Small-angle electron scattering by formaldehyde and ketene: Effects of electron correlation and chemical binding

The total (elastic plus inelastic) intensities of 51 keV electrons scattered by H₂CO and H₂CCO have been measured over a range of K = (4π/λ) sin(θ/2) = 1–9.5 Å^?1 and compared with the theoretical intensities calculated with SCF and CI wave functions. Significant discrepancies are found between the experimental intensities and the theoretical ones based on the SCF wave functions. Most of the chemical binding and electron correlation effects observed in the total scattered intensities are reproduced by the theoretical intensities based on the CI wave functions calculated with the basis set including polarization functions on all atoms. © 1992 John Wiley & Sons, Inc.     

Experimental and theoretical studies of small-angle electron scattering by the water molecule

The total (elastic plus inelastic) intensities of 51 keV electrons scattered by water molecules have been measured over a range of 1 ≦ K = (4π/λ) sin(θ/2) ≦ 12 Å^?1. A computer program, ELIC, has been written for calculating the total intensities of electrons scattered by free molecules. The intensities can be calculated with self-consistent field and configuration interaction wavefunctions. The theoretical intensities based on a CI wavefunction are in good agreement with the observed intensities.     

X-ray scattering by water molecules studied by using synchrotron radiation

The energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle-dispersive-type diffractometer and synchrotron radiation as an X-ray source. A silicon (111) monochrometer was used to obtain incident X-rays with the wavelengths of (1.543/n) Å (n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [s = (4π/λ) sin Å] larger than 8 Å^?1. The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74–5.0 Å^?1. Experimental difference intensities Δσ_ee and Δσ_ne were obtained separately by combining the X-ray and high-energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double-zeta plus polarization functions. © 1994 John Wiley & Sons, Inc.     

Molecular ordering in some liquid aromatic hydrocarbons

This study presents a comparison of the structures and molecular correlations for the linear aromatic hydrocarbons: benzene, naphthalene, and anthracene in the liquid phase, performed for the first time by the method of X-ray diffraction. Also for the first time the X-ray diffraction results obtained for anthracene at 513?K have been reported. Monochromatic radiation CuK_α was used to determine the scattered radiation intensity between S _min?=?4π?sin?Θ_min/λ?=?0.417?Å^?1 and S _max?=?4π?sin?Θ_max/λ?=?7.06?Å^?1. The mean angular distributions of X-ray scattered intensity were measured and the differential radial distribution functions of electron density (DRDFs) were calculated. The mean distances between the neighbouring molecules and the mean coordination numbers were found. The most probable models of local ordering of these molecules were suggested. Correlations have been found between the number of benzene rings in the molecules studied and their physical properties.     

X-Ray Diffraction Study of Some Liquid Naphthalene Derivatives

Abstract

The structure of the liquids 1-Methylnaphthalene C₁₀H₇—CH₃ and 1-Chloronaphthalene C₁₀H₇—Cl was investigated using X-ray diffraction at 293 K. Monochromatic radiation MoK_α (λ = 0.7107Å) enabled determination of the scattered radiation inteasity between S₀ = 4\pi sin υ₀/λ = 0.430 Å^?1 and S _max = 14.311 Å-1. Angular distributions of X-ray scattered intensity were measured, and differential radial distribution functions of electron density (DRDFs) were calculated. The mean distances between the neighbouring molecules and the ranges of the spheres of intermolecular ordering were found. X-ray structural analysis was applied for determination of the packing coefficient of molecules of the liquids studied. A simple model of short-range arrangement of the molecules was proposed, which seems to be valid for other weakly polar monosubstituted naphthalene derivatives in the liquid phase.     

Kinetics of the reaction of OH radicals with acetylene in 25–8000 torr of air at 296 K

Relative rate techniques were used to study the kinetics of the reaction of OH radicals with acetylene at 296 K in 25–8000 Torr of air, N₂/O₂, or O₂ diluent. Results obtained at total pressures of 25–750 Torr were in good agreement with the literature data. At pressures >3000 Torr, our results were substantially (～35%) lower than that reported previously. The kinetic data obtained over the pressure range 25–8000 Torr are well described (within 15%) by the Troe expression using k_o = (2.92 ± 0.55) × 10^?30 cm⁶ molecule^?2 s^?1, k_∞ = (9.69 ± 0.30) × 10^?13 cm³ molecule^?1 s^?1, and F_c = 0.60. At 760 Torr total pressure, this expression gives k = 8.49 × 10^?13 cm molecule^?1 s^?1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 191–197, 2003     

Manifestations of noncovalent interactions in the solid state. Dimeric and polymeric self-assembly in imidazolium salts via face-to-face cation—cation π-stacking

Abstract

X-ray crystallographic investigation of the tertiary structure of simple 1-methylimidazolium (1-Meim) salts reveals that cation—cation face-to-face π—stacking with interplanar separations in the range typically seen for molecule—molecule and molecule—cation interactions are possible. Two salts are reported. 1-Meim-CF₃SO₃, 1, exists as a centrosymmetric dimer with an interplanar separation of only 3.16 Å. The two imidazolium rings are slipped to the extent that the interaction can be regarded as a manifestation of C—H…C—H dipole interactions. 1-Meim-NO₃ exists as a one-dimensional (1-D) polymer with interplanar separations of 3.65 Å. The cations are not as severely slipped as for 1 and the interactions can be regarded as the result of cation—cation and anion—anion complementary electrostatics. Semi-empirical calculations are used to rationalize the π-π stacking in both 1 and 2. Crystal data: 1-Meim-CF₃SO₃, 1, triclinic, P1, a=6.416(3) Å, b=7.617(4) Å, c=9.569(4) Å, α=85.36(4)°, β=86.08(3)°, γ=85.18(4)°, V=463.6(4) Å,³ Z=2, D_c =1.66 g cm^?3, μ=3.7 cm^?1, T=17°C, R=0.054 and R _w=0.076 for 1241 reflections; 1-Meim-NO₃, 2, monoclinic, P2₁/c, a=9.009(7) Å, b=9.988(6) Å, c=7.308(5) Å, β=94.93(6)°, V=655.2(8) Å,³ Z=4, D_c =1.47 g cm^?3, μ=1.2 cm^?1, T=17°C, R=0.060 and R _w=0.068 for 483 reflections.     

Investigation of the Quasi Binary System BaAu–BaPt

Phase equilibria in the system BaAu–BaPt have been investigated by X‐ray powder diffraction. Depending on composition, three structure types occur, the FeB type for BaAu, and NiAs for BaPt, while the CrB type of structure is adopted in between. The homogeneity range for the CrB type of structure was established to extend from BaPt_0.15Au_0.85 to BaPt_0.90Au_0.10. The respective lattice parameters vary linearly, in accordance with Vegard's law. The crystal structure of the new CrB type compounds have been confirmed by X‐ray powder diffraction for the solid solution range, and by single crystal X‐ray diffraction exemplary for the composition BaAu_0.5Pt_0.5 (Cmcm; a = 4.3915(5) Å; b = 11.9149(12) Å; c = 4.7920(5) Å; Z = 4). BaAu was also established by single crystal structure determination (Pnma; a = 8.3220(10) Å; b = 4.9252(10) Å; c = 6.3844(10) Å; Z = 4) to complete the results. According to ESCA measurements BaAu_0.5Pt_0.5 and BaAu can be formulated as [Ba²⁺·0.5e^?]·[Au^?_0.5·Pt^2?_0.5] and [Ba²⁺·e^?]·[Au^?], respectively.     

Photoinduced electron transfer of [ Ru (bpy)_2 (4, 4'-dcbpy)]~(2 ) with electron donors

Emission quenching of [Ru(bpy)2(4, 4'-dcbpy)] (PF6)2 (1) by benzenamine,4-[2-[5-[4-[4-dimethylamino]phenyl]-4,5-di-hydro-1-phenyl-1H-pyrazol-3-yl]-ethenyl]-N,N-dimetyl (2) or 1, 5-diphenyl-3-(2-phenothiazine)-2-pyrazoline (3) was observed. Measurements of the emission decay of 1 before and after addition of 2 or 3 by single photon counting technique con-finned the observations. The emission quenching of 1 by 2 or 3 was submitted to Stern-Volmer equation. It was calculated that the quenching rate constants (kq) are 5.5 × 109(mol/L)-1s-1 for 2 and 4.0 × 109(mol/L)-1s-1 for 3, respectively. These results indicated a character of dynamic quenching process. The singlet-state of 2 or 3 was also quenched by 1. The quenching behaviors did not conform to the Stern- Volmer equation and involved both static and dynamic quenching processes. The apparent quenching rate constant (kapp) was calculated to be 3 × 109 (mol/L)-1 for the interaction of excited 2 with 1, and 1.2 × 109 (mol/L)-1 for that of excited 3 wit     

Polymerization of neat 2‐ethylhexyl acrylate induced by a pulsed electron beam

The bulk polymerization of 2‐ethylhexyl acrylate (2‐EHA), induced by a pulsed electron beam, was investigated with pulse radiolysis, gravimetry, and Fourier transform infrared spectroscopy. The roles of the dose rate, pulse frequency, and added acrylic acid (AA) in the polymerization of 2‐EHA were examined at ambient temperature. In the range of 12.6–71.2 Gy/pulse, the polymerization of 2‐EHA was dose‐rate‐dependent: at the same total dose, a lower dose rate yielded a higher conversion. Also, a lower pulse rate gave a higher conversion at the same total dose. The addition of up to 10 wt % AA showed no increase in the conversion of 2‐EHA at a low conversion (8 kGy), but at a higher conversion (16 kGy), a 20 wt % increase in the conversion of 2‐EHA was observed. The estimated values (1.6 ± 0.3) × 10^?3 (dm³ s)^3/2 mol^?1 s^?1/2 for k_p(G/2k_t)^1/2 and 2.6 ± 0.8 dm³ s J^?1 for 2k_tG (where k_p is the rate constant of propagation, k_t is the rate constant of bimolecular termination, and G is the yield of free radicals) were obtained at relatively low conversions. The reaction rate constant of the addition of 2‐EHA^· free radicals to the monomer was measured by pulse radiolysis and found to be 2.8 × 10² mol^?1 dm³ s^?1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 196–203, 2003     

Kinetic studies on the metal(II) tartarate–peroxomonosulfate reaction

The kinetics of oxidation of tartaric acid (TAR) by peroxomonosulfate (PMS) in the presence of Cu(II) and Ni(II) ions was studied in the pH range 4.05–5.20 and also in alkaline medium (pH ～12.7). The rate was calculated by measuring the [PMS] at various time intervals. The metal ions concentration range used in the kinetic studies was 2.50 × 10^?5 to 1.00 × 10^?4 M [Cu(II)], 2.50 × 10^?4 to 2.00 × 10^?3M [Ni(II)], 0.05 to 0.10 M [TAR], and µ = 0.15 M. The metal(II) tartarates, not TAR/tartarate, are oxidized by PMS. The oxidation of copper(II) tartarate at the acidic pH shows an appreciable induction period, usually 30–60 min, as in classical autocatalysis reaction. The induction period in nickel(II) tartarate is small. Analysis of the [PMS]–time profile shows that the reactions proceed through autocatalysis. In alkaline medium, the Cu(II) tartarate–PMS reaction involves autocatalysis whereas Ni(II) tartarate obeys simple first‐order kinetics with respect to [PMS]. The calculated rate constants for the initial oxidation (k₁) and catalyzed oxidation (k₂) at [TAR] = 0.05 M, pH 4.05, and 31°C are Cu(II) (1.00 × 10^?4 M): k₁ = 4.12 × 10^?6 s^?1, k₂ = 7.76 × 10^?1 M^?1s^?1 and Ni(II) (1.00 × 10^?3 M): k₁ = 5.80 × 10^?5 s^?1, k₂ = 8.11 × 10^?2 M^?1 s^?1. The results suggest that the initial reaction is the oxidative decarboxylation of the tartarate to an aldehyde. The aldehyde intermediate may react with the alpha hydroxyl group of the tartarate to give a hemi acetal, which may be responsible for the autocatalysis. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 620–630, 2011     

Electron scattering differential cross sections for C2H2, C2H4, and C2H6 by gas phase electron diffraction - binding effects

Experimental differential cross sections for 40 keV electrons scattered by C₂H₂, C₂H₄ and C₂H₆ molecules were measured using the gas electron diffraction method in the range of the scattering variable s from s = 1 A^?1 to s = 30 A^?1. The differential cross sections for neon were also measured and compared with calculated differential cross sections to calibrate the diffractograph. Experimental differential cross sections show significant deviations with respect to theoretical differential cross sections calculated from the Debye-Ehrenfest model, mainly in the range of small scattering angles. The observed differences are connected to chemical binding effects. From the experimental data, an estimation of the binding energy was carried out. The deduced values: ?0.58 ± 0.20 au for C₂H₂, ?0.94 ± 0.30 au for C₂H₄ and ?1.23 ± 0.40 au for C₂H₆ are in agreement with those obtained by thermochemical methods.     

DIRECT SYNTHESIS AND CRYSTAL STRUCTURE OF DIIODOETHYLENDIAMINELEAD(II) DIMETHYLSULFOXIDE

Abstract

A direct method of obtaining PbEnI₂.DMSO is reported. The crystal structure of the compound was determined by X-ray techniques. PbEnI₂.DMSO is triclinic, space group P 1, C₄H₁₄I₂N₂PbS, a=10.225(3), b=10.132(3), c=6.900(2) Å; α=90.83(2), β=88.30(2), γ=106.35(4)°; V=685.6(4) ų; z=2, calculated density 2.92 gcm^?3. Neutral PbEnI₂ complexes are associated with DMSO molecules via H-bonds. The lead(II) ion is covalently linked with a chelated En molecule (Pb-N 2.46–2.48 Å) and I^? anions (Pb-I 3.087–3.343 Å). Covalently bonded atoms form an umbrella-like coordination Pb(II) polyhedron. The side containing the lone electron pair of the lead(II) ion has coordination completed by two I^? anions of neighbouring molecules with the Pb-I 3.621–3.627 Å.     

Structural Characterization and Thermal Behavior of 1-Amino-1-methylamino-2,2-dinitroethylene

A novel high energetic material, 1‐amino‐1‐methylamino‐2,2‐dinitroethylene (AMFOX‐7), was synthesized through 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) reacting with methylamine in N‐methyl pyrrolidone (NMP) at 80.0°C, and its structure was determined by single crystal X‐ray diffraction. The crystal is monoclinic, space group P2₁/m with crystal parameters of a=6.361(3) Å, b=7.462(4) Å, c=6.788(3) Å, β=107.367(9)°, V=307.5(3) ų, Z=2, µ=0.160 mm^?1, F(000)=168, D_c=1.751 g·cm^?3, R₁=0.0463 and wR₂=0.1102. Thermal decomposition of AMFOX‐7 was studied, and the enthalpy, apparent activation energy and pre‐exponential constant of the exothermic decomposition reaction are 303.0 kJ·mol^?1, 230.7 kJ·mol^?1 and 10^21.03 s^?1, respectively. The critical temperature of thermal explosion is 245.3°C. AMFOX‐7 has higher thermal stability than FOX‐7.     

Photocurrent kinetics at the electron emission from a metal into electrolyte solution: Part II. Solutions without acceptors and solutions of N2O,NO2−, NO3−

A method of measuring the kinetics of currents arising at the electron photoemission from a metal into electrolyte solution when affected by the u.v. laser pulses for 10^?8 s at the frequency of repetitions 10–25 Hz is described. Measurements have been taken in solutions without acceptors and in those containing N₂O and NO₂^?, NO₃^? ions as electron acceptors. The rate constants of capture of the solvated electrons by N₂O ((6±1)×0⁹ mol^?1 s^?1) and NO₂^? ((4.5±1)×10⁹ mol^?1 s^?1) and the diffusion coefficients of OH-radicals ((1.0±0.3)×10^?5 cm² s^?1) and of NO ((1.2±0.3)×10^?5 cm² s^?1) are found. The oxidation rate of NO₃^2? has been shown to decrease from 40 cm s^?1 in the range of potentials ?0.55 to ?1.0 V. The rate constant of bimolecular recombination of the solvated electrons ((1.3±0.4)×10¹⁰ mol^?1 s^?1) has been found from the dependence of the emitted charge on the light intensity.     

A flash photolysis–resonance fluorescence kinetics study of ground-state sulfur atoms. II. Rate parameters for reaction of S(3P) with C2H4

Absolute rate constants for the reaction of S(³P) with ethylene were measured over an ethylene concentration range of 7, a total pressure of 50 to 400 torr, and a flash intensity range of 10. At 298°K, the bimolecular rate constant was found to be invariant over this range of variables and had a measured value of 4.96 × 10^?13 cm³ molec^?1 s^?1. Over the temperature range of 218° to 442°K, the rate data could be fit to a simple Arrhenius equation of the form Units are cm³ molec^?1 s^?1. The dependence of the measured value of k₁ on the concentration of the reaction product ethylene episulfide is discussed.     

Light Energy Collection in a Porphyrin–Imide–Corrole Ensemble

An assembly consisting of three units, that is, a meso‐substituted corrole ( C3 ), 1,8 naphthaleneimide ( NIE ), and a Zn porphyrin ( ZnP ), has been synthesized. NIE is connected to C3 through a 1,3‐phenylene bridge and to the ZnP unit through a direct C? C bond. The convergent synthetic strategy includes the preparation of a trans‐A₂B‐corrole possessing the imide unit, followed by Sonogashira coupling with a meso‐substituted A₃B‐porphyrin. The photophysical processes in the resulting triad ZnP-NIE-C3 are examined and compared with those of the corresponding C3-NIE dyad and the constituent reference models C3 , NIE , and ZnP . Excitation of the NIE unit in C3-NIE leads to a fast energy transfer of 98 % efficiency to C3 with a rate k_en=7.5×10¹⁰ s^?1, whereas excitation of the corrole unit leads to a reactivity of the excited state identical to that of the model C3 , with a deactivation rate to the ground state k=2.5×10⁸ s^?1. Energy transfer to C3 and to ZnP moieties follows excitation of NIE in the triad ZnP-NIE-C3 . The rates are k_en=7.5×10¹⁰ s^?1 and k_en=2.5×10¹⁰ s^?1 for the sensitization of the C3 and ZnP unit, respectively. The light energy transferred from NIE to Zn porphyrin unit is ultimately funneled to the corrole component, which is the final recipient of the excitation energy absorbed by the different components of the array. The latter process occurs with a rate k_en=3.4×10⁹ s^?1 and 89 % efficiency. Energy transfer processes take place in all cases by a Förster (dipole–dipole) mechanism. The theory predicts quite satisfactorily the rate for the ZnP/C3 couple, where components are separated by about 23 Å, but results in calculated rates that are one to two orders of magnitude higher for the couples NIE/ZnP (D/A) and NIE/C3, which are separated by distances of about 14 and 10 Å, respectively.     

X-ray diffraction investigations of the structure of concentrated ionic solutions

A liquid-type quasi-close-packing of molecular aggregates [In(NO₃)₂(H₂O)₄]⁺ is suggested as a model to interpret the scattered X-ray intensity of 2.27, 1.30, and 3.96 M aqueous solutions of indium nitrate; but the existence of another packing in the less concentrated solutions may not be excluded. Three different molecular models were tested to obtain agreement between the observed and calculated intensity, from s = (4π/λ)sinθ ≈ 0.7 to 13.0 Å⁻¹ for 2.27 and 1.30 M aqueous solutions.     

Gas electron diffraction: the direction of development of the method

The problems of gas phase electron diffraction experiments are considered. The operating conditions for a reconstructed electron diffraction apparatus are determined in a scattering regime with an effective cross section of σ = 1.06 × 10² b on a molecular beam with Kn > 1. On the example of the I₂ molecule it is shown that at a vapor pressure over a substance equal to 10^?3 mmHg, one can sort out a desired signal at scattering angles up to s = 30 Å^?1. A nomographic chart for the choice of the optimal operating conditions of electrons scattering is proposed.     

Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5-trioxane between 290 and 600 K

Absolute rate constants are measured for the reactions: OH + CH₂O, over the temperature range 296–576 K and for OH + 1,3,5-trioxane over the range 292–597 K. The technique employed is laser photolysis of H₂O₂ or HNO₃ to produce OH, and laser-induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH₂O) = (1.66 ± 0.20) × 10^?11 exp[?(170 ± 80)/RT] cm³ s^?1 and k(1,3,5-trioxane) = (1.36 ± 0.20) × 10^?11 exp[?(460 ± 100)/RT] cm³ s^?1. The transition-state theory is employed to model the OH + CH₂O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH₂O) = 1.2 × 10^?18 T^2.46 exp(970/RT) cm³ s^?1. An estimate of 91 ± 2 kcal/mol is obtained for the first C? H bond in 1,3,5-trioxane by using a correlation of C? H bond strength with measured activation energies.