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Top 20 Most Read Articles
July 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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Experimental Vibrational Zero-Point Energies: Diatomic Molecules J. Phys. Chem. Ref. Data 36, 389 (2007); http://dx.doi.org/10.1063/1.2436891 (9 pages) Online Publication Date: 18 April 2007
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Vibrational zero-point energies (ZPEs), as determined from published spectroscopic constants, are derived for 85 diatomic molecules. Standard uncertainties are also provided, including estimated contributions from bias as well as the statistical uncertainties propagated from those reported in the spectroscopy literature. This compilation will be helpful for validating theoretical procedures for predicting ZPEs, which is a necessary step in the ab initio prediction of molecular energetics.
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Physical Properties of Ionic Liquids: Database and Evaluation J. Phys. Chem. Ref. Data 35, 1475 (2006); http://dx.doi.org/10.1063/1.2204959 (43 pages) Online Publication Date: 10 October 2006
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A comprehensive database on physical properties of ionic liquids (ILs), which was collected from 109 kinds of literature sources in the period from 1984 through 2004, has been presented. There are 1680 pieces of data on the physical properties for 588 available ILs, from which 276 kinds of cations and 55 kinds of anions were extracted. In terms of the collected database, the structure-property relationship was evaluated. The correlation of melting points of two most common systems, disubstituted imidazolium tetrafluoroborate and disubstituted imidazolium hexafluorophosphate, was carried out using a quantitative structure-property relationship method.
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Spectroscopic Data for Neutral Francium (Fr I) J. Phys. Chem. Ref. Data 36, 497 (2007); http://dx.doi.org/10.1063/1.2719251 (11 pages) Online Publication Date: 21 May 2007
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Energy levels and hyperfine structure constants have been compiled for the sixteen longest lived isotopes of francium (Z = 87). For most isotopes with atomic weights in the range 199 ≤ A ≤ 232 the only measurements made are for the 7s
 and 7p  levels. Additional energy-level data are available for  ,  , and  . Wavelengths with classifications and transition probabilities are tabulated for . In addition, the ionization energy is included for isotopes for which a sufficient number of levels have been measured, and . |
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Handbook of Basic Atomic Spectroscopic Data J. Phys. Chem. Ref. Data 34, 1559 (2005); http://dx.doi.org/10.1063/1.1800011 (701 pages) Online Publication Date: 28 September 2005
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© 2005 American Institute of Physics. |
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J. Phys. Chem. Ref. Data 36, 685 (2007); http://dx.doi.org/10.1063/1.2391321 (47 pages) Online Publication Date: 6 July 2007
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The mutual solubilities and related liquid–liquid equilibria of C8–C17 alcohols with water are exhaustively and critically reviewed. Reports of experimental determination of solubility in 21 chemically distinct binary systems that appeared in the primary literature prior to the end of 2004 are compiled. For 12 systems sufficient data are available to allow critical evaluation. All data are expressed as mass percent and mole fraction as well as the originally reported units. In addition to the standard evaluation criteria used throughout the Solubility Data Series, a new method based on the evaluation of the all experimental data for a given homologous series of saturated alcohols was used.
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J. Phys. Chem. Ref. Data 36, 1 (2007); http://dx.doi.org/10.1063/1.2360986 (18 pages) Online Publication Date: 8 February 2007
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All the currently available experimental permittivity data for pure water are used to derive an interpolation function that precisely represents ε(ν,t,) at standard atmospheric pressure, for frequencies and temperatures in the ranges 0 ⩽ ν ⩽ 25 THz and 0 ⩽ t ⩽ 100 °C. The permittivity data is represented in terms of relaxations and resonances processes. There are three relaxations in the microwave region and two resonances in the far infrared. The temperature dependence of the relaxation and resonance parameters are determined. For example, at 25 °C the three relaxation frequencies are 18.56 GHz, 167.83 GHz, 1.944 THz and the two resonance frequencies are 4.03 and 14.48 THz.
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Atomic Weights of the Elements 2005 J. Phys. Chem. Ref. Data 36, 485 (2007); http://dx.doi.org/10.1063/1.2717223 (12 pages) Online Publication Date: 18 May 2007
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The latest evaluation of atomic weight determinations and other cognate data has warranted 16 changes for the standard atomic weights of the elements, Ar(E), from those published previously in the Table of Atomic Weights 2001. The revised standard atomic weight are as follows: Ar(Al) = 26.981 5386(8), Ar(Bi) = 208.980 40(1), Ar(Cs) = 132.905 4519(2), Ar(Co) = 58.933 195(5), Ar(Au) = 196.966 569(4), Ar(La) = 138.90547(7), Ar(Mn) = 54.938 045(5), Ar(Nd) = 144.242(3), Ar(P) = 30.973 762(2), Ar(Pt) = 195.084(9), Ar(Sm) = 150.36(2), Ar(Sc) = 44.955 912(6), Ar(Na) = 22.989 769 28(2), Ar(Ta) = 180.947 88(2), Ar(Tb) = 158.925 35(2), Ar(Th) = 232.038 06(2). A recommendation is made that δ13C values of all carbon-bearing materials be measured and expressed relative to Vienna-Pee Dee Belemnite on a scale normalized by assigning consensus values of −46.6‰ to L-SVEC lithium carbonate and +1.95‰ to NBS 19 calcium carbonate.
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Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry, Organic Species: Supplement VII J. Phys. Chem. Ref. Data 28, 191 (1999); http://dx.doi.org/10.1063/1.556048 (203 pages)
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This paper updates and extends part of the previous data base of critical evaluations of the kinetics and photochemistry of gas-phase chemical reactions of neutral species involved in atmospheric chemistry [J. Phys. Chem. Ref. Data 9, 295 (1980); 11, 327 (1982); 13, 1259 (1984); 18, 881 (1989); 21, 1125 (1992); 26, 521 (1997); 26, 1329 (1997)]. The present evaluation is limited to the organic family of atmospherically important reactions. The work has been carried out by the authors under the auspices of the IUPAC Subcommittee on Gas Phase Kinetic Data Evaluation for Atmospheric Chemistry. Data sheets have been prepared for 171 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each thermal 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. For each photochemical reaction the data sheets list the preferred values of the photoabsorption cross sections and the quantum yields of the photochemical reactions together with comments on how they were selected. 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 values of enthalpies of formation of the reactant and product species. © 1999 American Institute of Physics and American Chemical Society. |
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J. Phys. Chem. Ref. Data 31, 387 (2002); http://dx.doi.org/10.1063/1.1461829 (149 pages) Online Publication Date: 7 June 2002
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In 1995, the International Association for the Properties of Water and Steam (IAPWS) adopted a new formulation called “The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use”, which we abbreviate to IAPWS-95 formulation or IAPWS-95 for short. This IAPWS-95 formulation replaces the previous formulation adopted in 1984. This work provides information on the selected experimental data of the thermodynamic properties of water used to develop the new formulation, but information is also given on newer data. The article presents all details of the IAPWS-95 formulation, which is in the form of a fundamental equation explicit in the Helmholtz free energy. The function for the residual part of the Helmholtz free energy was fitted to selected data for the following properties: (a) thermal properties of the single-phase region (pρT) and of the vapor–liquid phase boundary (pσρ′ρ″T), including the phase-equilibrium condition (Maxwell criterion), and (b) the caloric properties specific isochoric heat capacity, specific isobaric heat capacity, speed of sound, differences in the specific enthalpy and in the specific internal energy, Joule–Thomson coefficient, and isothermal throttling coefficient. By applying modern strategies for optimizing the functional form of the equation of state and for the simultaneous nonlinear fitting to the data of all mentioned properties, the resulting IAPWS-95 formulation covers a validity range for temperatures from the melting line (lowest temperature 251.2 K at 209.9 MPa) to 1273 K and pressures up to 1000 MPa. In this entire range of validity, IAPWS-95 represents even the most accurate data to within their experimental uncertainty. In the most important part of the liquid region, the estimated uncertainty of IAPWS-95 ranges from ±0.001% to ±0.02% in density, ±0.03% to ±0.2% in speed of sound, and ±0.1% in isobaric heat capacity. In the liquid region at ambient pressure, IAPWS-95 is extremely accurate in density (uncertainty ⩽±0.0001%) and in speed of sound (±0.005%). In a large part of the gas region the estimated uncertainty in density ranges from ±0.03% to ±0.05%, in speed of sound it amounts to ±0.15% and in isobaric heat capacity it is ±0.2%. In the critical region, IAPWS-95 represents not only the thermal properties very well but also the caloric properties in a reasonable way. Special interest has been focused on the extrapolation behavior of the new formulation. At least for the basic properties such as pressure and enthalpy, IAPWS-95 can be extrapolated up to extremely high pressures and temperatures. In addition to the IAPWS-95 formulation, independent equations for vapor pressure, the densities, and the most important caloric properties along the vapor–liquid phase boundary, and for the pressure on the melting and sublimation curve, are given. Moreover, a so-called gas equation for densities up to 55 kg m−3 is also included. Tables of the thermodynamic properties calculated from the IAPWS-95 formulation are listed in the Appendix. © 2002 American Institute of Physics. |
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CODATA Recommended Values of the Fundamental Physical Constants: 1998 J. Phys. Chem. Ref. Data 28, 1713 (1999); http://dx.doi.org/10.1063/1.556049 (140 pages)
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This paper gives the 1998 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. Further, it describes in detail the adjustment of the values of the subset of constants on which the complete 1998 set of recommended values is based. The 1998 set replaces its immediate predecessor recommended by CODATA in 1986. The new adjustment, which takes into account all of the data available through 31 December 1998, is a significant advance over its 1986 counterpart. The standard uncertainties (i.e., estimated standard deviations) of the new recommended values are in most cases about 1/5 to 1/12 and in some cases 1/160 times the standard uncertainties of the corresponding 1986 value. Moreover, in almost all cases the absolute values of the differences between the 1998 values and the corresponding 1986 values are less than twice the standard uncertainties of the 1986 values. The new set of recommended values is available on the World Wide Web at physics.nist.gov/constants. © 1999 American Institute of Physics and American Chemical Society. |
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J. Phys. Chem. Ref. Data 35, 301 (2006); http://dx.doi.org/10.1063/1.2035727 (121 pages) Online Publication Date: 16 February 2006
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Energy levels, with designations and uncertainties, have been compiled for the spectra of the neutral atom and all positive ions of rubidium (Z = 37). Wavelengths with classifications, intensities, and transition probabilities are also tabulated. In addition, ground states and ionization energies are listed. For most ionization stages experimental data are available; however for ionization stages where only theoretical calculations or fitted values exist, these are reported. There are a few ionization stages for which only a calculated ionization potential is available. © 2006 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved. |
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A Fundamental Equation of State for Sulfur Hexafluoride (SF6) in Extended Equation of State Format J. Phys. Chem. Ref. Data 36, 617 (2007); http://dx.doi.org/10.1063/1.2716004 (46 pages) Online Publication Date: 30 May 2007
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An innovative method for the regression of thermodynamic properties of pure fluids was recently proposed. The technique, indicated as an extended equation of state, adopts a framework similar to the extended corresponding states method, but a cubic equation is assumed instead of the equation of state of the reference fluid and the shape functions are expressed through a multilayer feedforward neural network. The use of a neural network assures a very high flexibility of the functional form to be regressed, so the resulting model reaches a representation accuracy which is comparable to that attained by the state-of-the-art multiparameter equations of state in the representation of the thermodynamic properties of a pure fluid. The technique was applied here to sulfur hexafluoride aiming at drawing its dedicated equation of state in a heuristic mode directly from the available experimental data. For sulfur hexafluoride (critical point is at Tc = 318.7232 K and Pc = 3.754 983 MPa), experimental data of several properties in homogeneous states and of properties at phase equilibrium are available. The data approximately cover the range from the triple-point temperature at 223.6 up to 625 K and for pressures up to 60 MPa. The regression procedure was developed on a subset of well distributed density and vapor–liquid coexistence data, the so-called “training set,” and the model was successively validated for all the data sets, including the literature sources reporting values of isobaric heat capacity, speed of sound, and Joule–Thomson coefficient. The obtained results are satisfactory; in fact the proposed equation of state represents the available data within their experimental accuracy.
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J. Phys. Chem. Ref. Data 29, 331 (2000); http://dx.doi.org/10.1063/1.1285884 (55 pages)
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A thermodynamic property formulation for standard dry air based upon available experimental p–ρ–T, heat capacity, speed of sound, and vapor–liquid equilibrium data is presented. This formulation is valid for liquid, vapor, and supercritical air at temperatures from the solidification point on the bubble-point curve (59.75 K) to 2000 K at pressures up to 2000 MPa. In the absence of reliable experimental data for air above 873 K and 70 MPa, air properties were predicted from nitrogen data in this region. These values were included in the determination of the formulation to extend the range of validity. Experimental shock tube measurements on air give an indication of the extrapolation behavior of the equation of state up to temperatures and pressures of 5000 K and 28 GPa. The available measurements of thermodynamic properties of air are summarized and analyzed. Separate ancillary equations for the calculation of dew and bubble-point pressures and densities of air are presented. In the range from the solidification point to 873 K at pressures to 70 MPa, the estimated uncertainty of density values calculated with the equation of state is 0.1%. The estimated uncertainty of calculated speed of sound values is 0.2% and that for calculated heat capacities is 1%. At temperatures above 873 K and 70 MPa, the estimated uncertainty of calculated density values is 0.5% increasing to 1.0% at 2000 K and 2000 MPa. In addition to the equation of state for standard air, a mixture model explicit in Helmholtz energy has been developed which is capable of calculating the thermodynamic properties of mixtures containing nitrogen, argon, and oxygen. This model is valid for temperatures from the solidification point on the bubble-point curve to 1000 K at pressures up to 100 MPa over all compositions. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the real gas contribution, and the contribution from mixing. The contribution from mixing is given by a single generalized equation which is applied to all mixtures used in this work. The independent variables are the reduced density and reduced temperature. The model may be used to calculate the thermodynamic properties of mixtures at various compositions including dew and bubble-point properties and critical points. It incorporates the most accurate published equation of state for each pure fluid. The mixture model may be used to calculate the properties of mixtures generally within the experimental accuracies of the available measured properties. The estimated uncertainty of calculated properties is 0.1% in density, 0.2% in the speed of sound, and 1% in heat capacities. Calculated dew and bubble-point pressures are generally accurate to within 1%. © 2000 American Institute of Physics and American Chemical Society. |
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Recommended Liquid–Liquid Equilibrium Data. Part 3. Alkylbenzene–Water Systems J. Phys. Chem. Ref. Data 33, 1159 (2004); http://dx.doi.org/10.1063/1.1797038 (30 pages) Online Publication Date: 24 January 2005
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The recommended liquid–liquid equilibrium (LLE) data for 21 binary alkylbenzene–water systems have been obtained after critical evaluation of all data (392 data sets) reported in the open literature up to the middle of 2003. An equation for prediction of the alkylbenzene solubilities was developed. The predicted alkylbenzene solubilities were used for calculation of water solubility in the second liquid phase. The LLE calculations were done with the equation of state appended with a chemical term proposed by Góral. The recommended data were presented in the form of individual pages containing tables, all the references, and optionally figures. © 2005 American Institute of Physics. |
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Compilation of Wavelengths, Energy Levels, and Transition Probabilities for W I and W II J. Phys. Chem. Ref. Data 35, 423 (2006); http://dx.doi.org/10.1063/1.1836763 (261 pages) Online Publication Date: 24 February 2006
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Energy levels, wavelengths, and transition probabilities of the first and second spectra of tungsten, W I and W II, have been compiled. Wavelengths of observed transitions and energy levels derived from those wavelengths have been obtained from a critical evaluation of the available literature. Measured transition probabilities for some of the observed transitions have been compiled from the published literature. © 2006 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved. |
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J. Phys. Chem. Ref. Data 36, 399 (2007); http://dx.doi.org/10.1063/1.2383067 (45 pages) Online Publication Date: 7 May 2007
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The solubility and related liquid–liquid equilibria in systems C6 alcohols+water are exhaustively and critically reviewed. Reports of experimental determination of solubility in 13 chemically distinct binary systems that appeared in the primary literature prior to end of 2004 are compiled. 12 systems are available to allow critical evaluation. All data are expressed as mass percent and mole fraction as well as the originally reported units. In addition to the standard evaluation criteria used throughout the Solubility Data Series, a new method based on the evaluation of the all experimental data for a given homologous series of saturated alcohols was used.
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Vibrational and Electronic Energy Levels of Polyatomic Transient Molecules. Supplement B J. Phys. Chem. Ref. Data 32, 1 (2003); http://dx.doi.org/10.1063/1.1497629 (441 pages) Online Publication Date: 18 February 2003
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A summary is presented of recently published, critically evaluated experimental vibrational and electronic energy level data for approximately 1700 neutral and ionic transient molecules and high temperature species possessing from three to sixteen atoms. Although the emphasis is on species with lifetimes too short for study using conventional sampling techniques, there has been selective extension of the compilation to include data for isolated molecules of inorganic species such as the heavy-metal oxides, which are important in a wide variety of industrial chemical systems. Radiative lifetimes and the principal rotational constants are included. Observations in the gas phase, in molecular beams, and in rare-gas and diatomic molecule matrices are evaluated, and several thousand references are cited. The types of measurement surveyed include conventional and laser-based absorption and emission techniques, laser absorption with mass analysis, and photoelectron spectroscopy. © 2003 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved. |
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Solubility of Structurally Complicated Materials: II. Bone J. Phys. Chem. Ref. Data 35, 1653 (2006); http://dx.doi.org/10.1063/1.2360606 (16 pages) Online Publication Date: 29 November 2006
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Bone is a structurally complex material, formed of both organic and inorganic chemicals. The organic compounds constitute mostly collagen and other proteins. The inorganic or bone mineral components constitute predominantly calcium, phosphate, carbonate, and a host of minor ingredients. The mineralized bone is composed of crystals which are closely associated with a protein of which collagen is an acidic polysaccharide material. This association is very close and the protein integrates into the crystalline structure. The mineralization involves the deposition of relatively insoluble crystals on an organic framework. The solubility process takes place when the outermost ions in the crystal lattice breakaway from the surface and become separated from the crystal. This is characteristic for ions dissolving in water or aqueous solutions at the specified temperature. The magnitude of solubility is temperature and pH dependent. Bone is sparingly soluble in most solvents. Enamel is less soluble than bone and fluoroapatite is the least soluble of all apatites in acid buffers. Collagen is less soluble in neutral salt solution than in dilute acid solutions at ambient temperatures. The solubility of collagens in solvents gradually decreases with increasing age of the bone samples.
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Chemical Properties of Electronically Excited Halogen Atoms X(2P1/2) (X = F,Cl,Br,I) J. Phys. Chem. Ref. Data 35, 869 (2006); http://dx.doi.org/10.1063/1.2137724 (60 pages) Online Publication Date: 19 May 2006
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The experimental data on elementary processes (collisional deactivation, chemical reactions, photodissociation) involving spin-orbitally excited X(2P1/2) atoms (X = F,Cl,Br,I) published up to the middle of 2005 are summarized in the present compilation. Critical evaluation of the data and limited comparison to theoretical calculations are also presented. © 2006 American Institute of Physics. |
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Evaluation of Calculated and Measured Electron Inelastic Mean Free Paths Near Solid Surfaces J. Phys. Chem. Ref. Data 28, 19 (1999); http://dx.doi.org/10.1063/1.556035 (44 pages)
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An analysis is given of the consistency of calculated and measured electron inelastic mean free paths (IMFPs) near solid surfaces for electron energies between 50 and 104 eV, the energy range of relevance for surface analysis by Auger electron spectroscopy and x-ray photoelectron spectroscopy. This evaluation is based on IMFPs calculated from experimental optical data and on IMFPs measured by elastic-peak electron spectroscopy (EPES). We describe the methods used for the calculations and measurements, and we identify the various sources of uncertainty. Most of our evaluation is based on IMFPs for seven elemental solids (Al, Si, Ni, Cu, Ge, Ag, and Au) for which there were at least two sources of IMFP calculations and at least two sources of IMFP measurements for each solid. Our comparison of the calculated IMFPs showed a high degree of consistency for Al, Ni, Cu, Ag, and Au. The comparison of measured IMFPs showed greater scatter than for the calculated IMFPs, but reasonable consistency was found for the measured IMFPs of Cu and Ag. The measured IMFPs for four elements (Ni, Cu, Ag, and Au) showed good consistency with the corresponding calculated IMFPs. It is recommended that IMFPs for these four elements (determined from fits of a simple analytic expression to the calculated IMFPs for each element) be used as reference values in future EPES experiments. More limited comparisons have been made of calculated and measured IMFPs for four additional elements (Fe, Mo, W, and Pt) and of calculated IMFPs for six compounds (Al2O3, SiO2, KCl, poly(butene-1-sulfone), polyethylene, and polystyrene). © 1999 American Institute of Physics and American Chemical Society. |
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