts of the ν_CN mode are caused even by formation of 1:1 adducts, contrary to the previously accepted opinions. The CCD and QCISD, as well as the BPW91 and BP86 levels of theory predict almost excellently the ν_CN mode blue shift upon adduct formation, while the BLYP and B3LYP levels perform significantly poorer. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Electrochemiluminescence Studies of Phosphorescent Dopant and Host Molecules of Polymer Light-emitting Diodes

Electrochemiluminescence (ECL) from tris(2‐phenylpyridine)irdium [Ir(ppy)₃] was investigated following cross reaction of its anion with oxidized poly(N‐vinyl‐carbazole) (PVK) and its cation with reduced 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD). Both cross reactions show Ir(ppy)₃ emission and the cross reaction of PVK^+·/Ir(ppy)⁻₃ showed the highest ECL intensity. The comparisons of the reaction enthalpy and the energy of Ir(ppy)₃ light emitting shows that reaction between PVK^+· and Ir(ppy)⁻₃ is energy sufficient to populate metal‐to‐ligand charge transfer (MLCT) excited singlet (3.04 eV) of Ir(ppy)₃, while the reaction between Ir(ppy)⁺₃ and PBD^{− ·} is energy efficient to populate MLCT excited triplet (2.4 eV). The ECL result in solution reveals that the energy released from charge transfer between the Ir(ppy)₃ and PVK or PBD is sufficient to produce the excited state of Ir(ppy)₃ in solid polymer light‐emitting diodes (PLEDs) based on PVK:PBD hosts doped by Ir(ppy)₃. These results obtained will provide further insight into charge‐transfer excitation in PLEDs.     

Formation of Dianions in Helium Nanodroplets

The formation of dianions in helium nanodroplets is reported for the first time. The fullerene cluster dianions (C₆₀)_n^2? and (C₇₀)_n^2? were observed by mass spectrometry for n≥5 when helium droplets containing the appropriate fullerene were subjected to electron impact at approximately 22 eV. A new mechanism for dianion formation is described, which involves a two‐electron transfer from the metastable He^? ion. As well as the prospect of studying other dianions at low temperature using helium nanodroplets, this work opens up the possibility of a wider investigation of the chemistry of He^?, a new electron‐donating reagent.     

An approximate description of the double capture process in He2+ + He collisions with static correlation

It is shown that the process of resonant double electron capture in high energy He²⁺+He collisions can be approximately described by a sum over products of one-electron CDW amplitudes. The summation coefficients are determined by stationary ground-state calculations with CI wavefunctions. Total and differential cross sections are calculated and compared with experimental values.