Pressure broadening and shift of argon emission lines

Resonance and van der Waals broadening coefficients, as well as width to shift ratios, have been obtained by scanning argon emission lines produced in a high-pressure (～ 1 atm) glow discharge at a temperature of 1130°K. The resonance broadening coefficients yield absolute oscillator strengths of 0·283 ± 0·024 and 0·076 ± 0·008 for the two resonance lines at 1048 Å and 1067 Å. These oscillator strengths are in good agreement with previous measurements. The importance of higher-order terms in the van der Waals potential expansion is demonstrated by the measured coefficients.     

Intramolecular Force Fields and Vibrational Amplitudes of Disulfur Monoxide Isotopes

The force constants of S₂O have been calculated smploying GVFF and UBFF models. The reliability of the set of force constants have been examined. The mean amplitudes of vibration have also been evaluated at three temperatures, viz., 0°K, 298·15°K and 500°K. The results have been briefly discussed. The mean amplitude values will be helpful in interpretation of the electron diffraction data whenever available.     

Leed measurements of the surface debye temperature for the (110) nickel face

Measurements of the surface Debye temperature for the (110) nickel face were performed in such a manner that difficulties in the interpretation known from the literature seem to have been avoided. A specular beam could reach a fluorescent screen for incidence angles 30° < β < 70°. A strong (00) beam was observed for (β ≈ 60° and electron energy E = 100–110 eV. For this beam, the dependence of its intensity on the sample temperature was measured and the effective Debye temperature was calculated to be equal to not more than 216 ± 10 K. Owing to the large β, the penetration depth of electrons should be equal to about 1.2 Å and only the first layer of atoms is responsible for diffraction in this case. Besides, it is shown that single scattering processes are dominant in our experimental conditions. So, the effective Debye temperature measured should be very close to the surface Debye temperature.     

The geometrical and vibrational properties of the Rh(111) surface

Low-energy electron diffraction (LEED) data have been used to characterize the clean Rh(111) surface. The surface geometry, the degree of surface relaxation, and the Debye temperature have been determined. In the Debye temperature measurement, specular LEED beam intensities were monitored as a function of temperature over a range of electron energies from approximately 30 to 1000 eV. It was found that the bulk Debye temperature is 380 ± 23 K, and the normal component of the Debye temperature at the lowest electron energy used is 197 ± 12 K. The Rh(111) surface relaxation has been determined both by a convolution-transform analysis and by dynamical calculations. Within experimental error, neither expansion nor contraction of the topmost layer has been detected. The results of the convolution-transform analysis of specular beams at two angles of incidence and of a nonspecular beam at normal incidence suggest an expansion of the topmost layer of 3 ± 5% of the bulk layer spacing. In agreement with this, comparisons between the results of the dynamical calculation and experimental data for five nonspecular beams at normal incidence suggest that the surface layer relaxes by 0 ± 5%. In addition, the dynamical calculations indicate that the topmost layer maintains an fcc structure.     

Structural studies of tetrachloride liquids

The differential cross-sections for neutron scattering from liquid carbon tetrachloride have been measured with the TSS instrument at the Harwell Electron Linac. Data were taken at seven different scattering angles for a wavelength range of 0·2–3·5 Å. The observed diffraction patterns at high momentum transfer (> 8–30 Å^-1) have been analysed in terms of the molecular form factor f ₁(Q). It was found that the oscillation amplitudes could be satisfactorily described only by introducing an energy-dependent term into the Debye-Waller factors of the form factor. The f ₁(Q) data were fitted with a four-parameter function for measurements at scattering angles of 150°, 90° and 58°. The carbon-chlorine bond length parameter was accurately defined in all cases and had a mean value of 1·766 ± 0·002 Å. The inclusion of an anharmonicity constant in the form factor gave an improved χ²-fit to the data with an increased value of 1·770 ± 0·002 Å for the bond length. The results are in excellent agreement with other measurements and show the importance of pulsed neutron techniques for molecular structure studies of disordered materials.     

Absence of premelting phenomena in pure perfect gallium crystals revealed by Debye-waller-factor measurements using anomalous diffraction of X-rays

Premelting phenomena have been searched for in pure, perfect gallium crystals by using anomalous X-ray transmission. The temperature dependence of the integrated intensity under the Bragg peak does not reveal any deviations from its normal behaviour, i.e. an essentially linear increase of the mean square vibrational amplitude of the lattice atoms as a function of temperature between 10 °C and a temperature at least 10^?4 °C close to the melting temperatureT _m =29.75 °C. The temperature dependence of the integrated intensity of the 020-reflection can be described by a Debye temperatureΘ ₍₀₂₀₎=189±6 K. Premelting effects could not be detected.     

One-centre matrix elements of the spin-other orbit operator in linear molecules: diagonal terms

The quasi-elastic scattering of cold neutrons from liquid and solid C₆H₆ and C₆D₆ has been measured at temperatures between 260 K and 325 K for incident wavelengths between 4·07 Å and 7·05 Å and for angles of scatter between 20° and 90° by means of a chopper time-of-flight apparatus. From the results, the total quasi-elastic intensity and the width of the corresponding broadening, presumed Lorentzian, were extracted. The broadening of the incoherent component in the scattering is discussed in terms of various models designed to combine the effects of centre of mass and jump rotational diffusion. All the models could be fitted to the results, using a root-mean-square jump length approximately equal to the nearest H-H distance. Using the ‘effective mass approximation’ the model can be extended to cover the coherent contributions to the scattering. When this is done, it is found that the fit is rather better if the rotational jumps are assumed not to contribute to the coherent broadening. The mean interval between jumps at 293 K was found to be 2·2 ± 0·5 × 10^-12 s with an activation energy of 2·1 ± 0·6 kcal/mole, in good agreement with 1·4 × 10^-12 s and 1·8 kcal/mole obtained by N.M.R. techniques.     

The structure of the water molecule in liquid water

The slow neutron scattering measurements of Walford, Clarke and Dore for liquid heavy water at 21°C for incident neutron wavelengths of 0·694 Å and 0·347 Å [7] have been reinterpreted using a sophisticated correction for recoil and detector effects [10] for the molecular contribution to the scattering cross-section. For momentum transfer greater than 6 Å^-1 the liquid structure contribution is negligible and a very good agreement between theory and experiment is obtained. It is concluded that the intramolecular oxygen nucleus-deuteron distance is 0·98₃±0·00₈ Å, and that the deuteron-deuteron distance is 1·55±0·02 Å. This molecular structure is nearer to that of the molecule in the vapour than that in ice I for the conventional interpretation for ice I. It is concluded that there is an environmental effect on the molecular internuclear distances at most of order 0·01 Å for the molecule in the orthobaric liquid near the triple point.     

Van der Waals broadening of argon absorption lines

Van der Waals broadening coefficients for Ar absorption lines have been measured using the resonant Faraday effect. These coefficients have the values of 2·9 ± 0·8, 2·4 ± 0·3, 1·9 ± 0·2 (in units of 10^?20 cm^?1 ?cm^?3) for the lines 6965 Å, 7067 Å, 7635 Å and 8115 Å, respectively, respectively. The measured coefficients are in reasonable agreement with measurements carried out on Ar emission lines and with theoretical calculations.     

A first-principles study on the structural and elastic properties and the equation of state of wurtzite-type cadmium selenide under pressure

A first-principles investigation on the crystal structural and elastic properties and the equation of state of wurtzite-type cadmium selenide (w-CdSe) has been conducted using the plane-wave pseudo-potential density functional theory and the quasi-harmonic Debye model. The elastic constants, the aggregate elastic moduli, the elastic anisotropy, and Poisson's ratio under pressure have been investigated. Our calculated equilibrium lattice constants, the elastic constants, and the aggregate elastic moduli at zero pressure are in good agreement with the experimental data and other theoretical results. The variations in the compressional and shear elastic wave velocities with pressure at zero temperature up to pressure 2.7 GPa have been studied; the computed Debye temperature at zero pressure and zero temperature is in reasonable agreement with the result of Bonello et al., In addition, the equation of state of w-CdSe in the pressure range of 0–2.7 GPa and up to a temperature of 900 K has also been obtained.     

Einfluß adsorbierter Gase auf Supraleitung und elektrische Leitfähigkeit dünner Thalliumschichten

Some effects of adsorbed gases on superconductivity and normal electrical conductivity of thallium films have been investigated. These films were 50 to 700 Å thick and were produced by condensation of thallium vapor on a crystalline quartz, plate at about 100 °K. At 3 °K adsorbed oxygen lowers the transition temperature and slightly increases the residual resistance. Heating of the film results in a steep increase of resistivity at about 15 °K and shifts the transition temperature to a considerably higher value. The changes in electrical conductivity and transition temperature increase with decreasing film thickness. With the thinnest films, the resistivity increases up to 50 per cent. The maximum shift of the transition temperature is 0·3 degrees. From the resistivity behavior, it can be inferred that the adsorbed oxygen molecules accept conduction electrons at 15 °K, thus changing the kind of their bond. This shows up in a decrease of the effective film thickness by 5 to 10 Å. Further, results of adsorption experiments with hydrogen, nitrogen and argon are reported. These results depend to a great extent on the purity of the gases.     

The exciton absorption in deformed germanium

Absorption spectra at 77° K near the direct (κ = 0) exciton transition are reported for deformed and undeformed single-crystal films of n-type Ge oriented on (111); Elliott's theory is applied. The optical width of the forbidden band for this transition is found as E_{g 0} = (0.8821 ±±0.0002) eV, while the exciton binding energy is found as E_ex(0) = = (0.0016±0.0003) eV for undeformed Ge at 77 ° K. The mean temperature coefficient of E_g for κ = 0 in the range 77 °–297 ° K is (dE_g/ /dT)_p =?3.50 · 10^?4 eV/deg. The effects of thermoelastic deformation on the exciton spectrum give (dE_g/dT)_d = (?1.5±0.1) · 10^?4 eV/deg. The half-width σ ≈ 5 · 10^?4 eV of the exciton peak gives the exciton lifetime as gt ≥ 10^?12 sec.     

Low temperature thermal properties of PbI2

The heat capacity and thermal conductivity of a large (56.5 g) crystal of PbI₂ have been measured in the temperature region 0.5 < T < 3.9°K. Analysis of the heat capacity data yields a value of the limiting apparent Debye characteristic temperature θ₀^c = 99.4 (±0.3)°K, which corresponds to an average lattice wave velocity of 1.151 (±0.005) × 10⁵ cm sec^?1. It is consistent with a wave velocity estimated from neutron scattering experiments, but not with one determined from Brillouin spectra. The heat capacity data also show that dispersion of the low frequency waves is not unusual, as might have been expected for a layer-type crystal. The apparent thermal conduction is found to be surprisingly small in the crystal.     

Das Quadrupolmoment des 8,42 keV-Niveaus von Tm169

The hyperfine interaction of the 8·42 kev level of Tm¹⁶⁹ was investigated using the Mössbauereffect in Tm-ethylsulfate. The hyperfine-splitting is of pure quadrupoletype; its temperature dependance between 6°K and 250°K was measured. The spectroscopic quadrupolemoment of the 8·42 kev level was determined asQ=?(1·1±0·1) barn, leading to an intrinsic quadrupolmoment ofQ ₀=+(5·5±0·5) barn.     

Hyperfine fields in erbium metal

The hyperfine Splitting of the 80.6-keVγ transition in Er¹⁶⁶ has been measured in erbium metal between 4.2 °K and 40 °K using the Mössbauer effect. There is evidence for a unique magnetic field and electric fieldgradient at all nuclei in erbium metal. The magnetic field decreases from (7.55±0.20)·10⁶ Oe at 4.2 °K to (6.10±0.40)·10⁶ Oe at 40 °K. Extrapolation to 0 °K yieldsH (0 °K)=(7.60±0.20)·10⁶ Oe. The quadrupole interaction energy for the 80.6-keV state iseQ V _Z′Z′/4=(0.95±0.20)·10^?6 eV at 4.2 °K. These results are discussed and compared with other measurements.     

Molecular motion in supercooled glycerol

Quasi-elastic Rayleigh scattering of 14·4 keV photons has been measured on supercooled liquid glycerol at -30°C and 0°C by employing the Mössbauer effect. Total scattered intensity, quasi-elastically scattered intensity I _q and energy width of I _q(k, ω) have been determined for k=0·6 to 4·2 Å^-1. The molecular motion is modelled as: random-walk diffusional motions for the centre-of-mass translation and for the orientation of independent rigid molecules, plus fast-bounded translational jitter (vibration). The model parameters are evaluated. The temperature dependence of the translational diffusion constant corresponds to an activation energy of 12 kcal/mol. Comparison is made especially with N.M.R. results for rotational motion. The effect of orientational jitter (libration) is considered and its possible influence on nuclear magnetic relaxation is pointed out.     

Electronic polarisabilities of ions in alkali halide crystals

Tessman, Kahn and Shockley calculated the electronic polarisabilities of ions in alkali halide crystals using the long wavelength limiting values of the visible light dielectric constants. We have recalculated these widely used polarisabilities using the more accurate room-temperature dielectric constant data of Lowndes and Martin and a better minimisation procedure of Pirenne and Kartheuser. We have also calculated for the first time the low temperature values of these polarisabilities. The computed values of the polarisability in ų are Li⁺ 0·029, Na⁺ 0·285, K⁺ 1·149, Rb⁺ 1·707, Cs⁺ 2·789, F^? 0·876, Cl^? 3·005, Br^? 4·168, I^? 6·294 at 300°K and Li⁺ 0·029, Na⁺ 0·290, K⁺ 1·133, Rb⁺ 1·679, Cs⁺ 2·743, F^? 0·858, Cl^? 2·947, Br^? 4·091, I^? 6·116 at 4°K. The relative standard deviations for all the alkali halides are 1·20 and 1·43 per cent at 300°K and 4°K respectively justifying the additive nature of the individual ion polarisabilities.     

Mössbauer studies of 151Eu in europium oxalate, europium bissalen ammonium and europium benzoate

Although a number of europium water insoluble chelates have been prepared for several decades, the covalent nature of these compounds has never been established in any quantitative fashion. Shifts in the I.R. bands and conductivity measurements of these salts were hitherto used to qualitatively compare their molecular nature. In this communique we have used temperature coefficients of ¹⁵¹Eu Mössbauer spectra to determine the Debye temperatures (θ _D) of three europium chelates: namely europium oxalate, europium bissalen ammonium (recently reported) and europium benzoate and compared their θ _D with the measured θ _D of the known ionic EuF₃. Additionally, the mean square amplitude (<x ²) of these four compounds was computed and plotted as a function of temperature giving in each case a reasonable linear plot. It was interesting to note that the θ _D of the most ionic EuF₃ was greatest (283 ± 10 K) followed by the oxalate (166 ± 15 K), then the europium bissalen ammonium (133 ± 5 K) and lastly the europium benzoate with a θ _D of (105 ± 5 K).     

Measurement of intensities of multiplets in the 2ν3-band of methane at low temperatures

The integrated intensities of the multiplets P(1)–P(10), R(0)–R(9), and of the Q-branch in the 2ν₃-band of ¹²CH₄ have been measured at 102°K, 152°K, 202°K, 251°K, and 300°K. Comparison of our data with theoretical line strengths confirms, at all of the temperatures mentioned, the intensity anomalies observed by Margolis⁽⁵⁾ for lines in this band. The integrated intensity of the 2ν₃-band is found to be S_v = (1·76±-0·04)(300/T (°K)) cm^?2 atm^?1.     

Heat capacity behaviour of Pu−Fe eutectic alloy (10 a/o Fe) between 15 and 373°K. Evidence for order-disorder and an antiphase structure below room temperature

Low temperature heat capacity studies of Pu?Fe eutectic alloy (10 a/o Fe) have suggested the possibility of order-disorder of atoms and an antiphase structure below room temperature. Slow cooling and temperature cycling below 76°K were required for appearance of the postulated antiphase structure. Fermi surface-Brillouin zone boundary interactions are suggested as an explanation for the low temperature behavior of the eutectic alloy as well as for the resistivity maximum in both Pu₆Fe and α-Pu. The best values for S°(298) and {H°(298)?H°(0)} were judged to be 14·20±0·10 cal mol^?1 K^?1 and 1660±30 cal mol^?1.