Solvated positron chemistry. II. The reaction of hydrated positrons with Cl−, Br− and I− ions

The reaction of the hydrated positron, e_aq⁺ with Cl^?, Br^?, and I^? ions in aqueous solutions was studied by means of positron The measured angular correlation curves for [Cl^?, e⁺], [Br^?, e⁺, and [I^?, e⁺] bound states were in good agreement with th Because of this agreement and the fact that the calculated positron wavefunctions penetrate far outside the X^? ions in the [X^?, e⁺] sta propose that a bubble is formed around the [X^?, e⁺] state, similar to the Ps bubble found in nearly all liquids. F^?ions did not react w Preliminary results showed that CN^? ions react with e_aq⁺ while OH^?ions are non reactive. The rate constants were 3.9 × 10¹⁰ M^?1 s^?1, 4.4 × 10¹⁰ M^?1 s^?1, and 6.3 × 10¹⁰ M^?1 s^?1 for Cl^?, Br^?, and I^?, respectively, at low (? 0.03 M) X^? concentrations. A 25% decrease in the rate constant caused by the addition of 1 M ethanol to the I^? solutions was i The influence of halide ions on the positronium (Ps) yields in pure water was studied by use of lifetime measurements. The Cl^?, Br^?, and I^? ions reduced the Ps yields at low concentrations (? 0.03 M), while F^? ions only reduced the Ps-yield However, the Ps yields saturated (e.g. at ≈ 21% ortho-Ps yield in the Cl^? case) at higher concentrations. This saturation and the high-concentration effects-in the angular correlation results were interpreted as caused by rather complicated spur effects, wh It is proposed that spur electrons may pick off the positron from the [X^?, e⁺ states with an efficiency which depends on the structure of the     

b 1Σ+ emissions from group V-VII diatomic molecules: bo+ → X10+, X21 emissions of SbBr

Chemiluminescence studies of the reactions of microwave-discharged oxygen with SbBr₃ have led to the observation of some band sequences in the near infrared region which are attributed to b0⁺ → X₁0⁺ and b0⁺ → X₂1 transitions of SbBr. Analysis of the spectra yielded T_e values for the X₂1 and b0⁺ states of 874 ± 10 and 12756 ± 10 cm^?1, respectively, and vibrational frequencies in the X₁0⁺, X₂1 and b0⁺ states of ω′'_e(X₁, X₂) = 257 ± 10 and ω′_e(b) = 270 ± 10cm^?1.     

Electrochemical oxidation of HCOONa on Pt in acidic solutions

The electrooxidation of HCOONa was carried out over a wide range of pH on Pt. HCOO⁻ and its associated form of HCOOH do not show any difference in electrochemical behaviour. A voltammetric study demonstrates the formation of two kinds of poisoning species in the hydrogen (X₁) and double-layer (X₂) regions. Their dependences on the potential and pH were examined. Constant polarization measurements give the rate expression, i = k(α_H⁺)^−0.43 exp(0.4Fφ_n/RT), independent of the concentrations of HCOO⁻ and HCOOH. The rate-determining step is concluded to be HCOO⁻ (a) → COO⁻ (a)+H⁺ + e⁻ or HCOOH(a) → COOH(a)+H⁺ + e⁻. The negative reaction order with respect to H⁺ was explained through the retarding action of X₂. The nature of X₁ and X₂ is discussed.     

Resonance-enhanced multiphoton ionization of molecular hydrogen via the E,F1Σg+ state: Photoelectron energy and angular distributions

Photoelectron energy and angular distributions are measured for the 2+1 multiphoton ionization process H₂ X¹Σ_g⁺ (ν = 0,J) + 2hv → E,F¹Σ_g⁺(ν_E,J_E = J) + hν → H₂⁺X²Σ_g⁺ (ν⁺) + e^?, for ν_E = 0, 1, or 2 and for J_E = 0 or 1 of the inner well of the double-minimum E,F state. Although a strong preference is found for ν⁺ = ν_E, the detailed H₂⁺ vibrational distribution does not exhibit Franck-Condon behavior, and the photoelectron angular distributions vary markedly with both the J_E value of the intermediate state and the ν⁺ value of the ion.     

Theoretical study of spectroscopic parameters of alkali -Al and alkaline earth-Al dimers

The ground states of alkali-Al dimers (AlLi, AlNa, AlK, AlRb and AlCs) and alkaline earth-Al dimers (AlBe, AlMg, AlCa, AlSr and AlBa) along with their monovalent anions and cations were assigned based on the results of calculations. Bond lengths r _e , harmonic vibrational frequencies ω _e and dissociation energies D ₀ of these species were obtained. For neutral dimers, we also calculated adiabatic electron affinities (EA) and adiabatic ionization energies (IE). The present results are in agreement with the available experimental and other theoretical data. The ground state symmetry of AlLi, AlNa, AlK, AlRb and AlCs is ¹ Σ⁺. The ground state symmetry of AlBe⁺, AlMg⁺, AlCa⁺, AlSr⁺ and AlBa⁺ is also ¹Σ⁺. The ground state of AlLi^?, AlNa^?, AlK^?, AlRb^? and AlCs^? is ² Π, and is the same as in the isoelectronic neutral Al-alkaline-earth dimers. For both the alkali-Al and alkaline earth-Al neutral AlX species, the bond length increases monotonously with increasing atomic number of X. For the alkali-Al ions, energies of dissociation via the channels AlX^? → Al + X^? and AlX⁺ → Al + X⁺ are smaller than the energies of dissociation via the channel AlX^? → X + Al^? andAlX⁺ → X + Al⁺, respectively. While the opposite dissociation manner is found for alkaline earth-Al anions.     

b1Σ+ Emissions from group V–VII diatomic molecules. b 0+ → X1 0+, X2 1 emissions of AsI and SbI

Chemiluminescence from the b 0⁺ → X₁ 0⁺ band system of AsI and of the b 0⁺ → X₁ 0⁺, X₂ 1 systems of SbI in the near-infrared spectral region has been observed in a discharge flow system. Analysis of the spectra led to the spectroscopic constants (in cm^?1) of AsI: ω_e(X₁, X₂) = 257 ± 2, ω_ex_e(X₁, X₂) = 0.82 ± 0.2, T_e(b 0⁺) = 11738 ± 5, ω_e(b 0⁺) = 271 ± 2, ω_ex_e(b 0⁺) = 0.66 ± 0.2, and of SbI: T_e(X₂ 1) = 965 ± 10, ω_e(X₁, X₂) = 206 ± 6, T_e(b 0⁺) = 12328 ± 10, ω_e(b 0⁺) = 211 ± 6. The intensity ratio of the two sub-systems b 0⁺ → X₂ 1 and b 0⁺→ X₁ 0⁺ was found to be ≈0.013 in the case of SbI and ? 0.01 for AsI.     

b 1Σ+ and a 1Δ emissions from group VI—VI diatomic molecules: b0+ → X10+, X21 emissions of TeSe

Near-infrared emissions of the b0⁺ → X₁0⁺, X₂1 band systems of TeSe have been observed in a discharge flow system. Analysis of the spectra yielded T_e values of the X₂1 and b0⁺ states of 1235 ± 5 cm^?1 and 8794 ± 5 cm^?1, respectively, and a vibrational spacing in the b0⁺ state of ω_e(b) = 294 ± 3 cm^?1.     

Chemi-ionization reactions of photo-excited K atoms

Ion production resulting from excitation of K atoms to m²P (m ? 6) levels has been observed in mixtures of K with various species. Mass spectrometric data provide direct evidence for the occurrence of K(m²P) + K(4 ²S) → K₂⁺ + e^? and are consistent with the formation of unstable KX⁺ ions from K(m²P) + X → KX⁺ + e^? for X = C₂H₄, CH₄, N₂.     

On the mechanism of conductivity of ammonium salts

The conductivities of HSO₄^?-doped (NH₄)₂SO₄ (AS) and NH₄H₂PO₄ (ADP) crystals are investigated in the temperature range 25°?180°C. The mobility of the charge carriers (protons) is thermally activated and is expressed in accordance with the relation μ = 0.16 exp(?0.49) eV/kT and μ = 0.80 exp(?0.54 eV/kT)cm² V^?1 sec^?1 for AS and ADP crystals, respectively. Three-stage mechanism of proton transport in the lattice of ammonium salt is suggested: (1) formation of the charge carrier NH₄⁺ + X^? → NH₃ + HX, (2) reorientation of the protonated anion HX → XH, and (3) proton jump to the neighbor anion XH + X^? → X^? + HX. The activation energy for mobility is close to that for dielectric relaxation process, i.e., the only thermally activated stage in the mobility process is reorientation of the protonated anion. This very stage is also the rate-determining in the mobility as it is seen from the comparison of the correlation time for proton diffusion and the dielectric relaxation time. These experimental results are in good agreement with the known proton dynamic data in KDP-type ferroelectric crystals.     

b 1Σ+ Emissions from group V–VII diatomic molecules: bO+ → X1 O+ emission of Pl

Chemilluminescence of the bO⁺ → X₁O⁺ band system of P1 has been observed in a discharge flow system. Thirty-eight bands of the sequences, δν = +2, +1, 0, ?1, ?2 and ?3 were recorded photoelectrically at medium resolution. Evidence is presented that the vibrational numering assigned to the bands in the recently published first analysis of this system has to be modified. The re-analysis leads to the new constants (in cm ^?1) T_e = 11135 ± 5, ω′_e 400 ± 2, ω_e′_e = 1.4 ± 0.3, ω″_e = 372 ±2 and ωχ″_e, 1.4 ± 0.3 for the bO⁺ and χ₁ states, respectively. An upper limit of 0.01 was found for the ratio of the (0.0) band intensifies of the two sub-systems bO⁺ → χ₂ 1 and bO⁺ → χ₁O⁺.     

Rate coefficients at 297 K for proton transfer reactions with H2O. Comparisons with classical theories and exothermicity

Rate coefficients for proton transfer reactions of the type XH⁺ + H₂O → H₃O⁺ + X where X = H₂, CH₄, CO, N₂, CO₂ and N₂O and the type H₂O + X^? → XH + OH^? where X = H, NH₂ and C₂H₅NH have been measured at 297 K using the flowing afterglow technique. The results compare favourably with the predictions of the average-dipole-orientation theory. A trend is observed with exothermicity on a plot of (k_exp/k_ADO)_{298 K} versus ?ΔH_{298 K}⁰. The question is raised whether the relatively low probability observed for slightly exothermic proton transfer reactions is a consequence of reaction mechanism or results from the presence of a small activation energy barrier.     

Fluorescence spectrum of the benzene radical cation in solid argon

Argon/benzene samples were condensed at 12 K with continuous argon resonance radiation. Laser excitation at 421 nm produced a weak emission with structure at 19770, 19140 and 18290 cm^?1, assigned to the ²A_2u → ²E_1g emission of C₆H₆⁺. Observation of 630 and 1480 cm^?1 intervals for the vibrations v₁₈ (e_2g) and v₆ (e_2g), respectively, supports this assignment.     

Luminescence in near-thermal charge exchange. III. CH(+) and CD(+) A → X emission from He+ C2H2 and He+ + C2D2

A pulsed ICR cell fitted with synchronous photon counting equipment is used to investigate the emission produced between 185 and 500 nm by near-thermal charge exchange between He⁺ and C₂H₂ (C₂D₂). The emission bands observed are A ²Δ → X²π and (weakly) B²Σ^? → X²π in CH(CD) and A ¹π → X¹Σ in CH⁺(CD⁺). Wavelength measurements on the bandheads of the (0,0) and (0,1) bands of CD⁺ A → X are used to evaluate vibrational constants of CH⁺(CD⁺) X¹Σ⁺. The results are (in cm^?1): ω_e = 2869 ± 27 (2106 ± 20); ω_eχ_e = 65 ± 13 (35 ± 7). These constants are used to calculate Morse-potential Franck—Condon factors and vibrational branching ratios for CH⁺ and CD⁺ A → X emission. The spectral distributions and the (relatively low) absolute emission rates produced by He⁺/C₂H₂(C₂D₂) charge exchange are briefly discussed in the light of presently available information on the charge transfer reaction and on the excited states of C₂H_2?⁺     

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part VI. Dimethylglyoxime electroreduction from weakly acidic aqueous solutions in the presence of I− and SCN−

An investigation of the _d-effect in the absence of ionic specific adsorption shows that the overall charge of the reactants in dimethylglyoxime (DMG) electroreduction on mercury from aqueous solutions of pH?2 equals+1, in agreement with a protonation reaction either preceding (DMG + H⁺DMGH^++e → products) or else simultaneous with (DMG + H⁺ + e → products) the charge transfer. In the presence of the specifically adsorbed supporting anions I^? and SCN^? the logarithm Φ of the rate constant for DMG electroreduction corrected for diffuse-layer effects decreases linearly with an increase in the absolute value |q_i| of the charge density at the inner Helmholtz plane due to the adsorbed anions. This behaviour is explained semiquantitatively by assuming that protonation takes place simultaneously with charge transfer, with the DMG molecule in the adsorbed state and the H₃O⁺ ion in the non-adsorbed state. In this way the H₃O⁺ ion, due to the screening effect of the surrounding diffuse-layer ions, escapes the accelerating attractive effect exerted by the adsorbed I^? or SCN^? ions; on the other hand these latter anions exert a retarding repulsive effect upon the electron transfer from the metal to the adsorbed DMG molecule.     

Theoretical condiserations regarding the existence of PsO and PsS+

At has been proposed from experimental studies and in analogy with hydrogen compounds that PsO may be an entity of some importance, or an intermediate, in the reaction of positronium, Ps, with aqueous oxyacid species such as H₂PO^?₄, HSO^?₄, ClO^?₄, and NO^?₃. This communication explores the stability of PsO and PsS, or [0^?: e⁺] and [S^?:e⁺], respectively, relative to dissociation into Ps and O(³P) or S(³P) on the basis of restricted Hartree-Fock calculations for the PsO and PsS systems and certain correlation correction arguments. We obtain a reasonable lower estimate of the dissociation energy to Y + Ps of ? ?0.47 eV for PsO and ? ?0.70 eV for PsS. It is suggested that a modest correlation correction to the positron affinity (PA) of O^? would very probably lead to a bound state system for PsO.     

Experimental and theoretical studies of the valence-shell dipole excitation spectrum and absolute photoabsorption cross section of hydrogen fluoride

Absolute cross sectional measurements are reported of the valence-shell dipole excitation spectrum of HF obtained from suitably calibrated high impact energy, small momentum transfer, electron energy-loss scattering intensities. Detailed assignments are provided of all prominent features observed on the basis of concomitant single- and coupled-channel RPAE calculations. The measured spectrum, obtained at an energy resolution of = 0.06 eV (fwhm) in the = 9 to 21 eV interval, includes a dissociative feature centered at = 10.35 eV assigned as X¹Σ⁺ → (1π^?14σ)A¹Π, as well as numerous strong, sharp bands in the = 13 to 16 eV excitation energy region. These bands are attributed on basis of the present calculations to Rydberg (1π^?1npπ)-valence (3σ^?14σ) mixing in X¹Σ⁺ → ¹Σ⁺ excitation symmetry, which gives rise to a long conventional progression, and to strong 1π → nsσ, moderate 1π → ndσ, and weak 1π → npσ Rydberg series in X¹Σ⁺ → ¹Π excitation symmetry. A weaker 1π → ndπ Rydberg series also contributes to the spectrum in X¹Σ⁺ → ¹Σ⁺ symmetry. The calculated and measured excitation energies and f numbers, particularly for the X¹Σ → (1π^?14σ)A¹Π, → (1π^?13pπ)B¹Σ⁺, → (1π^?13sσ)C¹Π, and → (3σ^?14σ)D¹Σ⁺ transitions, are in good quantitative accord, suggesting that the overall nature of the HF spectrum is generally clarified on basis of the present studies. Finally, tentative assignments are provided of weak features observed above the 1π^?1 ionization threshold. As in previously reported joint experimental and theoretical studies of the valence-shell spectrum of F₂, high-resolution optical VUV measurements and calculated potential energy curves aid in the assignment and clarification of the HF spectrum.     

Ionogenic equilibria of (φ3CCl + HgCl2) and ((pClC6H4)3CCl + HgCl2) in CH2Cl2

Binary ionogenic equilibria (RX + MtX_x ? R⁺MtX_{n + l}^? ? R⁺ + MtX_{n + 1}^?, R = φ₃C, (pClC₆H₄)₃C; X = Cl; Mt = Hg) are studied in CH₂Cl₂ by conductivity and u.v. spectroscopy. The importance of such studies to cationic polymerisation is emphasised. The equilibrium constants, the thermodynamic parameters and the molar conductivities of the individual ions are given and the results discussed both in terms of a comparison between the two systems studied and in terms of a comparison with similar data in the literature.     

Theoretical study on a chemosensor for fluoride anion‐based on a urea derivative

The sensing mechanism of the N‐Phenyl‐N′‐(3‐quinolinyl)urea (PQU) chemosensor for fluoride anion has been investigated by density functional theory/time‐dependent density function theory. The double intermolecular hydrogen bonds are formed between the three anions (X^??F^?, AcO^?, Cl^?) and the urea fragment of PQU. In the S₀ states, the H_b? X^? hydrogen bonds are slightly stronger than the H_a? X^? hydrogen bonds and the fluoride‐induced deprotonation occurs at the N? H_b position rather than at the N? H_a position. Consequently, the absorption peaks, including an intramolecular charge transfer transition and a ππ* transition, are significantly red‐shifted. Thermodynamic calculations confirm that the deprotonation in the ground state is favorable in energy only when excess fluoride anion exists. Along with the S₀ → S₁ transition, the H_a? X^? hydrogen bonds strengthen and the H_b? X^? hydrogen bonds weaken. However, the emission spectra of [PQU‐H_b]^?, instead of [PQU‐H_a]^?, are observed upon addition of fluoride anion. © 2013 Wiley Periodicals, Inc.     

Gas phase oxidative-addition reactions of alkyl radicals at complexed cobalt(II) centres

Negative chemical ionisation mass spectrometry is used as a probe to identify reactions between hydrocarbon radicals and cornplexed cobalt(II) centres in the gas phase. Methane NCI mass spectra of a series of cobalt(II) complexes containing O₄, O₂N₂ and N₄ donor atom sets are characterised by adduct ions of the form [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Formation of such ionic species has been rationalised in terms of a one-electron oxidative-addition mechanism involving attack by hydrocarbon plasma-derived alkyl radicals at the metal centre prior to electron capture: Co^IIL_n + R^? → RCo^IIIL_n$\text{e}{}^{\mathrm{?}}$ [Co^IL_n]^?. The competing resonance electron attachment reaction: Co^IIL_n$\text{e}{}^{\mathrm{?}}$ also occurs within the ion source.