R. J. Thorn

The thermodynamics of ionization of gaseous oxides; the first ionization potentials of the lanthanide metals and monoxides

The first ionization potentials of the gaseous lanthanide metals and monoxides have been determined by electron impact from the appearance potentials of ionization efficiency curves. A method of simultaneous and intercomparative measurements with known standards was used and the results for the lanthanide metals are in excellent agreement with values obtained previously from spectroscopic and surface ionization studies. In the early part of the lanthanide sequence the ionization potentials of LnO(g) are less than those of Ln(g), whereas the converse is true in the latter part. The differences in the ionization potentials of LnO(g) and Ln(g) are simply related to the differences in the dissociation energies of LnO(g) and LnO+(g). Values of D0(LnO+) are derived. The nature of the chemical bonding in LnO(g) and LnO+(g) is examined for the lanthanide sequence by means of an electrostatic point‐charge model. The assumption of monotonic variation of the interatomic distance and the electrostatic repulsion param...

Nonstoichiometry in Uranium Dioxide

An extension of Andersons formulation of the defect theory of nonstoichiometry is used with an oxygen—interstitial oxygen‐vacancy model to calculate the composition of the uranium dioxide phase at the lower phase boundary and the relative partial molar thermodynamic functions for oxygen at compositions ranging from the lower phase boundary to UO2.08. The model is used as a basis on which to argue that differing experimental results near UO2.00 are more likely due to differing, nonequilibrium, concentrations of uranium vacancies than to failure to reach oxygen equilibrium. The present form of the model, with an interstitial site density of one per uranium site fails sharply at about UO2.08 rather than gradually as the oxygen content is increased from UO2.00. Discussion of the effects of alternate site densities is used to explain the observed values of the partial molar entropy of the oxygen in the range from UO2.02 to UO2.24.

Vaporization Coefficient of Graphite and Composition of the Equilibrium Vapor

Direct comparisons of the rates of evaporation and of effusion from a Knudsen cell yield a value of about 0.15 for the vaporization coefficient of graphite. The absolute effusion rates, taken together with other data, not only confirm the existence of triatomic carbon in the equilibrium vapor but permit the evaluation of the thermodynamic properties of the triatomic vapor. In the region of 2400°K the vapor pressure of the triatomic form is logp3(atmos)=−40296.0T+9.811 which yields 184.4 kcal/mole for the heat of sublimation and 77.41 eu for the entropy of C3. This value for the heat agrees with that obtained in mass spectrometric measurements by Chupka and Inghram. The partial pressures at 2400°K of C1, C2, and C3 are 4.29×10—8, 1.13×10—8, and 1.05×10—7 atmos respectively. A comparison with the mass spectrometric data yields 2.7 for the ratio of the ionization cross section of C3 to C1 and values of 0.37, 0.34, and 0.08 for the individual vaporization coefficients of C1, C2, and C3 respectively. The vapor...

Thermodynamic Properties of Gaseous Yttrium Monoxide. Correlation of Bonding in Group III Transition‐Metal Monoxides

The vapor from solid yttrium sesquioxide contained in a Knudsen cell made of tungsten has been investigated by measuring the absolute effusion rate and by studying the effusate in a mass spectrometer. The latter demonstrates that the gaseous species are yttrium monoxide, oxygen, and a small amount of yttrium. Measurements of the appearance potentials for the ions enable one to conclude that the ratio of monoxide‐to‐metal is at least 65 and that above 15 eV significant fragmentation of YO by the ionizing electrons to yield Y+ occurs. From the absolute effusion rates one derives the free energy of formation, ΔFf∘(YO,g)=−21 800–10.96 T, and the dissociation energy, 7.31±0.10 eV, for gaseous yttrium monoxide. A correlation of the dissociation energies and the molecular parameters of the monoxides of Group III transition metals indicates that the unexpected increase in bonding with increasing radii is accompanied by an increase in the electronic entropy of the metal atom. The correlation demonstrates the role ...

Enthalpy of Sublimation of Zinc and Cadmium; Correlation of ΔH°0 vs ΔS°; Comparison of Torsional and Knudsen Vapor Pressures

The vapor pressures of solid zinc and cadmium have been determined directly by measurements of the torsional recoil of a suspended effusion cell (p) and indirectly by measurement of mass effusion (π). The results with R in calories/mole·degree and p and π in atmospheres are as follows: For zinc (610°–690°K) the torsional recoil yields lnp = − (30.370 ± 0.070) × 103 (RT)−1 + (27.215 ± 0.107)R−1, at 645°K logp = − 4.3423 ± 0.0011; the mass effusion yields lnπ = − (30.379 ± 0.126) × 103 (RT)−1 + (27.087 ± 0.193)R−1, at 645°K log π = − 4.3733 ± 0.0016; for cadmium (525°–590°K) the torsional recoil yields lnp = − (26.361 ± 0.123) × 103(RT)−1 + (27.135 ± 0.219)R−1, at 555°K logp = − 4.4501 ± 0.0017; the mass effusion yields lnπ = − (26.172 ± 0.139) × 103(RT)−1 + (26.672 ± 0.247)R−1, at 555°K logπ = − 4.4768 ± 0.0019. In these equations the cited errors are standard deviations generated in least‐squares analyses. The measured pressures for zinc and cadmium are 1.075(± 0.01) and 1.063(± 0.01), respectively, times...

Heat and Entropy of Sublimation of Nickel Dichloride, Dibromide, and Di‐iodide; Dissociation Energies of Gaseous NiCl2 and NiBr2

The vapor pressures of solid anhydrous nickel dichloride, dibromide, and di‐iodide have been measured directly by measurement of the torsional recoil of a suspended effusion cell and indirectly by measurement of mass effusion. The results with R in calories/mole·degree and p and π in atmospheres are as follows: NiCl2(550°–608°C): RT lnp = − (53.59 ± 0.41) × 103 + (43.70 ± 0.48)T, at 855°K logp = − 4.1472 ± 0.0020; RT lnπ = − (52.76 ± 0.40) × 103 + (42.63 ± 0.46)T, at 855°K logπ = − 4.1670 ± 0.0019. NiBr2(519°–584°C): RT lnp = − (53.01 ± 0.76) × 103 + (45.11 ± 0.95)T, at 820.16°K logp = − 4.2595 ± 0.0036; RT lnπ = − (51.97 ± 0.27) × 103 + (43.73 ± 0.33)T, at 820.16°K logπ = − 4.2843 ± 0.0014. Nil2(462°–505°C): RT lnp = − (35.58 ± 0.36) × 103 + (32.60 ± 0.52)T; RT lnπ = − (37.39 ± 0.24) × 103 + (34.93 ± 0.34)T. For the chloride and the bromide, the measured pressures are 1.05(± 0.02) times the equivalent mass effusion (π) for a molecular weight corresponding to the monomeric dihalide. This deviation from un...

Molecular and Hydrodynamical Effusion of Mercury Vapor from Knudsen Cells

The unilateral flow of saturated mercury vapor through cylindrical channels of stainless steel and a thin‐edged orifice into a vacuum has been investigated at source pressures ranging from 10—6 to 1 atm. The results generally agree with the semitheoretical equation derived by Knudsen in a study of the bilateral flow of permanent gases under small pressure gradients, but significant differences exist. For channels with ratios of length to radius of about 60 to 100 and radii of about 0.02 cm, the agreement is within the experimental errors for pressures ranging from the lowest of 10—6 to about 5×10—4 atm. Above this latter value the rate of flow is less than that predicted by the equation, and at pressures near 1 atm the rate tends to approach that value which is expected for a situation in which the channel is filled with the saturated vapor. For the thin‐edged orifice the results display the molecular flow and a transition to hydrodynamic flow which is nearly isothermal. For an intermediate value of the r...

Spectroscopic and structural characterization of tetrabutylammonium trihalides: n-Bu4NI3, n-Bu4NI2Br, n-Bu4NIBr2, and n-Bu4NAuI2; Precursors to organic conducting salts

Abstract The tetrabutylammonium trihalides are used as precursors in the electrocrystallization of the organic superconductors β-(BEDT-TTF)2X where X = I3−, IBr2− and AuI2−and also in the synthesis of metallic but non-superconducting β-(BEDT-TTF)2I2Br. The infrared, Raman and photoelectron spectra and the X-ray crystal structures of n-Bu4N.Y, where X = I3−, I2Br−, IBr2− and AuI2− have been investigated to furnish information as to which geometrical, vibrational and electronic factors contribute to the electrical conduction properties of the aforementioned synmetals. Structural and vibrational data indicate that the I3−, IBr2−2 and AuI2− anions are essentially linear and symmetrical whereas the I2Br− salt contains linear but non-symmetrical I-I-Br− anions. The photoelectron, infrared and Raman spectra of this salt do not coincide with those of a mixture ( 50 50 ). In addition, the photoelectron spectra for I3d 5 2 reveal the presence of two charge states for the I atoms in the I2Br− anion. Structural data for n-Bu4NI2Br, which was found to be isostructural to the previously determined n-Bu4NI3, show that the I2Br− anions are disordered and form infinite chains in channels in the cation lattice. The structures of n-Bu4NIBr2 and n-Bu4NAuI2 contain isolated anions.

The evaporation behaviour of neptunium dioxide

Abstract The evaporation behaviour of neptunium dioxide in vacuo has been studied over the temperature range 1850–2475°K. The gaseous oxides NpO 2 and NpO were the only species observed and the temperature dependence of the major species NpO 2 was measured mass-spectrometrically. The total mass effusion rates were determined by collecting known fractions of effusate which were subsequently assayed by alpha counting of 237 Np. The effect on the partial pressures due to the variation of sample size and the fractional amount evaporated indicates that the solid dioxide becomes substoicheiometric and produces a bivariant system. The extent of substoicheiometry, although unknown, grossly affects the partial pressure of NpO(g) but has an insignificant influence on the partial pressure of NpO 2 (g). The experimental results are combined with known and estimated thermodynamic data to yield the standard free energy of formation of NpO 2 (g), ΔG f °(NpO 2 , g) = −114,000 + 3·5 T the dissociation energy of NpO 2 (g), 14·3 ± 0·3 eV, and an estimated value for the dissociation energy of NpO(g), 7·4 ± 0·3 eV.

Uranium Monosulfide. III. Thermochemistry, Partial Pressures, and Dissociation Energies of US and US2

A mass‐spectrometric study of the sublimation of uranium monosulfide has been performed over the temperature range 1825° to 2400°K. The data are combined with the previous measurements of absolute rate of effusion by means of a new method of calculation which effects an absolute pressure calibration of the spectrometer and allows a determination of the partial pressures of U, US, and US2 in the vapor, the enthalpies and entropies of sublimation to atoms and molecules, and the dissociation energies of US and US2. The partial pressures of U, US, and US2 at 2020°K are in the ratios 1/0.27/0.001. The data for the several sublimation processes are as follows:     Reaction                  logP (atm)ΔH2020∘ kcal/moleΔS2020∘ cal/mole·degUS(s)=US(g)logPUS=(7.606±0.091)−(31 030±190)/T142.0±0.934.8±0.4US(s)=U(g)+S(g)logPU=(7.323±0.081)−(29 600±170)/T270.9±0.1665.0±0.72US(s)=US2(g)+U(g)logPUS2=(6.36±0.26)−(33 430±580)/T288.4±3.762.6±1.2 The quoted uncertainties are standard deviations. The dissociation energies for ...