Difference In Ionization Potential Research Articles

Optically detected electron spin resonance studies of electrons and holes involved in geminate recombination in non-polar solutions

Optically detected electron spin resonance spectra have been used to identify geminate electrons and free holes in non-polar hydrocarbons. The temperature dependence of the spectra has been investigated in terms of excess electrons and also electrons solvated in clusters by water molecules. The line intensity of an excess electron increases with falling temperature, while the linewidth decreases with rising temperature. The signal from a hydrated electron is observed at higher temperatures in comparison with that from an uncaptured electron. Its intensity increases with the concentration of water in the solvent. The collapsed spectrum width has been employed to estimate the charge-transfer rate constants in the recombination of free holes in p-xylene and in benzene. The signals from holes are effectively suppressed by adding compounds with low ionization potentials. The suppression efficiency increases with the difference in ionization potentials between the solvent and admixture.

Rydberg transitions in the bichromophoric molecules tetramethyl-1,3-cyclobutanedithione (TMCBDT) and tetramethyl-3-thiocyclobutan-1-one (TMTCB)

The vacuum ultraviolet spectra of tetramethyl-1,3-cyclobutanedithione (TMCBDT) and tetramethyl-3-thio-cyclobutan-1-one (TMTCB) in the 140–240 nm range are reported. Each spectrum is analysed and shown to consist of various Rydberg series. While transitions from the non-bonding orbital on the C=S to ns S, np S and nd S Rydberg orbitals dominate the spectra of both compounds, a short series assigned to the non-bonding C=O to ns O orbitals is observed in TMTCB. The splitting of the n orbitals in TMCBDT is considerably smaller than that in TMTCB or TMCBD. The difference in the n orbital splitting in the two symmetrical molecules, TMCBD and TMCBDT, is attributed to the difference between the orbital energy spacings (n CO or n CS) and the closest-lying σ relay orbital responsible for the through-bond interaction. The large splitting in TMTCB is due to the difference in ionization potential between sulphur and oxygen. For this same reason the two highest occupied orbitals in TMCBDT fit into the conventional conc...

Analysis of polyaromatic hydrocarbon mixtures with laser ionization gas chromatography/mass spectrometry

Excimer laser induced multiphoton ionization has been utilized for ion generation in capillary gas chromatography/mass spectrometry and the technique applied to the separation and detection of polyaromatic hydrocarbons. Detection limits as low as 200 fg and linearity over a range of 5 x 10/sup +4/ were obtained for the polyaromatic hydrocarbons examined. Multiphoton ionization mass spectra were dominated by parent ions. Selective ionization based upon small differences in ionization potentials has been demonstrated for coeluting chrysene and triphenylene. Instrumental parameters have been investigated to assess improvements in sensitivity.

Quantification of aromatic components in mineral oils

Fluorobenzene CIMS preferentially ionizes aromatic components in hydrocarbon mixtures. The relative reactivity of C 6H 5F + depends upon the difference in ionization potential between the aromatic compound and fluorobenzene.

Electron Capture Into Excited States in Collisions Between Multiply Charged Ions and Atoms

We discuss some recent experimental results on charge transfer into excited states in collisions between multiply charged ions and Li atoms. Beams of He2+, Cq+, Oq+ (q = 1, 2, 3) ions in the energy range of (10-200)q keV were crossed with a thermal Li beam produced by an oven. From measurements of the radiation emitted by the decay of the excited ion states we were able to determine absolute cross sections for electron capture into specific n, l-states. The wavelength range covered is about 10-700 nm. For Cq+ and Oq+, we also used a molecular hydrogen target. Comparing the results for both targets, we can explain the differences as a result of the difference in ionization potential. The importance of metastable fractions in the Cq+, Oq+ ion beams is discussed.

Oxidation of the surface ofA15Nb3Ge

An oxide layer grown on the $A15$ ${\mathrm{Nb}}_{3}$Ge surface after exposure to pure oxygen is found to be mainly ${\mathrm{Nb}}_{2}$${\mathrm{O}}_{5}$ from the in situ observation of x-ray photoelectron spectroscopy. The thickness of the ${\mathrm{Nb}}_{2}$${\mathrm{O}}_{5}$ layer varies with the oxidation time by following the logarithmic-growth law. The oxide layer serves as a protective stable film with a thickness of around 1.5 nm. Beneath the oxide layer an Nb-deficient layer occurs in a thickness of 2 nm due to the preferential diffusion of Nb atoms. This is caused by the contact potential difference between the ${\mathrm{Nb}}_{3}$Ge and adsorbed oxygen layers and the ionization potential difference between Nb and Ge atoms.

Charge Transfer from the Solvent Radical Cation to Solutes Studied in Pulse‐Irradiated Liquid n‐Butyl Chloride

AbstractCharge transfer from n‐butyl chloride radical cations (BuCl+) to 11 solutes (S) (alkanes, alkenes, aromatics, and amines) was studied by pulse radiolysis. Using a mechanism proposed for radiation‐induced ionic processes in liquid n‐butyl chloride the rate constants of the reactionmagnified imagewere determined. At gas phase ionization potential differences ΔI = (IBuCl‐Is) smaller than 1.5 eV the rate constants increased rapidly with increasing ΔI and reached for larger ΔI nearly constant values of about 1010 dm3 mol−1 s−1. The dependence of the rate constants on the ionization potential differences k vs. ΔI is explained in terms of a two‐step process consisting of migration of solvent cations and electron transfer from the solute molecule to the solvent cation. The probability of the last step was calculated using the Franck‐Condon principle. In the framework of a simplified model taking into account vibrational stretching and deformation modes of the reactants and solvent modes in thermally averaged form a reasonable fit of the k vs. ΔI behaviour was obtained.

Transfer of the positive charge in non-polar liquids studied by pulse radiolysis

After electron pulse irradiation of various liquid alkanes broad optical absorption bands between 400 and 1000 nm were measured. From the time behaviour of the absorption and its dependence on scavengers and added solutes it is concluded that alkane radical cations were observed. The solute cation formation kinetics studied and the competition of n-heptane radical cations and solutes added for a common precurser provides evidence that also in n-heptane at times ≤10 −9s a fast migrating radical cation state (hole) can exist. The solute concentrations reducing the n-heptane radical cation absorption by 50% (C 50 values) show a pronounced dependence on the ionization potential difference between solvent and solute. A similar dependence was observed also for the rate constants of the charge transfer reaction CCl 4 + + S → S + + CCl 4 and is explained by the influence of the Franck-Condon factor.

Spontaneous electromagnetic radiation caused by binary ion-atom collisions in the quasiresonant case

The process of spontaneous electromagnetic radiation in the reaction A/sup +/ + B ..-->.. A + B/sup +/ + h..omega.. is studied. Here A and B are the same kind of atoms or atoms with small differences in ionization potentials (quasiresonant case). Differential cross section, energy spectrum of the emitted photons, and total intensity of electromagnetic radiation are determined for thermal velocities of relative motion. Results are applicable in a wide range of temperatures: 500< or = T< or = 50,000 K. It is shown that the radiation spectrum is very broad and the radiation intensity is considerable.

Ground-state charge transfer and electronegativity equalization

The intuitive picture suggesting that ground-state charge transfer is associated with differences in ionization potentials of donor and acceptor molecules is studied in terms of an MC-SCF scheme. This leads to the definition of effective molecular electronegativities and to the formulation of a principle of electronegativity equalization as the condition for charge transfer in the ground state at distances where binding effects proper are negligible. Even in that extreme case charge transfer is found to be directional, because of its dependence on electronegativity differences and on an effective intermolecular Coulomb integral. The example of a few Ag atoms in the presence of a Si sp3 orbital is given as a simple illustration.

Photochemistry of aliphatic aldehydes

The photochemistry of alkanals in dilute solutions and in the presence of olefins and hydrogen donors was analysed and the results obtained are discussed taking as reference the photochemical behaviour of the alkanones. Intermolecular and intramolecular hydrogen abstraction take place in alkanals and alkanones with similar rates. However, there are differences in their behaviour towards unsaturated compounds that can be related to differences in ionization potentials and electron affinities. A distinct feature of alkanal photochemistry is the relevance of auto-quenching in both the singlet and triplet states. The singlet lifetimes of the alkanals, when extrapolated to zero alkanal concentration, decrease with α substitution. The results obtained indicate that this effect is not due to type I photofragmentation.

Charge Transfer from the Carbon Tetrachloride Radical Cation to Alkyl Chlorides, Alkanes, Alkenes and Aromatics

AbstractCharge transfer from carbon tetrachloride radical cations to 17 solutes (alkyl chlorides, n‐ and c‐alkanes, alkenes and aromatics) was studied by pulse radiolysis. ‐ At gas‐phase ionization potential differences ΔI = (ICCl4 ‐ Is) smaller than 0.8 eV rate constants of the reactionmagnified imageup to two orders of magnitude lower than expected for a diffusion controlled reaction have been determined. The dependence of the rate constants on the ionization potential differences k vs. ΔI is explained in terms of a two‐step process consisting of migration of solvent cations and electron transfer from the scavenger molecule to the solvent cation. The probability of the last step was calculated using the Franck‐Condon principle. In the framework of a simplified model taking into account vibrational stretching and deformation modes reasonable fits of the k vs. ΔI behaviour were obtained.

Theory of electron transfer in donor–acceptor pairs

AbstractThe wave functions of donor–acceptor pairs before and after electron transfer are written as a product of the electron‐vibrational wave functions of the donor and acceptor with allowance for the change in the number of electrons on these particles by one after transition. In this approximation, the energy of the initial state is represented as a sum of the electron‐vibrational levels of the donor and acceptor and that of the final state as a sum of donor cation and acceptor anion levels. Formulas for the electron transfer probability of symmetrical and nonsymmetrical donor–acceptor pairs have been derived that express the dependence of this process on the ionization potential difference of the donor and the electron affinity of the acceptor, on the vibrational frequencies of these particles, and on temperature.

Experimental investigation of the critical ionization velocity in gas mixtures

The critical ionization velocity which is of cosmogonic and astrophysical interest has hitherto mainly been investigated for pure gases. Since in space we always have gas mixtures, it is of interest also to study gas mixtures. The present report, which is a summary of a more detailed report (Axnas, 1976), summarizes the results of systematic experiments on the critical ionization velocity as a function of the mixing ratio for binary gas mixtures of H2, He, N2, O2, Ne and Ar. The apparatus used is a coaxial plasma gun with an azimuthal magnetic field. The discharge parameters are chosen so that the plasma is weakly ionized. In some of the mixtures it is found that one of the components tends to dominate in the sense that only a small amount (regarding volume) of that component is needed for the discharge to adopt a limiting velocity close to that for the pure component. Thus in a mixture between a heavy and a light component having nearly equal ionization potentials, the heavy component dominates. Also, if there is a considerable difference in ionization potential between the components, the component with the lowest ionization potential tends to dominate.

The Silver Halides: A Localized Molecular Orbital Treatment-III*

This paper illustrates a possible approach to the empirical description of bonding in the silver halide solid states. ~n LCAO-MO treatr:tentof the localized bonding unit corresponding to the first co-ordination sphere about each silver atom is employed. Approximations and assumptIOns required by this treatment are discussed. The model is parameterized to be consistent ;Nlth bond energies, from Born-Haber cycle data, absorption band edges and electronegativities, as ionization potential differences, for the structures considered. The results of the calculations are compared to lattice parameters photoelectron spectroscoPic energy levels and known surface characteristics.

Ion-ion collisions and element separation effects in the boundary region of a plasma surrounded by neutral gas

In the boundary region between a plasma and neutral gas, the temperature is low (some thousand degrees). Then the Coulomb cross-section is large compared with other collision cross-sections. The influence of ion-ion collisions in the boundary region is discussed. In particular a simple formula is derived for the separation between different kinds of constituents. This separation depends on different collision cross-sections for diffusion and seems to be especially large when resonant charge exchange collisions are involved. These diffusive processes of importance in impermeable plasmas are also compared with separation processes due to a difference in ionization potential, which is known to occur in permeable plasmas. Different isotopes have the same ionization potential and the same charge exchange cross-sections. The separation processes described above are, therefore, likely to give element, but not isotope, separation.

A model for the hydrogen bond

A MODEL OF THE LINEAR HYDROGEN BOND HAS BEEN DEVISED WHICH IS CHARACTERIZED BY THREE PHYSICAL PARAMETERS OF THE ISOLATED ELECTRON DONOR AND PROTON DONOR MOLECULES: mu(A-H), the bond dipole moment; DeltaI, the difference in ionization potential between that of the electron donor and the corresponding noble gas atom; and l, the length of the electron donor lone-pair of electrons. The model is able to explain dimerization energy, charge transfer, internuclear separation, directionality, stretching force constants, dimer dipole moment, and infrared intensity enhancement.

ICR mass spectra of fluoroalkenes: III. Thermal ion-molecule reactions in C 2HF 3 and C 2F 4 by ion cyclotron resonance

The ion—molecule reactions of both parent and fragment ions in C 2HF 3 and C 2F 4 have been observed. Absolute rate constants have been measured for the parent ion reactions in both systems and in the mixed system. In each case, the only condensation reaction involves elimination of the ·CF 3 radical although other reaction channels are thermodynamically allowed. The rates of the CF 3 elimination reactions vary from 0.3 to 5.6 X 10 −11 cm 3 molecule −1 sec −1. Substantial decreases in the rates are observed at low pressures. This effect is attributed to internal energy in the reactant ions. The reversible charge transfer reaction was also observed in the mixed system. The equilibrium constant for this reaction has been measured yielding Δ G D = 0.023 ± 0.001 eV as the free energy of the charge exchange (C 2F 4 ⨥ → C 2HF 3 ⨥). This value agrees well with previously determined differences in ionization potentials. Thermodynamic implications are discussed for the fragment ion reactions.

Photoelectron microscopy: a new approach to mapping organic and biological surfaces.

A general method of imaging organic and biological surfaces based on the photoelectric effect is reported. For the experiments, a photoelectron emission microscope was constructed. It is an ultrahigh vacuum instrument using electrostatic electron lenses, microchannel plate image intensifier, cold stage, hydrogen excitation source, and magnesium fluoride optics. The organic surfaces examined were grid patterns of acridine orange, fluorescein, and benzo(a)pyrene on a Butvar surface. A biological sample, sectioned rat epididymis, was also imaged by the new photoelectron microscope. Good contrast was obtained in these initial low magnification experiments. These data demonstrate the feasibility of mapping biological surfaces according to differences in ionization potentials of exposed molecules. A number of technical difficulties, such as the intensity of the excitation source, must be solved before high resolution experiments are practical. However, it is probable that this approach can be useful, even at low magnifications, in determination of the properties of organic and biological surfaces.

First Ionization Potentials of Th, Np, and Pu by Surface Ionization

The surface ionization comparison technique was used to measure the first ionization potentials of Th, Np, and Pu relative to U. The differences in ionization potentials (ΔI.P.) obtained were: ΔI.P.(U–Th) = −1.29 ± 0.26 eV; ΔI.P.(U–Np) = 0.03 ± 0.01; and ΔI.P.(U–Pu) = 0.48 ± 0.02. The I.P. of U had previously been determined in this laboratory to be 6.19 ± 0.06 eV. Based on this value, the I.P. of Th is 7.5 ± 0.3 eV; Np, 6.16 ± 0.06; and Pu, 5.71 ± 0.06.