Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1974"

Site-binding model of the electrical double layer at the oxide/water interface

Abstract: A site-binding model of the oxide/aqueous electrolyte interface is introduced, in which it is proposed that the adsorbed counter ions form interfacial ion pairs with discrete charged surface groups. This model is used to calculate theoretical surface charge densities of the potential-determining (H+/OH–) ions and the potential at the Outer Helmholtz Plane, which are shown to be consistent with experimental data for oxides. An explanation is provided for the difference between silica and most other oxides in terms of the dissociation constants of the surface hydroxyl groups.

Spontaneous rupture of thin liquid films

Abstract: The rupture of a liquid film on a solid surface and of a free liquid film have been studied using hydrodynamic stability theory. The films are not thicker than several hundred Angstrom. A small perturbation applied to the free interface generates motions in the film, and the assumption is made that the Navier–Stokes equations can be used to describe them. The difference in forces acting upon an element of liquid in a thin film and in a bulk fluid is accounted for by introducing a body force in the Navier–Stokes equations. This force is calculated from the potential energy per unit volume in the liquid caused by the London–van der Waals interactions with the surrounding molecules of the liquid and with those of the solid. If the perturbation grows, it leads to the rupture of the film. The range of wavelengths of the perturbation for which instability occurs is established and the time of rupture is evaluated. The effect of insoluble and soluble surface active agents is analyzed. Available experimental data concerning condensation on a solid surface and coalescence of bubbles are explained on the basis of the obtained results.

Transition state treatment of the relative viscosity of electrolytic solutions. Applications to aqueous, non-aqueous and methanol + water systems

Abstract: A transition-state treatment of the relative viscosity of electrolyte solutions is described. The following expression is found for the viscosity B-coefficient: B=(text-decoration:overlineV°1–text-decoration:overlineV°2)/1000 +text-decoration:overlineV°1[(Δµ°[graphic omitted]2–Δµ°[graphic omitted]1)/1000 RT]. text-decoration:overlineV°1 and text-decoration:overlineV°2 are the partial molal volumes of the solvent and solute respectively; Δµ°[graphic omitted]1 is the activation energy for viscous flow of the solvent, and Δµ°[graphic omitted]2 the “ionic activation energy” at infinite dilution.For aqueous solutions, at 25°C, the term (text-decoration:overlineV°1–text-decoration:overlineV°2)/1000 accounts completely, in the case of ammonium chloride, and partially in the case of potassium, rubidium and caesium chlorides, for the negative sign of the B-coefficient. When solutions in different solvents are compared, the well-known tendency for B to increase with text-decoration:overlineV°1 is at least partly explained by the form of the above expression; changes in µ°[graphic omitted]2 from water to methanol, for example, are less dramatic than changes in B. B-coefficients in the methanol + water system are consistent with a maximum in solvent structure around 20% methanol (w/w) at 25°C; whilst the µ°[graphic omitted]2-values support this interpretation, it is noted that solvent structure can influence B twice over, in µ°[graphic omitted]2 and (trivially) in µ°[graphic omitted]1.

New analytic form for the potential energy curves of stable diatomic states

Abstract: An analytic potential for stable states of diatomic molecules is proposed V=–De(1 +a1r+a2r2+a3r3)e–a1r. The constants a1, a2 and a3 are obtained from the harmonic, cubic and quartic force constants. The potential is shown to be superior to the Hulburt–Hirschfelder potential when tested on a least-squares basis against the spectroscopic RKR potential.

Thermodynamic effects of orientational order in chain-molecule mixtures. Part 1.—Heats of mixing of globular and normal alkanes

Abstract: Heats of mixing at 25°C have been obtained calorimetrically for alkane mixtures where component 1 is cyclohexane, 2,2-dimethylbutane or n-hexane and component 2 is a normal-Cn, n= 6,8,12 or 16, or a corresponding branched-Cn: 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-penta-methylheptane or 2,2,4,4,6,8,8-heptamethylnonane. For the three n-Cn series, the molar heats and heats per unit volume are positive and increase rapidly with n. With the branched-Cn, cyclohexane gives smaller positive heats decreasing with n, while n-hexane and 2,2-dimethylbutane show increasingly negative heats. The magnitudes and variations of the heats, and of the derived X12 parameters are inconsistent with the usual interpretation of positive ΔHM in n-alkane mixtures, i.e. an energetic weakness of methyl(end)-methylene (middle) interactions. The results are explained by energetic effects associated with a correlation of molecular orientations (CMO) in the pure components and the mixture. The CMO, studied optically by Bothorel and collaborators, is highly sensitive to molecular shape, increasing with n for pure n-Cn liquids, remaining zero for the branched-Cn, and being destroyed on mixing with spherical molecules such as cyclohexane and 2,2-dimethylbutane. Parameters (J), characterizing the CMO in the component liquids, are used to give a quantitative interpretation of the X12 and ΔHM values.

Assignment of the charge-transfer bands in some metal phthalocyanines. Evidence for the S= 1 state of iron (II) phthalocyanine in solution

Abstract: Magnetic circular dichroism spectroscopy has been used to investigate the assignment of the charge transfer bands in a number of metal phthalocyanines containing first row transition metals. It has been shown that the band in cobalt(III) phthalocyanine dicyanide at 22.5 kK is not a charge transfer band but must be a transition of the phthalocyanine ring. Similarly doubt is shed upon the charge-transfer assignment of the band in iron(II) phthalocyanine dicyanide at 22.5 kK. However, it has been confirmed that the band system in cobalt(I) phthalocyanine at ∼22 kK is a metal-ligand charge-transfer transition which may be assigned as eg→b1u, b2u. Finally, the low energy band of iron(II) phthalocyanine which appears in solvents of low co-ordinating ability, such as dichlorobenzene, has been studied. The m.c.d. spectrum enables a choice to be made for the ground state of the compound. It is shown to be 3A2g, a result which is the first demonstration of an intermediate spinstate of iron(II) in solution. The low energy band in the spectrum has been assigned as a metal to ligand charge transfer band, 3A2g→3Eu. This evidence throws considerable doubt upon the recent assignment of the ground state of crystalline iron(II) phthalocyanine to 3B2g based upon single crystal anisotropy measurements.

Use of the Langmuir method for kinetic studies of decomposition reactions: calcite (CaCO3)

Abstract: The Langmuir method for measurement of vapour pressures has been tested for use in studies of decomposition reactions. The isothermal weight loss in vacuum from cleavage (10text-decoration:overline11) planes of calcite (CaCO3) single crystals was measured continuously at temperatures from 934 to 1013 K. The rate was constant until approximately 80% of a 1 mm slice had decomposed. The apparent activation enthalpy was 205 kJ (49 kcal) mol–1. Micrographic examination showed an approximately 30 µm thick layer, probably a metastable form of calcium oxide, separating the calcite from the growing layer of oriented stable calcium oxide. The 30 µm layer yielded a single X-ray diffraction peak which was displaced slightly from the strongest (220) peak of the oriented normal calcium oxide. Lower apparent activation enthalpies measured in previous studies of calcite decomposition in inert atmospheres are suggested to result either from partial diffusion control of the process or from catalysis of the direct formation of normal calcium oxide by carbon dioxide or a component of the system atmosphere. The ratio of the measured decomposition rate in vacuum to the maximum rate, which can be calculated from the Hertz–Knudsen–Langmuir equation, is suggested to be a useful parameter in correlating and predicting decomposition reaction rates.

Measurement and prediction of equilibrium ratios for the C2H6+ CO2 system

Abstract: Isothermal vapour/liquid equilibrium compositions and pressures are determined for the C2H6+ CO2 system, which is known to form a minimum boiling azeotrope. A vapour recirculation apparatus was used in obtaining experimental data for the –50.00, –30.00, –10.00, +10.00 and +20.00°C isotherms.A model based on a statistical mechanical formulation of the principle of corresponding states is used to predict equilibrium ratios for the system under investigation. The model contains two temperature independent parameters and is found to represent the data extremely well.

Calculation of the geometries of binary transition metal carbonyl and dinitrogen complexes

Abstract: A simple molecular orbital method is used to calculate the minimum internal energy (MIE) structures of binary transition metal carbonyls and dinitrogen complexes. Agreement with the experimentally determined geometries of M(CO)x(x= 2–6, M =d5 to d10 metal) is excellent. The change in energy of the predominantly metal d orbitals with geometry (Walsh diagrams) are shown to be metal–ligand overlap integral determined and the calculated MIE geometries are readily rationalised by Jahn–Teller considerations and the use of the Walsh diagrams.

Ion-exchange selectivity and electrolyte concentration

Abstract: It is shown how, from a given exchange isotherm at a given total solution normality, one may calculate isotherms and exchange selectivity coefficients at other total normalities. When the exchange ions have different valences the isotherms depend strongly upon the total normality, and the selectivity of the exchanger, for the ion of higher valence increases without limit with increasing dilution. Also when the ions have different valences isotherms without inflexion points can become sigmoid with increasing dilution and sigmoid isotherms can loose their inflexions. In these circumstances sigmoid isotherms, for example in zeolites, cannot provide evidence that there is more than one kind of exchange site in the exchanger. However, the changes in isotherm shape or position with dilution are very small when the ions have the same valence. A way of diagrammatic representation of isotherms has been described which is independent of electrolyte concentration.

Infra-red study of phosphate adsorption on goethite

Abstract: Infra-red spectra of phosphate adsorbed on synthetic goethite (α-FeOOH) show only PO3–4 ions to be present. Phosphate bands observed at about 1125, 1050 and 1000 cm–1 are shifted to 1190, 1100 and 1000 cm–1 following the removal of physically adsorbed H2O or D2O. Comparison of the spectra with model systems suggests that the high frequencies observed for the ν3 vibration of phosphate in evacuated samples arise from binuclear coordination (coordination of two oxygen atoms of a phosphate group to two surface Fe ions) to Fe3+ on the surface. Binuclear sites on the predominant (100) and (010) faces are due to the unshared apices of adjacent Fe octahedra. Spectral changes due to physically adsorbed water in non-evacuated samples are attributed to strong hydrogen bonding to one of the free phosphate oxygens.

Rate measurements of reactions of OH by resonance absorption. Part 3.—Reactions of OH with H2, D2 and hydrogen and deuterium halides

Abstract: The rates of the reactions of OH with H2, D2, HCl and DCl have been determined between 210 and 460 K using time-resolved resonance absorption to monitor removal of OH following creation of the radicals by flash photolysis of mixtures containing H2O or N2O + H2. Arrhenius rate laws are obeyed by all four of these reactions throughout this range of temperature: kOH + H2= 1.8 × 10–11 exp[–19.4 kJ mol–1/RT] cm3 molecule–1 s–1, kOH + D2= 1.25× 10–11 exp[–21.5 kJ mol–1/RT] cm3 molecule–1 s–1, kOH + HCl= 4.1 × 10–12 exp[–4.4 kJ mol–1/RT] cm3 molecule–1 s–1, kOH + DCl= 4.7 × 10–12 exp[–6.5 kJ mol–1/RT] cm3 molecule–1 s–1.The observed kinetic isotope effects are compared with predictions based on 3- and 4-atom models of the transition states using semi-empirical potential functions to estimate the transition state properties. Preliminary measurements on the reactions of OH with HBr and HI are also reported. The rate constants at 298 K are respectively 4.5 × 10–12 and 9 × 10–12 cm3 molecule–1 s–1.

Kinetic study of electronically excited nitrogen atoms, N(22DJ, 22PJ), by attenuation of atomic resonance radiation in the vacuum ultra-violet

Abstract: The collisional behaviour of electronically excited nitrogen atoms, N(22DJ,22PJ), has been investigated by atomic absorption spectroscopy using time-resolved attenuation of resonance radiation in the vacuum ultra-violet. The optically metastable atoms have been generated by the repetitive, pulsed irradiation of nitrous oxide in the Schumann region and the resulting photoelectric pulses representing the concentration profiles of the atomic states have been signal averaged. This system has involved the use of a rapid response logarithmic signal converter, capable of measuring directly in (I0/Itr) for a weak, fast decaying signal. This has permitted quenching rate constants to be determined with an accuracy considerably improved upon those obtained previously from “single-shot” measurements. Deactivation rate constants are reported for N(22DJ) and N(22PJ) with the gases H2, N2, O2, CO, NO, CO2 and N2O and compared with those from earlier determinations.

Protein–surfactant interactions. Nuclear magnetic resonance and binding isotherm studies of interactions between bovine serum albumin and sodium dodecyl sulphate

Abstract: The interactions between the protein, bovine serum albumin (BSA), and sodium dodecyl sulphate (SDS) at pH 5.6 have been studied by n.m.r. spectroscopy. The main findings are (i) above binding numbers of about 10–20, SDS molecules are in a micelle-like environment formed with apolar (and polar) groups of the protein, (ii) both the surfactant head groups and alkyl chains are associated with the protein at the initial ten binding sites, and (iii) when the protein is denatured by SDS much of the secondary and tertiary structure remains intact, including the initial binding sites.

Polar solvent structure in the theory of ionic solvation

Abstract: The description of ionic solvation in terms of modern electrodynamics of condensed media with spatial dispersion enables us rigorously to take account of the structure of a polar solvent. The basic physical principles of the dielectric formulation of polar systems are considered. On this basis the phenomenological theory of ionic solvation, which involves the collective interactions of the solvent particles and the statistical character of the structure of the solvent, is developed. It is shown that the free energy of solvation is less than given by the Born formula, due to the correlation of polarization fluctuations in space; these correlations are defined by the characteristic correlation ranges. It is shown that the so-called effective decrease of the dielectric constant near the ion in solvation phenomena may follow as a consequence of the structure of a pure liquid without taking dielectric saturation into consideration. A theoretical basis is given to the phenomenon of the reduction of the solvation of the solute with the strengthening of the structure of a pure solvent. The expression for the free energy of Born charging differs considerably from the Born formula; however, it reduces to the Born formula when the ionic radius is much greater that all the correlation ranges in the solvent. An analytic expression for the free energy of solvation is obtained on the basis of resonable approximations. To compare the theory with experiment, the hydration of a alkali cations and halide anions is considered. The single-ion free energies of hydration are calculated and compared with the experimental free energies for the alkali halide hydration at infinite dilution. Without use of adjustable parameters the results are essentially in quantitative agreement with experiment.

Thermodynamics of the high temperature adsorption of some permanent gases by porous carbons

Abstract: This paper presents precise experimental data for the adsorption (na) of nitrogen and the noble gases by two unactivated and two activated (10.8% and 22.0% burn-off) Saran type porous carbons over the temperature range 0–125°C and at pressures (p) up to 1 atm. The data are analysed in terms of virial type expansions of (i)na/p as a function of p and (ii) ln na/p as a function of na. The number of terms required in each equation to give an adequate representation of the data was determined for each system at each temperature by statistical analysis. Expansion (ii) was found to be superior in the sense that where there was a difference between the number of terms required, expansion (ii) required fewer terms than (i). These differences become more marked for the adsorption of the heavier gases at the lower temperatures. Henry's law constants obtained from (i) and (ii) were, however, in good agreement.The Henry's law constants and their temperature dependence were used to calculate differential enthalpies and standard differential entropies of adsorption (taking na= 10–3 mol g–1 as standard state) in the limit of ideal behaviour. Activation of the carbons decreased the Henry's law constants per unit surface area, and also the magnitude of the enthalpy of adsorption. The standard differential entropy of adsorption increases with activation, reflecting the larger “free volume” available to the adsorbed molecules which may be measured approximately either by the increase in micropore volume or by the increase in the monolayer equivalent surface area.

Gas phase electron diffraction study of six fluoroethylenes

Abstract: Gas phase electron diffraction patterns were analyzed and molecular structures for vinyl fluoride, trans-1,2-difluoroethylene, cis-1,2-difluoroethylene, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene were derived from these data. Structural parameters were obtained by least squares fitting of the calculated to the experimental molecular scattering functions, allowing for simultaneous variation of the non-correlated parameters. A statistical procedure was used to evaluate error limits for the correlated parameters. Moments of inertia computed from the currently reported interatomic distances are in agreement with those derived from microwave spectra. It was found that the measured CC distances correlate with reported vibrational force constants, and the pertinent bond angles are consistent with observed dipole moments.

Evidence for short-range orientation effects in dipolar aprotic liquids from vibrational spectroscopy. Part 2.—Carbonyl compounds

Abstract: In the Raman spectrum of pure liquids, the anisotropic component of the CO stretching band falls at a higher frequency than the isotropic component In the same liquids the infra-red band maximum appears at almost the same frequency as the Raman anisotropic component In some cases the infra-red band may be resolved into two components, the stronger coinciding with the anisotropic, the weaker with the isotropic Raman band These effects disappear with dilution and are reduced with increasing temperatureThis behaviour is explained in terms of a model which assumes that dipolar aprotic liquids are composed of clusters of molecules oriented in an (at least partially) ordered way

Vacuum ultraviolet photoelectron spectroscopy of transient species. Part 4.—Difluoromethylene and ozone

Abstract: He I and He II spectra are reported for the isoelectronic molecules CF2 and O3. New values are reported for the first and higher ionization potentials. The spectra are interpreted with the aid of semi-empirical molecular orbital calculations.

Hydrogen bond strengths and acidities of hydroxyl groups on silica–alumina surfaces and in molecules in solution

Abstract: The properties of hydroxyl groups on mixed silica–alumina gels (0–50 % Al2O3) have been studied by adsorbing weak H bond accepting molecules onto the gels and recording the OH stretching infrared band.Additional measurements on silica gel and compilation of numerous literature data have shown that frequency shift measurements, or series of Δtext-decoration:overlinevOH measurements condensed into BHW (Bellamy, Hallam and Williams) slopes, provide a reliable estimate of the OH acidity. The resulting scale is independent of the atom to which the hydroxyl is attached; it may be used for surfaces of solids as well as for solutions.The results obtained for silica–alumina show that two distinct populations of hydroxyl groups are present. Hydroxyl groups of type 1 are identical with those present on the surface of silica. The spectra show the presence of hydroxyl groups of a second type, the proportion of which increases as the Al content of the gel rises; their acidity corresponds to a pKa between –4 and –8 and they are presumably the sites responsible for the protonation observed upon adsorption of pyridine or ammonia.

Proton and deuteron mobility in normal and heavy water solutions of electrolytes

Abstract: Proton and deuteron mobility in normal and heavy water solutions of some alkali halides (NaCl, KCl, KBr and Kl) and tetra-alkylammonium bromides (where alkyl is Me, Et, Pr or Bu) is measured polarographically and the diffusion coefficients calculated from a corrected Ilkovic equation. The results are analysed in terms of the effect of electrolyte concentration on the excess or Grotthuss mobility of the hydrogen and deuterium ion. The results raise some questions about the accepted mechanism for the transport of the proton and deuteron in solution.

Phase structure, nuclear magnetic resonance and rheological properties of viscoelastic sodium dodecyl sulphate and trimethylammonium bromide mixtures

Abstract: The phase diagram of octyltrimethylammonium bromide and sodium dodecyl sulphate (SDS) in water ( > 90 %) is reported at 298 K; the phase regions observed are liquid, two liquid, and liquid plus liquid crystal. Liquids with viscoelastic properties occur close to the SDS rich liquid boundary, and a correlation is observed between the surfactant n.m.r. linewidths and the rheological properties of these liquids. The most likely explanation of these effects is one involving the occurrence of both cylindrical and spherical micelles, but the possibility that the viscoelasticity is due to the presence of a microemulsion can not be excluded.

Graphical method for factorizing secular determinants of Hückel molecular orbital theory

Abstract: A graphical method is given for simplifying the solution of Huckel's secular equations for molecules with symmetrically-placed atoms.

Kinetics of micellization from ultrasonic relaxation studies

Abstract: The kinetics of micelle formation for a range of ionic surfactants in aqueous solution have been investigated using the ultrasonic relaxation technique. In order to understand the concentration dependance of both the relaxation time and the relaxation strength, and other aspects of the relaxation data, it was necessary to modify our previous two state kinetic model describing micellisation. In this new theoretical treatment the interchange of the monomers to and from the micelles is assumed to be an adsorption mechanism governed by the fundamental kinetic principles introduced by Langmuir in his adsorption theory. Finally we have reconsidered the origin of the chemical relaxation observed in detergent solutions resulting from temperature- and pressure-jump experiments.

Infra-red studies of reactions on oxide surfaces. Part 2.—Methanol on silica

Abstract: Infra-red spectroscopy has been used to investigate the structure of the chemisorbed species which are formed when CH3OH, CH2DOH, CHD2OH and CD3OH react with silica. Force constant calculations utilizing only the CH and CD stretching modes have been used to show that the strongest spectral features can be assigned to an unsymmetrical surface SiOMe group which has one strong and two weak CH bonds. Some additional spectral features which reversibly grew in intensity with increasing sample temperatures have been assigned to a symmetrical SiOMe species which exists in equilibrium with unsymmetrical SiOMe. It has been suggested that the Infra-red bands of symmetrical SiOMe are probably hot bands arising from transitions from the first vibrationally excited state of the SiOC bending mode such that rapid flipping of the SiOC bond can occur in this excited state.

Density and refractive index of solid layers of noble gases and sulphur hexafluoride

Abstract: The density and refractive index of solid layers of the noble gases (Ne, Ar, Kr, Xe) and SF6 were measured as a function of the condensation conditions such as temperature, growth rate and layer thickness by an interferometric method during growth of the layer on a metal mirror substrate.It is shown, that the density (ρ) and refractive index (n) are strongly dependent on the condensation temperature. For condensation temperatures TK above a certain value Tch, which is characteristic for each gas, ρ and n of the solid layers agree very well with those given in the literature for the bulk crystals. Below Tch however, we find an approximately linear decrease of ρ and n with TK. The changes in ρ and n with TK, which can be as large as 30 % and 14 %, respectively, increase in a characteristic manner within the series Ne, Ar, Kr, Xe, SF6, i.e., with increasing molecular weight. The experiments yield information on the structure of the layers and their aging behaviour. This knowledge is a necessary condition for the quantitative study of matrix isolated atoms or molecules, since their properties depend on their interaction with the matrix.

Triple point of the first monomolecular layer of krypton adsorbed on the cleavage face of graphite. Influence of the structure of this surface on the structure of the first adsorbed layer of rare gases

Abstract: From adsorption isotherms of krypton on graphite measured between 79.24 and 88.46 K in the monolayer domain a two-dimensional triple point of 84.8 ± 0.5 K is determined for this system. Thermodynamic analysis of these isotherms and of the isotherms of xenon on graphite measured by Thomy and Duval suggests that the surface structure plays a prominent role in the formation of dense monolayers on the (0001) face of graphite. To explain the striking difference of behaviour of the two rare gases, two factors have to be taken into account; the height of potential barriers to translation and dimensional incompatibility between the lattices of the bulk adsorbates and of the (0001) face of graphite, the first “solid” layer appearing being in registry with the substrate. A single isotherm of argon on graphite measured at 68.78 K suggests that a more exhaustive study of the Ar + graphite system could be useful in establishing the relative importance of both factors.

Enthalpy of interaction between some globular proteins and sodium n-dodecyl sulphate in aqueous solution

Abstract: The enthalpy of binding of sodium n-dodecyl sulphate (SDS) to serum albumin, ovalbumin and ribonuclease A has been measured by microcalorimetry over the temperature range 18.5 to 32.0°C. The amount of SDS bound to the proteins has been measured over a wide range of SDS concentration by equilibrium dialysis. Changes in protein conformation have been monitored by viscometry. The results are consistent with a mechanism in which SDS binds initially to ionic sites on the protein molecules and initiates chain unfolding. At high binding levels the interaction is predominantly of a hydrophobic nature.

Reaction of hydrogen atoms with ethane

Abstract: The reaction between hydrogen atoms and ethane has been studied in a flow-discharge system over the wide temperature range 503–753 K at pressures between 8 and 16 Torr. The major products are methane and ethane, reformed by methyl recombination. Minor products are propane and ethylene with traces of n-butane.The detailed mechanism has been established and computer calculations have been used to derive the set of best-fit rate parameters which reproduce all the experimental results. The results of this work yield the result k1/cm3 mol–1 s–1= 1014.27 ± 0.13 exp (–40.9 ± 1.6 kJ mol–1/RT); H + C2H6→ H2+ C2H5. (1)A survey of all published data some of which have been revised by us to take account of wrongly assumed stoichiometry in the original work, shows that, over a range of 1000 K, the data can be represented by the Arrhenius expression, k1/cm3 mol–1 s–1= 1014.12 ± 0.09 exp (–39.2 ± 0.9 kJ mol–1RT). There is thus no reason to suppose curvature in this plot as has been suggested.Values of the rate constants for the reactions H + C2H5→ 2CH3(2), CH3+ H → CH4(5), and, H + C2H5→ H2+ C2H4(11), are found to be k2/cm3 mol–1 s–1= 1013.57, k5/cm3 mol–1 s–1= 1012.04 at 8 Torr, 1012.20 at 12 Torr and 1012.34 at 16 Torr and k11/cm3 mol–1 s–1= 1012.23.We have reassessed our earlier data on the reaction of hydrogen atoms with ethylene in the light of the recent “low” values for the rate constant of ethyl recombination. From this, we find values for k2 and k5 at 290 K which are, respectively, lower and higher than the corresponding values in the range 503–753 K. It is shown that the slight temperature dependence observed is consistent with the order of reactions (2) and (5).

Infra-red study of nitric oxide adsorption on magnesium oxide

Abstract: An i.r. study of nitric oxide adsorption on high area MgO (previously degassed at 800°C) at room temperature is reported. The adsorption of NO onto MgO produces i.r. bands at 800–900 cm–1, 1100–1250 cm–1, and 1350–1450 cm–1. These absorption bands were assigned to several surface species: NO–2 ions with various configurations and NO– and N2O2–2 ions, co-ordinated to Mg2+ ions. The adsorption (3.3 × 1013 molecule cm–2, at 10.4 × 103 N m–2 of NO) occurs in limited surface zones.