The rate constants of the gas-phase reactions K + Cl ⇆ K+ + Cl− and KCl + M ⇆ K+ + Cl− + M from measurements in atmospheric pressure flames

Mass spectrometric studies of the ions present in H₂/O₂/N₂ flames with potassium and chlorine added have demonstrated that ionization can occur in the forward steps of K + Cl ? K⁺ + Cl^? (II), KCl + M ? K⁺ + Cl^? + M (IV), where M is any third body. Variations of [K⁺] with time in these systems have been measured and establish that the rate coefficients (in ml molecule^?1 s^?1) of the ion-producing steps are k₂ = 5 × 10^?10T^{?$\text{1}\text{2}$} exp(?10 500/T) and k₄ = 2.2 × 10⁷T^?3.5 × exp(?60 800/T). Coefficients for ion-ion recombination have been obtained from k₂ and k₄ using the equilibrium constants of (II) and (IV) and are k_?2 = 1.7 × 10^?9T^{?$\text{1}\text{2}$} and k_?4 = 1.1 × 10^?17T^?3, with each one in the ml molecule^?1 s^?1 system of units. Replacement of the N₂ in one of these flames with sufficient Ar to maintain the temperature constant leaves the measured k₂ and k_?2 unchanged, but lowers the observed k₄ and k_?4. This confirms that ion-recombination in the backward step in (II) is a two-body process, whereas in (IV) it is termolecular.     

Studies with dithizone: Part XXI. The Relationship between pH12 and Molar Solubility

The effect of changes of ionic strength on the partition of an analytically important weak acid between a variety of aqueous and immiscible organic phases has been studied with respect to new measurements on dithizone (3-mercapto-1,5-diphenylformazan) and di(p-tolyl)thiocarbazone. A linear relationship has been deduced between the pH at which 50% extraction takes place and S_r,o (the solubility of the reactant in the organic phase), and confirmed by measurements of pH_{$\text{1}\text{2}$}, and S_r,o for a large number of organic solvents. The solubilities of the reagents in water, S_r, are also reported. The form of the relationship between pH and log D, and between pH_{$\text{1}\text{2}$} and log S_r,o is the same whether a solution of dithizone consists of a single species or a mixture of thiol and thione forms in tautomeric equilibrium.     

Etude par diffraction de neutrons de la phase Sr0,5La1,5Li0,5Fe0,5O4

A neutron diffraction study has been carried out on Sr_0.5La_1.5Li_0.5Fe_0.5O₄ of K₂NiF₄-type derived structure and it has shown that iron in the tetravalent state has a high spin configuration (t³_2ge¹_g) and that the material has some stacking defects. At room temperature this compound shows an ordering between iron and lithium atoms leading to a nuclear cell a₀√2, a₀√2, c₀ (a₀ and c₀ are the parameters of the K₂NiF₄-type cell). At low temperature ($\text{T <}\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}$) the magnetic structure can be described as antiferromagnetic, corresponding likely to a colinear pattern with a propagation vector of 0.5 ($\text{2π}\text{a}{}_0$) along the [110] axis. At higher temperature ($\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}\text{< T < T}{}_{\mathrm{<mtext>N</mtext>}}$) helimagnetic structure is consistent with a propagation vector of 0.47 ($\text{2π}\text{a}{}_0$) [110].     

Phase equilibria and thermodynamics of coexisting phases in rare-earth element-iron-oxygen systems. I. The cerium-iron-oxygen system

In the present work it is shown that in the CeFeO system only one ternary compound with a perovskite structure, the orthoferrite CeFeO₃, is formed. We define the crystallographic properties of cerium ferroperovskite more accurately. The thermodynamics of its oxidation and reduction over a temperature range of 900–1200°C are studied using the emf method with a solid electrolyte.It is shown that the free energy of cerium orthoferrite formation from the oxides according to the reaction $\text{1}\text{2}\text{Ce}{}_2\text{O}{}_3\text{+}\text{1}\text{2}\text{Fe}{}_2\text{O}{}_3\text{=}\text{CeFeO}{}_3$, derived from data on the equilibrium oxidation of CeFeO₃, differs very little from the value of ΔG°, calculated from the magnitude of the equilibrium pressure of oxygen over the orthoferrite and reduction products coexisting with it.Phase equilibria and the thermodynamics of coexisting phases in the CeFeO system have been investigated. Equilibrium diagrams are constructed which define the character of the changes taking place in the CeFeO system during changes in partial oxygen pressure, temperature, and composition of the initial oxide mixture. Thus, we have equilibrium diagrams of the type P_O2 = f(composition) with T = constant; with one composition parameter fixed; and T = f(composition) with P_O2 = constant.     

Phase equilibria and thermodynamics of coexisting phases in rare-earth element-iron-oxygen systems. II. The praseodymium-iron-oxygen system

The phase equilibria and the thermodynamics of coexisting phases in the PrFeO system have been studied using static and dynamic methods for attaining equilibrium with subsequent annealing and identification of the condensed phases by X-ray analysis. Equilibrium phase diagrams have been constructed to define the changes that take place in the PrFeO system on variation of the partial oxygen pressure, the temperature, and the composition of the initial mixture of oxides. An isothermal cross section at 1300°K and equilibrium diagrams of the type P_O2 = f(composition) with with one composition parameter fixed and T = f(composition) with P_O2 = constant have been constructed. It has been shown in the PrFeO system that only one ternary compound with perovskite structure, PrFeO₃, is formed, and furthermore, it is stable no matter how high the partial oxygen pressure.     

Gradient expansion of the atomic kinetic energy functional

It is demonstrated that the ground-state atomic kinetic energy functional T[?], where ? is the electron density, can be computed to surprising accuracy from the truncated gradient expansion: T[?] = + T₂[?] + T₄[?], with T_o[?] = $\text{3}\text{10}$(3π²)$\text{2}\text{3}$ ∫ ?$\text{5}\text{3}$ d_τ, T₂ [?] = $\text{1}\text{72}$ ∫ (??)²?^?1 d_τ, and T₄ [?] given by the formula of Hodges. Calculations of T₀, T₂ and T₄ are reported for He with ? both the Hartree—Fock and a very accurate density, and for Ne, Ar and Kr with ? the Hartree—Fock density. For Kr, T₀ + T₂ + T₄ is within 0.3% of the exact Hartree—Fock T, with T₂/T₀ = 0.05, T₄/T₂ = 0.17.     

Magnetic superexchange involving tetrahedral anions: One-dimensional antiferromagnetic interactions via sulfate anions in M(2,9-di-CH3-1,10-phenanthroline)SO4 (M = Mn,Fe, Co,Ni, Cu)

The magnetic susceptibilities of powder samples of the polymeric compounds M(dmp)SO₄ (M = Mn, Fe, Co, Ni, Cu; dmp = 2,9-di-CH₃-1,10-phenanthroline) have now been studied at temperatures between 1.5 and 305 K. There is clear evidence of one-dimensional, antiferromagnetic interactions in the Mn, Fe, Co, and Ni compounds: from $\text{T ? 300}\text{to}\text{1.7}\text{K}$, the magnetic moment decreases steadily from a value that is approximately the spin-only moment of the high-spin configuration to a value that is ～20% of the spin-only moment, and the susceptibility-vs-temperature curve contains a broad maximum atT ≤ 30 K. Cu(dmp)SO₄, however, exhibits almost perfect Curie-Weiss paramagnetism. These results when combined with the results of various spectroscopic studies lead to proposed molecular structures (chainlike polymers of cis-MN₂O₄ chromophores and bridging-chelating sulfates) and estimated energies of intrachain antiferromagnetic exchange ($\text{?0.5}\text{K}\text{≥}\text{J}\text{k}{}_{\mathrm{<mtext>B</mtext>}}\text{≥ ?10}\text{K}$).     

Isotope effects in electron-donor-acceptor complexes involving aromatic hydrocarbons and fluoranil from NMR shift measurements

Equilibrium constants and NMR shift parameters have been determined for complexes of benzene, toluene and p-xylene and their perdeutero-analogues with fluoranil in cyclohexane solution from NMR shift measurements. Isotope effects are observed in the 1:1 equilibrium constants for the complexes of p-xylene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$= 1.1₀) and toluene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$ = 1.0₉). A much smaller effect was observed for the benzene complex which could not be quantified. These results may be interpreted through either the larger electronegativity of H over D, or the greater steric requirements of H over D.     

Dissolution of Ca3(AsO4)2 · 2H2O in the system CaOAs2O5H2O at 35, 40, 45 and 50°C and the related thermodynamic data

Calcium arsenate dihydrate is precipitated at pH 7.0 and its dissolution in aqueous solutions at temperatures of 35, 40, 45 and 50°C and a pH of between 3.0 and 8.0 is investigated. The thermodynamic parameters ΔG⁰, ΔS⁰ and ΔH⁰ for the process are evaluated. Temperature dependence of solubility is obtained by the equations ?log K_TCA = $\text{9078.138}\text{T}$ ? 34.0468 + 0.0821421 T     

Radiation postpolymerization in devitrifying matrices: Different polymerization activity of acrylic and methacrylic monomers

Investigation of the effect of the α-CH₃-group on low-temperature postpolymerization in devitrifying matrices leads to the following conclusions. 1. The low-temperature postpolymerization in supercooled alcohol solutions (T_g ～ 102 K) is quite efficient with acrylic monomers. Inactivity of their methacrylic analogues under these conditions is attributed to steric screening of the unpaired electron in the growing radicals. 2. As the temperature is raised and the CH₃-group vibration intensity increases, the screening effect fades. Thus in devitrifying water-alcohol solutions of NaAA and NaMAA, at higher temperatures the postpolymerization is efficient in both cases. Data on copolymerization of NaAA and NaMAA indicate that at ～ 170 K the steric limitations due to the CH₃-group are eliminated. 3. In a glycerine matrix ($\text{T}{}_{\mathrm{g}}\text{? 195 K}$), all the acrylic and methacrylic monomers studied show efficient polymerization over virtually the same temperature range. It is concluded that the a-CH₃-group in methacrylic monomers appreciably affects their polymerization activity only at low temperatures, where steric screening of the growing polymer radical becomes important.     

Non-condon effects on radiationless triplet decay in benzene and naphthalene

Model calculations that avoid the Condon approximation are reported for T₁$\text{}\text{?}$ar S₀ intersystem crossing in normal and perdeuterated benzene and naphthalene. In both benzenes and in naphthalene-d₈, skeletal bending vibrations coupling T₁ to T₂ are found to be more efficient as accepting modes than CH-stretching vibrations.     

The ring-opening reactions of propylene oxide with chloroacetic acids

The association constants, k_d, of dichloroacetic acid (DCA) with ethers (tetrahydrofuran, tetrahydropyran, dibutyl ether, 1,4-dioxane) were measured in CCl₄ from 20°–40° using near IR spectra. A linear relationship between log₁₀K_D and log₁₀K_p was found, where K_p was the association constant of phenol with ethers. On the basis of their relationship the association constants of DCA with propylene oxide (PO) were estimated from those of phenol with PO. Furthermore, the ring-openings of PO with chloroacetic acids (trichloroacetic acid (TCA) or DCA) were studied kinetically in toluene. It was found that the PO-TCA reactions obeyed the second-order kinetics dependent on the first order both in the PO concn and in the TCA concn, and that the PO-DCA reactions obeyed the third-order kinetics on the first order in the PO concn and on the second order in the DCA concn. The elementary reaction rate constants were estimated on the basis of measured rate constants and estimated equilibrium constants and activation enthalpies were obtained from their temp dependence to be 13.5 $\text{kcal}\text{mol}$ in the PO-TCA reaction and 19.7 $\text{kcal}\text{mol}$ in the PO-DCA reaction. The mechanism was based on the activation enthalpy of elementary reaction and it was concluded that the main factor governing the reaction was the extent of activation of the protonated oxirane (the extent of polarization of the C-O bond in the oxirane ring).     

Determination of the vapour pressures of o-, m-, and p-dinitrobenzene by the torsion-effusion method

The vaporization of o-, m-, and p-dinitrobenzenes was investigated by means of the torsion-effusion method and the selected equations for vapour pressure p as a function of temperature T are:

$\text{o-dinitrobenzene: log}{}_{10}\text{(}\text{p}\text{atm}\text{)=(7.03±0.34)?(4270±120)}\text{K}\text{T}\text{,m-dinitrobenzene: log}{}_{10}\text{(}\text{p}\text{atm}\text{)=(7.66±0.28)?(4400±100)}\text{K}\text{T}\text{,p-dinitrobenzene: log}{}_{10}\text{(}\text{p}\text{atm}\text{)=(8.34±0.34)?(4860±120)}\text{K}\text{T}$

The sublimation enthalpies ΔH^o(o-, 298.15 K) = (21.0 ± 0.5) kcal_th mol^?1, ΔH^o(m-, 298.15 K) = (20.8 ± 0.2) kcal_th mol^?1, and ΔH^o(p-, 298.15 K) = (23.0 ± 0.6) kcal_th mol^?1, are also derived by means of the second- and third-law treatments of the results.     

Crystallographic studies on cation substitutions in the system (Na,K) (V,P)O3

Three compounds in the system (Na,K) (V,P)O₃ were synthesized and their structures were refined by full matrix least squares method in the space group $\text{C2}\text{c}$. Their compositions were shown by site population analysis to be Na(V_0.66P_0.34)O₃ (I), (Na_0.88K_0.12)VO₃ (II), and (Na_0.5K_0.5)VO₃ (III). All are related to the structure of α-NaVO₃ which in turn is related to the clinopyroxene structure characterized by infinite chains of SiO₄ tetrahedra sharing vertices and two inequivalent metal cation sites M1 and M2. Both sites feature sixfold coordination in compounds I and II, while the Na and K are ordered into M1 and M2 sites, respectively in III, with the latter showing eightfold coordination. The pentavalent cations are randomly distributed in tetrahedral sites in I, and in II the K was found to occupy the M2 sites only. Changes in the α-NaVO₃ structure upon cation substitution are discussed in terms of rotation and displacement of the tetrahedral chains. Parameters for measuring these chain movements are proposed and found to exhibit an almost linear relationship with the ratio $\text{〈X?0〉}\text{〈M2?0〉}$ in cases where the M1 site is exclusively occupied by Na.