A wide range of reduced temperatures, in a mesh chosen for ease of interpolation, is covered. Values are given for the classical term and three quantum corrections as well as the first two temperature derivatives of each of these terms. A discussion of the variation of behavior with m, especially at the limits m= 6 and m =∞, is included.

March-April 1971

Tentative set of key values for thermodynamics - Part 1. Report of the ICSU-CODATA Task Group on key values for thermodynamics, October, 1970, S. Sunner, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 2, 97-101 (Mar.Apr. 1971).

Key words: CODATA; key values; thermodynamics.

This paper is a preliminary report from the Task Group on Key Values for Thermodynamics of the Committee on Data for Science and Technology (CODATA) of the International Council of Scientific Unions (ICSU). It gives values agreed upon by the Committee for enthalpies of formation and entropies of 32 atoms, molecules, and ionic species. Sources of the data are also tabulated.

Expanded formulation of thermodynamic scaling in the critical region, M. J. Cooper, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 2, 103-107 (Mar.-Apr. 1971).

Key words: Critical region; equation of state; liquid-gas transition; phase boundary; phase transition; thermodynamic scaling.

A description of the thermodynamic properties in the critical region of a physical system is obtained from a scaled expression for the free-energy F(p, T). In general, a nonsymmetric coexistence curve is predicted, with the symmetric case (e.g., magnets) included as a special example. For fluids, deviations from symmetry give rise to an expression for the average density below the critical point nonlinear in the temperature near Te (in contrast to the usual "law of rectilinear diameter"); these asymmetries also contribute to the discontinuity in the specific heat along the critical isochore. To lowest order, the formulation reduces to Widom's homogeneous scaling; the classical equations of state of the van der Waals type are incorporated as a special case.

Table of spin-orbit energies for p-electrons in neutral atomic (core) np configurations, W. C. Martin, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 2, 109-111 (Mar.-Apr. 1971).

Key words: Atomic spectra; atomic theory; spin-orbit interaction.

Data are given in support of the recently proposed formula Snpn *3=0.45022.33 cm-1 (Z ≥ 5). The table includes evaluations of this formula, which are probably accurate to ~ 15 percent for all atoms Z = 10 to 90. For many (core) np configurations, the accuracy of Snp rom the formula is greater than that to be expected from fitting the observed levels to intermediate coupling theory.

Heat capacities of cis-1,4-polyisoprene from 2 to 360 K, S. S. Chang and A. B. Bestul, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 2, 113-120 (Mar.-Apr. 1971).

Key words: Annealed and quenched glass; calorimetry; cis1,4-polyisoprene; glass transformation; heat capacity; natural rubber; normal and supercooled liquid; rubber, natural; thermal diffusivity; thermodynamic properties.

Heat capacities of amorphous synthetic cis-1,4-polyisoprene have been determined for the quenched and annealed glasses from 2 to T, (around 200 K) and for the liquid from T, to 360 K,

with a precision of better than 0.05 percent above 15 K. T,, as determined from H versus T plots, is 203 K for the quenched glass and 198 K for the annealed glass. For the glasses the heat capacity values from this research are about 1 percent higher than that reported in 1935 for natural rubber hydrocarbon. For the liquid the result from this research agrees better (within 1 percent) with recently (1967) proposed values than those from the earlier experiment cited. Effects of crystallization and melting, stark rubber crystals, and additives (antioxidants and stabilizers) were also studied.

Combined low-pressure and high-pressure measurements of density and bulk modulus of aviation instrument oil and 2-methylbutane and their mixtures, J. C. Houck and P. L. M. Heydemann, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 2, 121-127 (Mar.-Apr. 1971).

Key words: Bulk modulus; compressibility; density; dilatometric measurements; high pressure; liquids; ultrasonics; 2-methylbutane.

Dilatometric measurements were made on mixtures of aviation instrument oil and 2-methylbutane at low pressures. These results are combined with previous dilatometric and ultrasonic measurements at high pressures to give density, relative volume, and isothermal bulk modulus of the mixtures to pressures of 20 kilobars. The ratio of the adiabatic bulk modulus to isothermal bulk modulus for 2-methylbutane is also given.

Crystal structure of Ca2Na2(CO3)3 (shortite), B. Dickens, A. Hyman, and W. E. Brown, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 2, 129-135 (Mar.-Apr. 1971).

Key words: Calcium sodium carbonate; crystal structure; shortite; single-crystal x-ray diffraction.

Ca2Na2(CO3)3 crystallizes in the orthorhombic unit cell a= 4.947(1) Å, b = 11.032(2) Å, and c=7.108(1) Å at 25 °C with two formula weights in space-group Amm2. The structure has been redetermined, corrected, and refined to Ru=0.025, R= 0.020 using 684 "observed" x-ray reflections from a single crystal. Corrections were made for absorption and isotropic extinction. In the extinction refinements, r refined to 0.00017(1) cm. The structure consists of Ca2NaCO3 layers interleaved with Na(CO3)2 layers. The Ca ion is coordinated strongly to nine oxygens, including three CO, edges, with Ca... O distances varying from 2.401(2) Å to 2.576(2) Å. One Na ion is coordinated strongly to eight oxygens, including two CO, edges, with Na... O distances from 2.429(2) Å to 2.605(1) Å. The other Na ion is coordinated strongly to six oxygens. including one CO, edge, at 2.296(1) Å to 2.414 Å, and weakly to a seventh at 3.050(3) Å. One CO3 group is coordinated to seven cations, the other is coordinated to eight. The CO3 groups have seemingly maximized their edge sharing with Ca ions rather than Na ions.

May-June 1971

The solid phase photolysis and radiolysis of ethylene at 20 to 77 K, R. Gorden, Jr., and P. Ausloos, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 141-146 (May-June 1971).

Key words: Ethylene; free radical reactions; ion-molecule reactions; photolysis; polymerization; radiolysis.

Films of ethylene condensed onto a cold finger maintained at 20 K were irradiated with photons whose energy ranged from 8.4 to 21.2 eV. At the higher photon energies the relative yields of products compare well with those seen in the radiolysis of solid ethylene. Experiments on CH2CD2 demonstrate that in the photolysis hydrogen is mainly formed by the elimination processes CH2CD,* H2(D2)+C2D2(C2H2) and CH2CD2*· HD+C2HD. The relative probabilities of these three processes

are independent of the energy of the incident photons from 8.4 to 11.6 eV and are within experimental error identical to those observed in earlier gas phase photolysis experiments. Relative to acetylene, cyclobutane is a minor product at 8.4 eV but increases by an order of magnitude at higher energies where ions play a role. Cyclobutane, 1-butene and methylcyclopropane formed upon irradiation of frozen C2H-C2D1 mixtures consisted mainly of C4D8, C4D4H4, and C4H8. Plausible mechanisms which may account for the formation of the latter products are examined. In the solid phase as in the gas phase the relative importance of H-atom production is seen to increase with increasing photon energy. Cyclopropane, apparently formed by insertion of CH2 into C2H4, is observed as a product at all wavelengths in the photolysis, and in the radiolysis.

Kinetic mass spectrometric investigation of the ion-molecule reactions occurring in C, and C, alkanes following photoionization at 106.7 and 104.8 nm, L. W. Sieck, S. K. Searles, and P. Ausloos, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 147-153 (May-June 1971).

Key words: Gas phase; hydrocarbons; ion-molecule reactions; mass spectrometry; photoionization; rate constants. The photoionization of C, and Cs alkanes has been investigated at 106.7 and 104.8 nm in a mass spectrometer specifically designed for the investigation of ion-molecule reactions occurring at thermal kinetic energies. Absolute rate constants are reported for the reactions of various fragment ions with the corresponding parent molecule.

The rate constants found for reactions of sec-C3H7+ ions with i-C4H10, n-C4H10, i-C5H12, and n-C5H12 were found to be 3.3, 4.4, 4.7, and 5.2 × 10-10 cm3/molecule-second respectively. The C4H9+ ions were also found to be highly reactive, exhibiting rate constants of 3.6 and 3.8 × 10-10.cm3/molecule-second in reactions with i-C5H12 and n-C5H12. The rate constants for reaction of C3H6+ with i-C4H10, n-C4H10, i-C5H12, and n-C5H12 were found to be 4.9, 4.9. 7.6, and 7.9 × 10-10 cm3/molecule-second, respectively. Butene ions are less reactive by an order of magnitude. The results are compared with complementary data derived from electron impact experiments, and the relationship between the structure and reactivity of the various ions is discussed.

An alumina standard reference material for resonance frequency and dynamic elastic moduli measurement. I. For use at 25 °C, R. W. Dickson and J. B. Wachtman, Jr., J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 155-162 (May-June 1971).

Key words: Alumina; elastic modulus; resonance frequency; shear modulus; standard reference material; Young's modulus.

Bars of sintered polycrystalline alumina were machined to nominal dimensions of 12.7 by 1.27 by 0.32 cm. Surfaces were machined flat and parallel. The mass, dimensions, and resonance frequencies (flexural and torsional) were measured at 25 °C. The exact frequency is specified for each bar and is typically about 2030 Hz for flexural resonance and 11250 Hz for torsional resonance. The effect of suspension loading on resonance frequency was determined and a correction made. Each bar can be used as a frequency standard with an uncertainty for values measured in air of about ± 0.03 Hz for flexure and ± 0.08 Hz for torsion. The effect of atmosphere on resonance frequency was determined and a correction was made for this effect. The uncertainty for resonance frequencies in vacuum is about ± 0.06 Hz for flexure and ± 0.18 Hz for torsion. Each bar can also be used as a dynamic elasticity standard with an uncertainty estimated to be about 0.2 percent for the shear modulus and 0.4 percent for Young's modulus.

Optical and mechanical properties of some neodymium-doped laser glasses, R. M. Waxler, G. W. Cleek, I. H. Malitson, M. J.

Dodge, and T. A. Hahn, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 163-174 (May-June 1971).

Key words: Chemical composition; density; glasses; hardness; laser; optical homogeneity; photoelasticity; refractive index; thermal conductivity; thermo-optic properties; transmittance.

Studies have been made to evaluate thermo-optic and piezooptic properties of five laser glasses. Measurements were made at the Cd red line, λ=0.6438 μm, over a wide range of temperatures and pressures using interferometric and polarimetric techniques. The refractive index-temperature data show both positive and negative values and small changes with temperature. The changes in index with applied compressive stress are positive in value. Other optical properties evaluated were homogeneity, transmittance, and refractive index as a function of wavelength. An ultrasonic pulse-echo technique was used to determine the elastic constants, Young's modulus, shear modulus, bulk modulus, and Poisson's ratio. Data for thermal expansion, thermal conductivity, density, hardness and chemical composition are also given. Calculations were made of the thermal change of refractive index at constant volume. These data can be used to calculate corrections for the distortions of the wavefront of light generated in lasers.

Effect of environment on viscous flow in inorganic oxide glasses, J. H. Simmons and P. B. Macedo, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 175-184 (May-June 1971).

Key words: Critical point theories; immiscibility; phase transitions; structural relaxation; transport phenomena; viscous flow.

Results from viscosity and shear structural relaxation measurements conducted above the liquid-liquid phase transition of a series of immiscible inorganic oxide glasses are analyzed. A model is proposed which relates the temperature dependence of the complex modulus and viscosity to the behavior of microstructure in the glass resulting from supercritical fluctuations in composition. It is suggested that the critical microstructure induces differences in local environment in the glass which in turn cause the appearance of distributions of relaxation times. The model is formulated using elementary fluctuation theory and the resulting equations are successfully compared to the data. Phase relations in the SrO-IrO2-Ir system in air, C. L. McDaniel and S. J. Schneider, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 185-196 (May-June 1971).

Key words: Dissociation; equilibrium; phase relations;
SrO:IrO2 compounds; SrO-IrO2-Ir system.

The equilibrium phase relations for the SrO-IrO2-Ir system were determined in an air environment at atmospheric pressure. A ternary equilibrium phase diagram was constructed indicating selected oxygen reaction lines and tie lines. A binary representation is given for the ternary system in air. Of the nine phases detected in this study, three are stable and six are probably metastable under atmospheric conditions. The stable compounds, 4SrO·IrO2, 2SгO·IrO2, and SÃO IrO2 dissociate at 1540, 1445, and 1205 °C, respectively. The metastable phases include low-4SrO IrO2, 2Sr0-3IrO2, xSrO IrO2(x > 2), ySrO IrO2(4 > y > 2), zSrO·IrO2(2 > z > 1), and 3SrO-2IrO2. The specific composition of the metastable phases could not be ascertained with certainty. The x-ray patterns of all phases detected in this study were indexed with the exception of that of the zSrO IrO2(2 >z> 1) compound. A summary of x-ray data is given for all known phases occurring in the system.

The crystal structure of BaCa(CO3)2 (barytocalcite), B. Dickens and J. S. Bowen, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 197-203 (May-June 1971).

Key words: Aragonite; barium calcium carbonate; calcium carbonate; crystal structure; single crystal x-ray diffraction.

The barytocalcite phase of BaCa(CO3)2 crystallizes in the monoclinic unit cell a=8.092(1) Å, b=5.2344(6) Å, c= 6.544(1) Å, B=106.05(1)° at 25 °C with cell contents of 2[BaCa(CO3)2]. The structure previously reported by Alm is correct in its coarse details but has been redetermined here and refined to R=0.028, R=0.023 in space-group P21/m using 1652 observed reflections. Corrections were made for absorption, isotropic extinction, and anomalous dispersion.

The structure of barytocalcite has an ... ABCABC ... stacking of cation layers and repeat every 3 layers. The calcite phase of CaCO3 has an ABC cation layer sequence and repeats every 6 layers. The orientations of the CO3 groups in barytocalcite are like the CO3 group orientation in the aragonite phase of CaCO3, and are rotated about 30° from the CO3 group orientation in calcite. The cation layer sequence in aragonite is ... ABAB... and the structure repeats every 2 layers.

The Ca ion in barytocalcite is coordinated to seven oxygens, including an edge of a CO3 group, with Ca... O distances in the range 2.305(2) Å to 2.518(2) Å. The Ba ion is coordinated to five edges and one apex of the CO3 groups with Ba... O distances ranging from 2.729(3) Å to 3.140(2) Å. The distances of the C atoms in the CO3 groups from the planes of the O atoms are 0.025(5) Å and 0.022(4) Å for C(1) and C(2), respectively.

Ionization of hydrofluoric acid at 25 °C, P. R. Patel, E. C. Moreno, and J. M. Patel, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 205-211 (May-June 1971).

Key words: Hydrofluoric acid; ionization constant; lanthanum fluoride electrode; least squares procedure; potentiometric measurements.

The ionization constant, K1, for the reaction HF H+ + Fwas calculated on the basis of potentiometric measurements in the cell Ag; AgCl, Cl-, F-||LaF3||NaF, HCl, H2O|KCI(Satd.), Hg2Cl2; Hg at 25 °C. A least squares procedure was applied to the experimental data yielding a best estimate for K, of 5.85 x 10-4 with a standard error of 0.03 × 10-4.

Vapor pressure equation for water in the range 0 to 100 °C, A. Wexler and L. Greenspan, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 3, 213-230 (May-June 1971).

Key words: Clausius-Clapeyron equation; saturation vapor pressure over water; steam; vapor pressure; vapor pressure of water; virial coefficients; water vapor.

Some precise measurements of the vapor pressure of liquid water at seven temperatures in the range 25 to 100 °C were reported recently by H. F. Stimson of NBS. These measurements have an estimated standard deviation of 20 ppm or less, except at 25 °C where the estimated standard deviation is 44 ppm. We have derived a formula which yields computed values of vapor pressure agreeing with Stimson's measurements to within 7 ppm.

We integrated the Clausius-Clapeyron equation using the accurate calorimetric data of Osborne, Stimson, and Ginnings and the Goff and Gratch formulations for the virial coefficients of water vapor to obtain an equation that has a rational basis. This equation was then adjusted to bring it into closer accord with Stimson's pressure measurements. Two tables are given of the vapor pressure, expressed in pascals, as a function of temperature at 0.1-deg intervals over the range 0 to 100 °C, one on the International Practical Temperature Scale of 1948 and the other on the International Practical Temperature Scale of 1968.

July-August 1971

Inclusions in laser materials, H. S. Bennett, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 247-260 (JulyAug. 1971).

Key words: Antimony; heat conduction; laser materials; Nd-doped glass; platinum; stress components; thermoelastic theory.

One of the severe problems encountered in high-power-solidstate laser systems is the thermal damage to laser rods and optical elements. One such type of damage is thought to arise from metallic or dielectric inclusions; i.e., impurities with physical and optical properties which differ substantially from those of the host material. Such inclusions may absorb an appreciable amount of the incident radiation and thereby may undergo thermal expansion. This produces major stresses within the host material. Estimating such thermal properties requires the consideration of solutions to the heat diffusion equation and to the thermal stress equations with appropriate boundary conditions. The optical path length change for a probing light ray passing near the inclusion, the radial and tangential stress components, and the changes of the refractive index for radially polarized and tangentially polarized light due to the thermal stress field are computed. The dependence of the maximum value of the tensile stress upon the size of the inclusion and upon the physical properties of the host is examined. The feasibility of using optical techniques to detect metallic and dielectric inclusions in laser materials before they cause damage also is studied. The computations suggest that the use of laser pulse widths of the order of microseconds or longer may be more promising for the detection of small incipient absorbing centers than the use of nanosecond pulse widths.

Heat diffusion near absorbing centers in laser materials, H. S. Bennett, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 261-268 (July-Aug. 1971).

Key words: Absorbing center; complementary error function; heat diffusion; laser host.

The solutions to the heat diffusion equation for spherical absorbing centers in laser materials are presented. The ratio of the volume specific heats for the absorbing center and the laser host is found to determine three regions of behavior. Series expansions for small times and for very large times also are given in each of the three regions. Rapidly converging representations for the complementary error function of complex arguments are developed in order to evaluate numerically the region for which the volume specific heat ratio is greater than three fourths. Thermal conductivity, electrical resistivity, and thermopower of aerospace alloys from 4 to 300 K, J. G. Hust, D. H. Weitzel, and R. L. Powell, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 269-277 (July-Aug. 1971).

Key words: Aluminum alloy; cryogenics; electrical resistivity; Lorenz ratio; nickel alloys; Seebeck effect; thermal conductivity; titanium alloy; transport properties.

Thermal conductivity, electrical resistivity, and thermopower have been measured for several aerospace alloys: titanium alloy A110-AT, aluminum alloy 7039, Inconel 718, and Hastelloy X. Tables and graphs of the measured properties and Lorenz ratio are presented over the range 4 to 300 K. Comparisons to other measurements and theoretical analysis of the data are included. The uncertainties of the property data are estimated as (1) 0.7 to 2.5 percent for thermal conductivity, (2) 0.25 percent in electrical resistivity, and (3) about 0.1μV/K in thermopower. Refractive indices of fused silica at low temperatures, R. M. Waxler and G. W. Cleek, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 279-281 (July-Aug. 1971).

Key words: Fused silica; glasses; interferometry; optics; refractive index.

The refractive indices of a commercial fused silica specimen were determined at ten wavelengths from 404.7 to 667.8 nm over the temperature range from 200 to +20 °C. The data are needed for the design of optical systems for space applications where the extremes of temperature are encountered. Values of the thermal coefficient of refractive index were found to be positive and varied from about 9 × 10-6/°C at room temperature to 3 x 10-6°C at liquid nitrogen temperature. The data also showed that there is an increase in dispersion with increasing temperature. These results bear out the predictions of the theory for the thermo-optic behavior of solids.

High-speed (subsecond) measurement of heat capacity, electrical resistivity, and thermal radiation properties of tungsten in the range 2000 to 3600 K, A. Cezairliyan and J. L. McClure, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 283-290 (July-Aug. 1971).

Key words: Electrical resistivity; emittance; heat capacity; high-speed measurements; high temperature; thermal radiation properties; thermodynamics; tungsten.

Measurements of heat capacity, electrical resistivity, hemispherical total emittance, and normal spectral emittance of tungsten above 2000 K by a pulse heating technique are described. Duration of an individual experiment, in which the specimen is heated from room temperature to near its melting point, is less than one second. Temperature measurements are made with a photoelectric pyrometer. Experimental quantities are recorded with a digital data acquisition system, which has a full-scale signal resolution of one part in 8000. Time resolution of the entire system is 0.4 ms. Results on the above properties of tungsten in the range 2000 to 3600 K are reported and are compared with those in the literature. Estimated inaccuracy of measured properties in the above temperature range is: 2 to 3 percent for heat capacity, 1 percent for electrical resistivity, 3 percent for hemispherical total and normal spectral emittances.

The calculated continuous emission of a LTE hydrogen plasma, J. R. Roberts and P. A. Voigt, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 291-333 (July-Aug. 1971).

Key words: Emission coefficient; hydrogen; hydrogen continuum; LTE; spectral radiance standard; Stark-broadening. The total continuous emission coefficient for a LTE hydrogen plasma at one atmosphere is calculated for a temperature range from 8000 to 16000 K and a wavelength range from 400 to 15000 Å. Contributions involving the species H, H2+, H−, and H2, as well as the wings of Stark-broadened hydrogen lines are included. This calculation will permit the radiation emitted from a laboratory hydrogen plasma to be used as a high intensity spectral radiance calibration standard.

The second spectrum of nickel (Ni 11) (addenda and errata), A. G. Shenstone, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 335-336 (July-Aug. 1971).

Key words: Energy levels; ionization potential; nickel; spectral series; spectroscopy; wavelength.

This paper provides additional information which came to light too late for the original publication [J. Res. Nat. Bur. Stand. (U.S.) 74A, 801 (1970)].

Tables of second virial coefficients and their first and second derivatives for the Stockmayer (m, 6, 3) potential function, J. S. Gallagher and M. Klein, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 4, 337-385 (July-Aug. 1971).

Key words: Dipole; gas; intermolecular potential function; polar; second virial coefficient; Stockmayer.

Expressions are developed for the second virial coefficient and its first two temperature derivatives for polar molecules on the Stockmayer model of a dipole imbedded in a spherical core. In the case considered, the core molecules interact according to an (m, 6) intermolecular potential function. Terms describing the dependence of these quantities on the polarizability of the dipole are also included. Tables are given for the cases m=9, 12, 18, 24, 36, and 60. These tables can be used to calculate the first density corrections to all of the thermodynamic properties of a fluid of polar molecules. The adequacy and accuracy of the tables are discussed in some detail.

September-October 1971

Measurement of the relative enthalpy of pure a-Al2O3 (NBS heat capacity and enthalpy standard reference material No. 720) from 273 to 1173 K, D. A. Ditmars and T. B. Douglas, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 401420 (Sept.-Oct. 1971).

Key words: Alumina; aluminum oxide; corundum; drop calorimetry; enthalpy; heat capacity standard; specific heat; standard reference material; synthetic sapphire; thermodynamic functions.

The relative enthalpy of NBS Standard Reference Material No. 720 (99.98 percent pure, single-crystal a-Al2O3, a calorimetric heat-capacity standard) was measured over the range 273 to 1173 K by the drop method using a highly precise Bunsen ice calorimeter. Enthalpy data over the same temperature interval were obtained also on the Calorimetry Conference Sample of this substance. These results are believed to be more accurate than similar NBS results on the latter sample published in 1956, and show no significant discontinuity with the NBS data on the same substance that covered the ranges 13 to 380 K and 1173 to 2257 K. The average deviation from the mean for all enthalpy measurements on the SRM 720 sample was 0.017 percent, and the smooth enthalpy values derived from the data were estimated to be accurate to 0.1 percent. The precautions observed in order to minimize measuring errors are described in detail. The data are compared with many sets of the most reliable published data available and new recommended values for the thermodynamic functions of a-Al2O3 are presented for the interval 0 to 1200 K. High-precision coulometric titrations of boric acid, G. Marinenko and C. E. Champion, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 421-428 (Sept.-Oct. 1971).

Key words: Accurate analysis; boric acid; coulometric titration; high-precision acidimetry; high-precision coulometry. An absolute method was developed for the determination of boric acid by coulometric titrimetry. The precision of the method, expressed as the standard deviation of a single determination is 0.0033 percent. Changes in the investigated titration parameters produced no significant effects on the titration results. Indications are that within the uncertainty of measurements the method is bias free.

Determination of trace elements in ruby laser crystals by neutron activation analysis, B. A. Thompson and E. C. Miller, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 429433 (Sept.-Oct. 1971).

Key words: Activation analysis; Al2O3; interfering reactions; laser; nondestructive analysis; ruby; trace elements. Methods are described by which concentration levels have been determined for up to ten different trace elements and upper limits established for over 40 additional elements at the parts per million level or below in ruby crystals using neutron activation analysis. This information is required to determine the effect of trace element levels on laser performance. With conventional

analytical methods difficulties arise because of both the refractory and insulating properties of the material. Because the crystals cannot be readily dissolved, the activation analysis was carried out nondestructively, irradiating the samples with highly thermalized neutrons to minimize formation of 24Na and 27Mg from (n, a) and (n, p) reactions on the Al2O, matrix, and using a 47cm3 Ge(Li) detector.

Crystallography of some double sulfates and chromates, H. F. McMurdie, M. C. Morris, J. deGroot, and H. E. Swanson, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 435439 (Sept.-Oct. 1971).

Key words: Chromates; langbeinites; lattice constants; sulfates; Tutton salts.

New information is given on cell parameters, density and methods of preparation of 50 compounds of the langbeinite and Tutton salt groups. The langbeinites have the general formula (A+)2(B2+)2(XO4)3 and the Tutton salts the general formula (A+)2(B2+)(XO4)2 6H2O, where A is K, Rb, (NH4), Tl or Cs; B is Mg, Ni, Cu, Co, or Zn; and X is S or Cr. A comprehensive list of references on the crystallography of the compounds is included.

Discrimination between equations of state, J. R. Macdonald and D. R. Powell, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 441-453 (Sept.-Oct. 1971).

Key words: Curve fitting; data analysis; equations of state; model discrimination; surface fitting.

Eight isothermal equations of state are analyzed to yield quantitative measures of the degrees to which equation pairs can be discriminated for real data, data of limited span and precision. Calculated curves allow one to assess the span and precision necessary in P-V data to allow unambiguous discrimination of various pairs. Some discussion is presented of bias and systematic error which may arise in least squares fitting. Using exact synthetic data, we also illustrate for seven equation pairs the very large relative systematic errors in parameter and standard deviation estimates which arise from such fitting of data of limited span with an incorrect but "close" equation model. General conclusions following from these results are discussed. Although the present work is principally concerned with discrimination between equations of state, its results are pertinent to the more general problem of choosing a "best" analytical model (linear or nonlinear) to represent experimental results.

New absorption bands and isotopic studies of known transitions in CO, J. D. Simmons and S. G. Tilford, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 455-467 (Sept.-Oct. 1971).

Key words: Absorption spectrum; CO; electronic transitions; rotational analysis; vibrational analysis; vibrational and rotational constants.

Several new absorption bands of the a' 3+ - X'Σ+ and e 3Σ- X1+ transitions in CO have been observed and analyzed. Vibrational levels of both the a' 3+ and e 3 states are now known to within 0.4 eV of their dissociation limits. Isotopic bands of 13C160 in natural abundance have been analyzed for both transitions. The vibrational numbering of the e 3- state must be increased by one unit. New bands of the I1Σ- — X1Σ+ and D1A - X1Σ+ transitions are also reported.

A study of line shape of CO infrared emission lines, J. A. Dowling, S. Silverman, W. S. Benedict, and J. W. Quinn, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 469-479 (Sept.-Oct. 1971).

Key words: Carbon monoxide; collision parameters; equivalent width; flame spectra; line shapes.

The shape of several vibration-rotation lines of CO emitted by a C2H2-O2 flame was investigated. An equivalent width measurement was made using an absorption cell of room temperature CO as an analyzer. Analysis of the data showed that line shapes could be fitted to a Voigt function with shape parameters a between 1.0 and 1.5.

The collision widths of the flame lines, as determined by the shape parameters, are in essential agreement with earlier room temperature measurements. The extrapolation of the widths measured at room temperature to high temperature has been shown to be reliable within the uncertainty of this experiment (+ 15%).

Ionization quantum yields and absorption coefficients of selected compounds at 58.4 and 73.6-74.4 nm, R. E. Rebbert and P. Ausloos, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 481-485 (Sept.-Oct. 1971).

Key words: Absorption coefficient; helium resonance radiation; hydrocarbons; inorganic molecules; ionization efficiency; ionization quantum yield; neon resonance radiation. The ionization quantum yields and the extinction coefficients of a number of compounds have been determined at the wavelengths of the helium (58.4 nm) and neon (73.6-74.4 nm) resonance lamps. These are lamps with thin aluminum windows (100-200 nm) which we inserted in a glass cell backed by a second cell. Both cells are provided with parallel plate electrodes and separated from each other by an aluminum window. The ionization quantum yields are based on ionization efficiency of argon which is unity. Hydrogen, which has an ionization quantum yield of 0.94 and 1.00 at 73.6-74.4 and 58.4 nm respectively, was used as a secondary standard because it yielded better defined saturation ion current plateaus. The extinction coefficients were determined in both a double cell and a single cell arrangement. The agreement between the two measurements was excellent. In general an inert diluent was added to the gas of interest in order to improve the plateau of the saturation ion current. These results are compared with the literature values, which were mainly determined in windowless systems with monochromators.

Kinetic mass spectrometric investigation of the reactions of tC4H9+ ions with some simple polar molecules at thermal energies, L. Hellner and L. W. Sieck, J. Res. Nat. Bur. Stand. (U.S.), 75A (Phys. and Chem.), No. 5, 487-493 (Sept.-Oct. 1971).

Key words: Ion molecule reactions; mass spectrometry; neopentane; photoionization; proton affinity; rate constants. The interactions of t-C4H9+ ions from neopentane with some simple polar molecules have been investigated in a high pressure photoionization mass spectrometer at thermal kinetic energies. Proton transfer was found to occur from t-C4H9+ to acetone, ammonia, and the various methylamines, but not to molecules having estimated proton affinities < 195 kcal/mol (815 kJ/mol). Macroscopic thermal rate coefficients are reported for the various proton transfer reactions, all of which are on the order of 10-9 cm3/molecule second. The reaction