Index of content:
Volume 44, Issue 8, 15 April 1966
44(1966); http://dx.doi.org/10.1063/1.1727141View Description Hide Description
Thermal conductivities for argon in the dense gaseous state were determined at 6.2°, 20.7°, 25.0°, and 48.8°C for pressures up to 10 340 psia, using a coaxial cylindrical cell. These values were found to be in good agreement with thermal conductivities reported by others and when expressed as residual quantities, k—k *, unique relationships resulted with ρ R and the . These relationships were independent of temperature and pressure and included both the dense gaseous and liquid states.
The Enskog equation for the effect of pressure on thermal conductivity,,has been applied to the data of this study and of others for the dense gaseous and liquid regions, to obtain values of b. These values were found to be independent of pressure and to depend upon temperature as follows: . For these calculations, values were established from PVT data for argon. The experimental values obtained in this study were used to determine (k/ρ)min for each temperature, which were used in conjunction with the Enskog equation to produce thermal conductivities at elevated pressures. Values calculated with (k/ρ)min produced an average deviation of 1.2%, whereas the values resulting from gave an average deviation of 2.0%.
44(1966); http://dx.doi.org/10.1063/1.1727142View Description Hide Description
Measurements are reported of the nuclear spin—lattice relaxation timeT 1 in pressurized samples of liquid hydrogen. T 1 has been measured as a function of density, temperature, and orthohydrogen concentration in the temperature range 20.7° to 31.2°K. The data are compared with some theoretical calculations of Deutch, based on the Bloom—Oppenheim theory of nuclear spin—lattice relaxation. The density dependence of (T 1) ortho—para is found to be opposite to that of (T 1) ortho—ortho at constant temperature. This inverted density dependence is discussed and compared with an inverted ``temperature'' dependence reported by other workers.
44(1966); http://dx.doi.org/10.1063/1.1727143View Description Hide Description
The theory of nuclear spinrelaxation in gases and liquids developed by Bloom and Oppenheim is applied to the liquid‐hydrogen system. An explicit expression for T 1 in terms of correlation functions of the anisotropicintermolecular potential is obtained. Two terms contribute to T 1. The first term is independent of the ortho concentration and arises from the anisotropic potential that exists between an ortho molecule and a para molecule or the spherically symmetric part of another ortho molecule. It is suggested that three‐particle correlations must be explicitly considered if one is to understand the magnitude and the temperature and density dependence of this term. The second contribution is linear in the ortho concentration and arises from the anisotropic potential between the asymmetric part of two ortho molecules (quadrupole—quadrupole interaction). Theoretical calculation of this term agrees remarkably well with experiment. It is found that a dynamical model of the molecular motions (CAA) is more satisfactory than a diffusion model (DCAA) in the calculation of the quadrupole—quadrupole interaction effects.
44(1966); http://dx.doi.org/10.1063/1.1727144View Description Hide Description
Features appearing at 393, 1241, and 2847 cm−1 after photolysis of matrix‐isolated cyanogen azide with 2100–2800‐Å radiation are shown to exhibit parallel behavior. Isotopic data are consistent with the assignment of these three features as fundamentals of the free radical CNN, produced by the reaction of carbon atoms with molecular nitrogen. Ultraviolet absorptions at 4189 and 3964 Å can also be assigned to CNN. The force constants and thermodynamic properties of CNN have been derived. The carbon—nitrogen bond is found to have approximately triple‐bond character and the nitrogen—nitrogen bond approximately double‐bond character.
44(1966); http://dx.doi.org/10.1063/1.1727145View Description Hide Description
Viscosity and density data were obtained for several series of alkali aluminosilicate melts between 1200° and 1700°C with a counterbalanced sphere viscometer. Property comparisons are presented as functions of the SiO2 content, Na2O content, and constant Al/Na ratios at 1500° and 1700°C.
The viscosity and expansion information support the formation of three‐dimensional cristobalitelike liquids on the Al/Na=1.0 line with some of the aluminum (III) in the form of AlO6 octahedra for Al/Na>1.0 melts.
The molar volume models that coincide with experiment for Al/Na≤1.0 melts involve AlO4 tetrahedra and v̄ Na2O values that increase with increase of the Al2O3 content. The model that best agrees with experiment for melts with Al/Na>1.0 involves only some of the excess aluminum ions in octahedral coordination as well as a changing v̄ Na2O. Melt molar volume dependencies on composition can resemble those observed for similar glasses, which suggests structural similarities. The present liquid structure picture differs somewhat from previous concepts of alumina‐rich glass structures in this ternary system.
44(1966); http://dx.doi.org/10.1063/1.1727146View Description Hide Description
DMSO and TCNE form a strong 1:1 charge‐transfer complex (K 25°C=95.4) with an absorption band located at λ=3720 Å. The high enthalpy of complex formation (−11.3 kcal/mole) leads to an appreciably populated triplet state during complex formation. The EPR signal of the TCNE anion arises, reaches a maximum, and then follows second‐order decay kinetics. The initial intensity of the EPR signal is proportional to the original TCNE concentration in DMSO. A molecular mechanism for the equilibrium reaction between TCNE and DMSO is proposed.
44(1966); http://dx.doi.org/10.1063/1.1727147View Description Hide Description
The temperature dependence of the vapor pressure of europium in equilibrium with solid europium dicarbide (EuC1.87±0.07) and graphite has been measured over the temperature range 1130° to 1600°K by both time‐of‐flight mass spectrometric and target collection techniques. From the vapor‐pressure equation, the enthalpy of disproportionation of europium dicarbide is calculated to be 51.06±1.25 kcal/gfw by a second‐law treatment of the data, and 51.24±2.0 kcal/gfw by the third‐law method. The entropy of dissociation is calculated to be 18.43±1.70 eu/gfw. Combination of these data with the reported enthalpy and entropy of vaporization of elemental europium gives −9.17±1.15 kcal/gfw as the standard heat of formation and −7.47±1.87 kcal/gfw as the standard free energy of formation of europium dicarbide.
44(1966); http://dx.doi.org/10.1063/1.1727148View Description Hide Description
Reactions of the OH radical with OH, H2, and CO have been studied at room temperature in a fast flow system at pressures of the order of 1 mm. The very fast reaction between H atoms and NO2 was used as the source of OH. Electron spin resonance techniques were employed to examine the decay of OH concentration along the flow tube, using NO gas as the calibration standard. Rate constants at 300°K were found to be, in cubic centimeters per mole·second units
Combination of the last two of these with published results at higher temperatures leads toor in simple Arrhenius form
44(1966); http://dx.doi.org/10.1063/1.1727149View Description Hide Description
The electron spin resonance spectrum of the perinaphthenyl radical has been studied in the isotropic and nematic phases of p‐azoxyanisole. The gtensor and hyperfine splittingtensors for the two proton couplings and three of the four carbon−13 couplings have been determined, and were found to agree in most cases with theoretical estimates. Ordering of the radical was also deduced as a function of temperature in the liquid‐crystal range, and corresponded to the ordering of the solvent molecules.
A general expression for the effective spin Hamiltonian of a radical in a liquid crystal is derived. Zeemananisotropy and dipolar electron—nuclear couplings are shown to result in g shifts and changes in the hyperfine splitting coefficients.
44(1966); http://dx.doi.org/10.1063/1.1727150View Description Hide Description
The yield of solvent‐trapped electrons in γ‐irradiated 3‐methylpentane at −196° was 0.75 per 100 eV when measured within a few seconds, and diminished to ∼0.6 after 3 min. The quantum yield for bleaching at 950 mμ decreased from 0.8 toward zero with progressive bleaching. Addition of 0.05% biphenyl maintained the quantum yield at >0.8 until more than 90% of the solvent trapped electrons had bleached. The initial quantum yield at λ>1.7μ was ∼0.01, both with and without added biphenyl. There is qualitative correlation between photobleaching and the rate of spontaneous decay.
44(1966); http://dx.doi.org/10.1063/1.1727151View Description Hide Description
A clean (110) tungstensurface can adsorb CO molecules in two different ways. Those striking bare surface have high sticking probability and are held firmly with possible rearrangement of the surface‐metal atoms. Molecules striking an already covered surface have a somewhat lower sticking probability and are held more weakly. Temperatures producing rapid desorption of the two components are 450° and 1100°K. The maximum coverage in the first layer is not pressure dependent. In the second layer the maximum coverage is about 0.8 of the first‐layer coverage at 10−7 torr but decreases slightly at lower CO pressures. The structure of the first layer, as found by LEED observations, is very disorganized unless the crystal is heated; but a well‐ordered structure is produced by heating at 925°K and poorer order by heating at lower temperatures. The ordered surface mesh is C(9×5). The detailed structure has not been determined. The intensities of various diffraction beams from a clean surface change in very complicated ways when the primary beam energy is altered; the variation with energy is much simpler when CO is adsorbed on the surface. A suggested distortion of the clean surface that accounts for these facts is presented.
44(1966); http://dx.doi.org/10.1063/1.1727152View Description Hide Description
The transients of volume‐controlled doubly injected currents and of the accompanying recombination radiation were measured on anthracene crystals. By this method, which allows the trap‐free case to be approximated, the carrier recombination rate constant K was determined in a more reliable way than is possible with steady‐state currents. The result, K=(1.05±0.5)×10−6 cm3 sec−1, agrees well with the theoretical value predicted by a model in which the rate is a function of carrier mobility. The recombination fluorescence was found to consist of two components differing by their rise times. The fast component, I fast, is due to singlet excitonsgenerated directly by carrier recombination. The slow component, I slow, is proof that carrier recombination produces also triplet excitons (which can recombine to give singlets producing fluorescence). The ratio I slow/I fast=0.65±0.1 indicates that two recombining triplet excitons do not always produce a singlet exciton but may also form an excited triplet exciton. In addition, the light transient measurements permitted the determination of the total rate constant, γtotal, of triplet—triplet recombination in a novel way. The result is γtotal=(4–8)×10−12 cm3 sec−1.
44(1966); http://dx.doi.org/10.1063/1.1727153View Description Hide Description
The absorption and fluorescence spectra of Pr3+ in LaCl3 have been examined for molar concentrations of 0.26%, 2%, 15%, 50%, 85%, and 100%, and have been used to determine the effect of concentration on the energy levels and transitions of the ion. A model is advanced to explain the concentration broadening of spectral lines in crystals as due to heterogeneity of the lattice and resonance interaction between the spectroscopically active ions. Oscillator strengths were measured for the dilute crystal and the ratio of the strength of the ion‐pair absorption3 P 0+3 F 2(μ=2) to that of 3 P 0, in PrCl3, was found to be 1.3×10−5.
44(1966); http://dx.doi.org/10.1063/1.1727154View Description Hide Description
Vitreous films of zinc 9‐anthroate have p‐type dark conductivity and photoconductivity and a high density of traps. The photoconductivityspectrum shows a single peak near the long‐wavelength edge of the first absorption band. An explanation for this peak is that light of wavelength longer than that of the peak is weakly absorbed, while light of shorter wavelength penetrates only a short distance, producing high concentrations of charge carriers, which rapidly recombine.
44(1966); http://dx.doi.org/10.1063/1.1727155View Description Hide Description
A study of the clean and oxygen‐covered molybdenum (110) surface has been carried out using low‐energy electron‐diffraction techniques. The clean surface is found to be the same as an ideal (110) plane in the bulk. Oxygen structures corresponding to ¼, ½, and ¾ monolayer have been found. These structures are very similar to those found for the tungsten (110) surface. Experiments on nitrogen and hydrogen adsorption are inconclusive due to interference from other residual gases (primarily carbon monoxide).
44(1966); http://dx.doi.org/10.1063/1.1727156View Description Hide Description
The relaxation time of the fluorine nuclei in benzotrifluoride has been measured and is found to be an only slightly varying function of temperature, ranging from 3.2 sec at −20°C to 2.4 sec at +50°C. The contributions to the relaxation time from the dipole—dipole and spin—rotation interactions have been separately calculated, and the effective spin—rotation coupling constant is calculated to be 25±2 kc/sec. This coupling constant has been used to calculate the paramagnetic contribution to the chemical shift of the fluorine in C7H5F3 relative to F2, and yields the value, 453 ppm, which is within 10% of the observed value or 493.3 ppm for the chemical shift.
44(1966); http://dx.doi.org/10.1063/1.1727157View Description Hide Description
Depending upon the circumstances, the phenomena which accompany or are the consequences of two‐photon absorption may be quite varied. The effects which have been reported to date are luminescence, internal and external photoelectric generation, and initiation of chemical reactions. In this paper, we point out that generation of soundwaves may also be expected on a theoretical basis, and we present experimental results which we believe may have demonstrated this effect in liquids consisting of solutions of molecules such as benzanthracene and benzpyrene.
44(1966); http://dx.doi.org/10.1063/1.1727158View Description Hide Description
Absorption and photoionization coefficients of CO2 have been measured in the regions of strong band and continuous absorption in the spectral range between 1000 and 600 Å. The total continuum underlying the band structure has been estimated as well as that fraction due to ionization and dissociation. A strong fluorescent edge was observed at 715.7 Å and was found to contain vibrational structure.
44(1966); http://dx.doi.org/10.1063/1.1727159View Description Hide Description
An expression for the energy of interaction between two molecules has been obtained by solving the secular equation using a double‐iteration procedure based on the exact wavefunctions of the isolated molecules. This expression exhibits the intermolecular interaction energy explicitly and its leading terms agree with those recently obtained by Murrell et al. and Salem within the limits specified by these authors.
44(1966); http://dx.doi.org/10.1063/1.1727160View Description Hide Description
The electrical conduction of aqueous 0.001, 0.01, and 0.1M MgSO4 solutions has been measured over the range −2° to +12°C. The activation energy of electrical conduction of aqueous MgSO4 solutions, unlike those of solutions of ``normal'' strong 1:1 electrolytes, does not exhibit a maximum near the temperature of maximum density. The local water structure near MgSO4 is so strong and extensive that structural changes in the more remote bulk water have little effect on transport processes involving MgSO4. The mechanism of this process apparently resembles that of viscous flow in water rather than ``normal'' ionic electrical conduction.