Index of content:
Volume 44, Issue 10, 15 May 1966
44(1966); http://dx.doi.org/10.1063/1.1726510View Description Hide Description
NMR pulse techniques have been used to study the influence of hydrostatic pressure on self‐diffusion in four organic solids composed of nearly spherical molecules: cyclohexane, 2,2‐dichloropropane, t‐butyl chloride, and t‐butyl bromide. The self‐diffusion was studied from the pressure and temperature dependence of T 2, the spin—spin relaxation time, at pressures between 1 and 680 atm, and at temperatures within 10–50 deg of the melting point. The measured activation volumes were 8%—15% of the molar volumes. Comparable ratios have been previously observed for rotational motion in similar solids. The activation enthalpies for self‐diffusion were 5–6 kcal/mole, somewhat exceeding the values for rotational motion. Comparisons are made with the latent volumes and enthalpies of fusion.
44(1966); http://dx.doi.org/10.1063/1.1726511View Description Hide Description
Using a torquemagnetometer, experimental results are reported on some new magnetic properties in high‐purity, optical‐quality single crystals of lithium fluoride, potassium chloride, and sodium chloride. Since the torque observations are not produced by the gross diamagnetism of these salts, the magnetic centers may be along dislocations because the magnetic susceptibility is observed to possess uniaxial anisotropy. Soft x irradiation increased the observed magnetization. In addition, there is a cooperative interaction among the magnetic centers which gives a remanent magnetization. The temperature dependence of the remanent magnetization is similar to the Bloch spin‐wave concept of ferromagnetism. These new magnetic properties are an order of magnitude smaller when measured in crystals of magnesium fluoride and of calcium fluoride.
44(1966); http://dx.doi.org/10.1063/1.1726512View Description Hide Description
Calculations of the first four 1Σ g + and first three 3Σ g + states of H2 are carried out in lowest order of the partial wave theory of H2. Solutions are obtained using Hylleraas‐type variational functions for the two electrons containing up to 50 terms. Comparison of the singlet potential‐energy curves with precision curves, where available, reveals a comparable accuracy to what was obtained in the case of H2 + for the lowest state but not for higher states. The particular relevance of these wavefunctions as target wavefunctions in calculations of electron—molecule scattering is discussed.
44(1966); http://dx.doi.org/10.1063/1.1726513View Description Hide Description
The thermal dissociation of molecular fluorine in an inert gas was investigated over the temperature range 1650°—2700°K in a shock tube coupled to a time‐of‐flight mass spectrometer. Rate constants were determined from both fluorine molecule and atom analysis in mixtures containing 1% F2 or less. The results are compared with the results for other diatomic molecules and the variations discussed.
A simple correlation between the orifice flow parameters and the experimental spectra is presented along with some information concerning the rather elusive boundary layer.
44(1966); http://dx.doi.org/10.1063/1.1726514View Description Hide Description
The xenon‐sensitized radiolysis of propane has been investigated in the presence and absence of small amounts of ion and free radical interceptors. From an analysis of mixtures of deuterated propanes and a knowledge of radical disproportionation yields in the scavenged and unscavenged systems it is possible to construct a complete quantitative kinetic analysis for the decomposition. Ion titration methods demonstrate that the neutralization of C3H7 + ions occurs heterogeneously in the system investigated and leads quantitatively to the production of equivalent yields of isopropyl radicals and hydrogen atoms.
44(1966); http://dx.doi.org/10.1063/1.1726515View Description Hide Description
The chief effect of ionizing radiation on polytetrafluoroethylene oxide (PTFEO) is to induce main‐chain scission. The ESR spectrum of the irradiated polymer in vacuum consists of two components. The stable spectrum is attributed to the –CF2–CF2–O. and –O–ĊF–CF2–O– radicals. The former radical decays slowly at room temperature, the latter is unchanged even after several weeks. The unstable spectrum disappears in a few hours and its structure is uncertain. Tentatively this spectrum is assigned to the –O–CF2–CF2 . radical. Admission of air to the irradiated polymer gives rise to a spectrum formed of a symmetric singlet assigned to –CF2CF2–OO. radical and an asymmetric signal toA G fracture=1.8 has been calculated from viscosity data.
44(1966); http://dx.doi.org/10.1063/1.1726516View Description Hide Description
The attenuation coefficient α of longitudinal acoustic waves propagating along the  direction in ammonium chloride has been reinvestigated as a function of frequency from 10 to 60 Mc/sec and of temperature from 215° to 300°K. Special emphasis was given to 10‐Mc/sec data at temperatures very close to the order—disorder transition, and hysteresis was observed. These attenuation data are consistent with the behavior expected from a compressible Ising model which predicts a mechanical instability in the immediate vicinity of the transition temperature.
44(1966); http://dx.doi.org/10.1063/1.1726517View Description Hide Description
The fundamental frequency assignment of thionyl fluoride has been made from Raman spectra of the liquid at −100°C and the gas at 2.5 atm and the infrared spectrum of the gas. The sample used has a purity of greater than 99.9 mole %. The fundamental frequency assignment with the following frequency values taken from the infrared spectrum is ν1(a′), 1329.9, 1339.3 cm−1 (Fermi resonance doublet); ν2(a′), 808.2 cm−1; ν3(a′), 530.4 cm−1; ν4(a′), 377.8 cm−1; ν5(a′), 747.0 cm−1; ν6(a″), 392.5 cm−1.
The symmetric and asymmetric SF2 bending modes, ν4 and ν6, have been definitely identified in all the spectra and their symmetry characterized by polarization measurements from the Raman spectrum of the liquid.
44(1966); http://dx.doi.org/10.1063/1.1726518View Description Hide Description
The existence of a p—n junction is shown to be able to account for non‐Hecht pulse‐height‐vs‐voltage curves in pulsed photoconductivity measurements. No changes in the pulse‐height‐vs‐voltage curves were observed in crystalline anthracene, however, when capacitive feedback was used to eliminate the effect of such a junction.
Effects of Electron Correlation in X‐Ray and Electron Diffraction. III. Experimental Electron—Electron Distribution Functions44(1966); http://dx.doi.org/10.1063/1.1726519View Description Hide Description
Radial distribution functions of electrons with respect to the other electrons in neon and argon atoms are derived from Laurila's experimental x‐ray intensities. The resulting distribution functions are used to calculate experimental electron—electron potential‐energy values. In qualitative features the distributions compare favorably with those calculated from existing wavefunctions. Uncertainties in the distribution functions due to the scatter of experimental data points and to the restricted angular range of the data were large enough to obscure effects of electron correlation.
44(1966); http://dx.doi.org/10.1063/1.1726520View Description Hide Description
Oxygen gas was observed by means of a mass spectrometer to be evolved from calcium‐doped ceramiccerium oxide when direct current was passed through it at 450°C. The applied voltage necessary to cause the electrolysis was about 100 V across a sample 4 mm long containing 0.86 at. % calcium. When voltages of 1.0 V or less were applied to ceramic and single‐crystal samples there were pronounced transients and nonlinear potential distributions. These latter effects appear to be consistent with a picture of oxygen ions migrating to an electrode where they are at least partially blocked.
44(1966); http://dx.doi.org/10.1063/1.1726521View Description Hide Description
The melting curve of iodine, which has been determined by differential thermal analysis, monotonically increases from about 114°C at zero pressure to about 590°C near 30 kbar. The extrapolated zero‐pressure slope for the melting curve is consistent with the value of 27.2 deg/kbar, as calculated from zero‐pressure data for the volume and entropy changes, and with the 27.8‐deg/kbar value from the unpublished data of Babb; near 30 kbar, the slope is about 11 deg/kbar. To a good approximation, the melting characteristics of the isostructural elements—iodine, bromine, and chlorine— should be quite similar, and the data for these other halogens are examined in an effort to anticipate their behavior at high pressure.
44(1966); http://dx.doi.org/10.1063/1.1726522View Description Hide Description
The definition of an alternant system is given in terms of commutation and anticommutation relations of the Hamiltonian with certain operators. Necessary and sufficient conditions that the Hamiltonian fulfill these relationships are formulated. Different known cases of alternant systems are derived from the definition. Pairing properties are shown to follow as consequences of the definition, and they are summarized in simple general equations for matrix elements of an arbitrary operator.
44(1966); http://dx.doi.org/10.1063/1.1726523View Description Hide Description
The intensity of back‐diffracted low‐energy electrons (15–350 eV) from the clean (100), (111), and (110) surfaces of platinumsingle crystals was measured. From the temperature dependence of the (00) reflection in the range of 25°—700°C, the Debye—Waller factor and the root‐mean‐square displacements of surface atoms perpendicular to the surface planes were determined. The measured root‐mean‐square displacement 〈u z 2〉½ was found to be a sensitive function of electron energy. The properties of the surface planes were determined from the intensity data taken at the lowest electron energy. Using the Debye model in the high‐temperature approximation, the Debye temperatures and the frequencies of lattice vibration were calculated. The root‐mean‐square displacement of surfaceplatinum atoms perpendicular to the surface plane is about twice as great as that in the bulk. This effect gives rise to surface Debye temperatures which are much smaller (107°—118°K) than the bulk value (234°K).
44(1966); http://dx.doi.org/10.1063/1.1726524View Description Hide Description
Glycerol—water mixtures containing up to 68 mole % water were subjected to ultrasonic shear and longitudinal measurements over the temperature range +50° to −120°C. The low‐frequency absorption coefficient and the velocity of sound were measured at 25°C for various glycerol—water mixtures from pure glycerol to pure water. The results demonstrate the existence of low‐ and high‐frequency limiting compressional moduli and a high‐frequency limiting shear modulus. The relaxational moduli were found to be linear with temperature for each concentration, and also were linearly dependent on water content.
The width of the distribution of relaxation times was found to be independent of water content up to 68 mole %. This result fails to support Frohlich's model for the origin of the distribution of relaxation times.
Estimated values of the relaxation parameters of water were obtained from the data. Those which were obtained by extrapolation appear to be reasonable when compared with theoretically obtained values.
44(1966); http://dx.doi.org/10.1063/1.1726525View Description Hide Description
The 4 A 2ground state of tetrahedrally coordinated divalent cobalt ions in Cs3CoCl5 and Cs3CoBr5 is investigated with magnetic‐susceptibility measurements and paramagneticresonance in pulsed magnetic fields up to 90 kOe at frequencies in the 70‐ and 120‐Gc/sec bands. The first excited state (4 T 2) which lies ∼3000 cm−1 above the ground state is studied optically on Cs3Zn0.9Co0.1Cl5. The sign of the splitting of the 4 T 2 state is opposite to that expected from the observed negative zero‐field splitting of the ground state.
44(1966); http://dx.doi.org/10.1063/1.1726526View Description Hide Description
Integrated intensities of the 152–175‐cm−1 intermolecular Raman bands from water and ∼2M aqueous solutions of urea and sucrose were obtained. The intensity data and the stoichiometric water molarities of the solutions were then employed in conjunction with an operational definition to obtain information related to ``structure‐breaking'' and ``structure‐making'' effects. Urea and sucrose were thus found to produce effects on the water structure in general agreement with the work of Klotz and of Frank.
44(1966); http://dx.doi.org/10.1063/1.1726527View Description Hide Description
The polarization of the π, π*phosphorescence emission of quinoxaline (1,4‐diazanaphthalene) dissolved in EPA rigid glass as well as in durene host crystal has been measured and the two compared. The polarization characteristics of the different vibronic bands in the two hosts indicate that the emission originates from at least two mechanisms—a first‐order mechanism that gives rise to Subspectrum I with the 0, 0 band as its origin, and a second‐order, spin—orbit—vibronic mechanism that gives rise to Subspectrum II. When the host is changed from EPA to durene, the polarization of Subspectrum I in the quinoxaline framework seems to change from out of plane to long axis. Subspectrum II seems to be less sensitive to host‐crystal effects than Subspectrum I. The similarity of these results to those obtained previously for naphthalene‐d 8 (Chaudhuri and El‐Sayed) might indicate that the lone pair on the nitrogens in quinoxaline plays no specific role in explaining this phenomenon. This conclusion suggests that the most probable configuration for quinoxaline in durene is that in which the lone pairs on the nitrogen atoms of quinoxaline are far away from the methyl groups of durene. The observed durene host‐crystal effects on the emission of quinoxaline can be explained in a similar manner to those given for naphthalene. It is proposed that the quinoxaline molecule in durene crystal is slightly nonplanar in its triplet state due to repulsive forces of the methyl hydrogens of durene and the hydrogen atoms of the quinoxaline molecule. The nonplanarity results in an enhancement of the spin—orbit interaction between singlet and triplet π, π* states and thus introduces long‐axis polarization. Mixing between quinoxaline triplet state and durene‐crystal states is an alternative mechanism and is briefly mentioned.
44(1966); http://dx.doi.org/10.1063/1.1726528View Description Hide Description
C3H6–C3D6–O2 mixtures have been irradiated at 1236 Å (10 eV) in the presence and absence of an applied electrical field with the purpose of obtaining information about the ion—molecule reaction mechanism. On the basis of a number of observations, it was concluded that the product, propane, can be ascribed to the reaction C3m H6m ++C3H6→C3m H6m−2 ++C3H8 (m≥2). When alkanes (RH2) whose ionization energy is larger than 10 eV are added to C3D6—O2 mixtures, the following H2 −‐transfer reaction occurs: C3D6 ++RH2→CD3CDHCD2H+R+ . Relative rates of the reaction of C3D6 + with various alkanes have been determined and compare favorably with values obtained in a recent radiolytic study in which cyclopentane‐d 10 was used as a source of C3D6 + ions.
The optimum experimental conditions, under which meaningful saturation ion currents can be obtained in the photoionization apparatus, are discribed. On the basis of measurements of the saturation ion current in NO and propylene at 1236 Å, values of 0.197 and 0.208 were obtained for the photoionization efficiencies of C3H6 and C3D6, respectively. The latter measurements made it possible to express the products in the number of molecules formed per ion pair as well as in the number of molecules formed per quantum absorbed.
44(1966); http://dx.doi.org/10.1063/1.1726529View Description Hide Description
Absolute measurements were made of the intensity of emission from atomic oxygen (5577 Å), molecular oxygen (the Herzberg bands below 4000 Å, the atmospheric band at 7618 Å), nitric oxide (the β bands below 4000 Å), and molecular nitrogen (the first positive bands from 5000 Å to 6000 Å) when excited in a low‐pressure gas atmosphere containing atomic nitrogen and/or oxygen in absolutely measured quantities. The relationship between light emission and atomic concentration, pressure, gas mixture, and quenching gas concentration was obtained. With these data as bases, excitation and de‐excitation processes are discussed and rate coefficients of several elementary processes deduced. These have been applied to nightglow phenomena of the earth's upper atmosphere.