CODATA Task Group Research Articles

Heat Capacity of Reference Materials: Cu and W

The CODATA Task Group on Thermophysical Properties is preparing a set of recommended values for the heat capacity, thermal expansion, and transport properties of key solids which are used in calibrating or checking measuring equipment. The present paper surveys selected data on heat capacity at constant pressure Cp of copper from 1 to 1300 K and tungsten from 1 to 3400 K. Selected values are tabulated for Cp and also for heat capacity at constant volume Cv. Interpolating functions are given for Cp.

Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry: Supplement II. CODATA Task Group on Gas Phase Chemical Kinetics

This paper updates and extends previous critical evaluations of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in atmosphere chemistry [J. Phys. Chem. Ref. Data 9, 295 (1980); 11 327 (1982)]. The work has been carried out by the authors under the auspices of the CODATA Task Group on Gas Phase Chemical Kinetics. Data sheets have been prepared for 256 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction, a preferred value of the rate coefficient at 298 K is given together with a temperature dependence where possible. The selection of the preferred value is discussed; and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an appendix listing the available data on enthalpies of formation of the reactant and product species.

Standard reference materials to test thermal diffusivity measurement equipments

The importance of the availability of Standard Reference Materials (SRM) to improve the accuracy of thermal diffusivity measurements is shown in the example of the modulated-light heating-beam technique. Systematic examinations of error sources led to the result that SRMs with conduction and radiation properties similar to the material to be investigated are useful for accurate measurements. Three types of SRM were investigated within the framework of the CODATA task group on thermophysical properties—graphite, refractory metal and stainless steel. Poco AXM-5Q1 graphite and austenitic Nb-stabilised steel 16Cr20Ni could be proved to be well suited relative to the reproducibility and stability of their thermal diffusivities. Measurement results of our own and of some other participants agreed with less than 2% deviation in the temperature range 1500 K to 2300 K for Poco graphite, and between 800 K and 1300 K for austenitic stainless steel. Such a good agreement could not be found with the third SRM, arc-cast tungsten; however, there are not enough data available within the CODATA programme for a final statement. Comparative measurements on Poco graphite have shown that, for the extrapolation of the results from one manufacturing lot to another, a deviation of the thermal diffusivity of at least 8% must be taken into consideration.

Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry: Supplement I CODATA Task Group on Chemical Kinetics

This paper updates and extends a previous critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10–55 km altitude) [J. Phys. Chem. Ref. Data 9, 295 (1980)]. The work has been carried out by the authors under the auspices of the CODATA Task Group on Chemical Kinetics. Data sheets have been prepared for 228 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction a preferred value of the rate coefficient at 298 K is given together with a temperature dependence where possible. The selection of the preferred value is discussed, and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an appendix listing the available data on enthalpies of formation of the reactant and product species.

Forthcoming Conference on Fundamental Constants

The Second International Conference on Precision Measurement and Fundamental Constants will be held 8–12 June 1981 at the National Bureau of Standards (NBS), Gaithersburg, Maryland. This Conference will be similar to that held at NBS Gaithersburg in August 1970: It will provide an international forum for those engaged in experimental and theoretical research on precision measurements relating to the fundamental physical constants, and on the testing of related fundamental theory. The topics of interest include: High accuracy mass measurements and the kilogram Absolute realizations of the basic electric units Frequency and time standards Frequency measurements of optical radiation, the speed of light and the unit of length Faraday and Avogadro constants Proton gyromagnetic ratio Proton magnetic moment in Bohr and nuclear magnetons Fine and hyperfine structure in simple atoms such as hydrogen, muonium, positronium and helium Rydberg constant Proton to electron mass ratio Lepton magnetic moment anomalies Fine-Structure constant High precision tests of QED Newtonian gravitational constant and gravitational acceleration Eötvös experiments, anisotropy of space, high precision tests of relativity Gas and Stefan-Boltzmann constants Time variation of the constants Assignment of uncertainties to determinations of constants Lease-squares adjustments of the constants. It is expected that new results reported at the Conference will be considered for inclusion in the next least-squares adjustment of the constants which is being carried out under the auspices of the CODATA Task Group on Fundamental Constants. This adjustment should be completed by the end of 1981 and the resulting set of recommended values officially adopted for international use by CODATA in early 1982.Those interested in the Conference should communicate with Dr B N Taylor, National Bureau of Standards, Building 220, Room B 258, Washington, DC 20234, USA.

CODATA Task Group on thermophysical properties of solids

CODATA Task Group on thermophysical properties of solids

Evaluated kinetic and photochemical data for atmospheric chemistry

This paper contains a critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10–55 km altitude). The work has been carried out by the authors under the auspices of the CODATA Task Group on Chemical Kinetics. Data sheets have been prepared for 148 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction a preferred value of the rate coefficient at 298 K is given together with a temperature dependency where possible. The selection of the preferred value is discussed, and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an Appendix listing the available data on enthalpies of formation of the reactant and product species.

CODATA recommended key values for thermodynamics, 1973 Report of the CODATA Task Group on key values for thermodynamics, November 1973

CODATA recommended key values for thermodynamics, 1973 Report of the CODATA Task Group on key values for thermodynamics, November 1973

Table of fundamental constants is updated

An adjusted set of values for the fundamental constants has been recommended for international adoption by E. Richard Cohen and Barry N. Taylor. These values were worked out under the auspices of the International Council of Scientific Union's CODATA Task Group on Fundamental Constants; they therefore represent the first internationally “official” adjustment ever carried out. The complete Taylor–Cohen report appears in the Journal of Physical and Chemical Reference Data; a card listing the recommended values may be found opposite page 81. Both Cohen (Rockwell International, Thousand Oaks, California) and Taylor (US National Bureau of Standards, Gaithersburg, Maryland) have previously done semiofficial and widely used adjustments; the most recent work of Cohen and Jesse W. M. DuMond appeared in 1963 and that of Taylor, William H. Parker and Donald N. Langenberg in 1969.

The enthalpy of solution of gaseous hydrogen iodide in water, and the relative apparent molar enthalpies of hydriodic acid

The standard enthalpy change for solution of gaseous hydrogen iodide in water was found by direct solution calorimetry to be ΔH soln o(298.15K) = −(19905 ± 20) cal th mol −1. This result confirms the difference between the values for ΔH f o(HI, g) and ΔH f o(HI, aq) selected by the CODATA task group. In addition, values for L φ , the relative apparent molar enthalpy, were obtained over the molality range 0 to 18 mol kg −1 from measurements of enthalpies of dilution.

The 1973 Least-Squares Adjustment of the Fundamental Constants

This paper is a summary of the 1973 least-squares adjustment of the fundamental physical constants carried out by the authors under the auspices of the CODATA Task Group on Fundamental Constants. The salient features of both the input data used and its detailed analysis by least-squares are given. Also included is the resulting set of best values of the constants which is to be recommended for international adoption by CODATA, a comparison of several of these values with those resulting from recent past adjustments, and a discussion of current problem areas in the fundamental constants field requiring additional research.

An announcement by the CODATA Task Group on key values for thermodynamics

An announcement by the CODATA Task Group on key values for thermodynamics