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Top 20 Most Read Articles
April 2008
The 20 articles with the most full-text downloads during the month, in descending order.
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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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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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Reference Data for the Density and Viscosity of Liquid Aluminum and Liquid Iron J. Phys. Chem. Ref. Data 35, 285 (2006); http://dx.doi.org/10.1063/1.2149380 (16 pages) Online Publication Date: 10 February 2006
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The available experimental data for the density and viscosity of liquid aluminum and iron have been critically examined with the intention of establishing a density and a viscosity standard. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The proposed standard reference correlations for the density of the aluminum and iron are characterized by standard deviations of 0.65% and 0.77% at the 95% confidence level, respectively. The overall uncertainty in the absolute values of the density is estimated to be one of ±0.7% for aluminum and 0.8% for iron, which is worse than that of the most optimistic claims but recognizes the unexplained discrepancies between different methods. The standard reference correlations for the viscosity of aluminum and iron are characterized by standard deviations of 13.7% and 5.7% at the 95% confidence level, respectively. The uncertainty in the absolute values of the viscosity of the two metals is thought to be no larger than the scatter between measurements made with different techniques and so can be said to be ±14% in the case of aluminum and ±6% in the case of iron. © 2006 American Institute of Physics. |
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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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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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Evaluated Kinetic Data for Combustion Modeling: Supplement II J. Phys. Chem. Ref. Data 34, 757 (2005); http://dx.doi.org/10.1063/1.1748524 (641 pages) Online Publication Date: 27 July 2005
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This compilation updates and expands two previous evaluations of kinetic data on elementary, homogeneous, gas phase reactions of neutral species involved in combustion systems [J. Phys. Chem. Ref Data 21, 411 (1992); 23, 847 (1994)]. The work has been carried out under the auspices of the IUPAC Commission on Chemical Kinetics and the UK Engineering and Physical Sciences Research Council. Individual data sheets are presented for most reactions but the kinetic data for reactions of C2, C, ethyl, i-propyl, t-butyl, and allyl radicals are summarized in tables. Each data sheet sets out relevant thermodynamic data, experimental kinetic data, references, recommended rate parameters with their error limits and a brief discussion of the reasons for their selection. Where appropriate the data are displayed on an Arrhenius diagram or by fall-off curves. Tables summarizing the recommended rate data and the thermodynamic data for the reactant and product species are given, and their sources referenced. As in the previous evaluations the reactions considered relate largely to the combustion in air of organic compounds containing up to three carbon atoms and simple aromatic compounds. Thus the data base has been expanded, largely by dealing with a substantial number of extra reactions within these general areas. © 2005 American Institute of Physics. |
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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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Announcement: Farewell to Co-Editor Malcolm W. Chase, Jr. J. Phys. Chem. Ref. Data 37, 1 (2008); http://dx.doi.org/10.1063/1.2816952 (1 page) Online Publication Date: 2 January 2008
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J. Phys. Chem. Ref. Data 29, 167 (2000); http://dx.doi.org/10.1063/1.556058 (100 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); 28, 191 (1999)]. The present evaluation is limited to the inorganic halogen 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 102 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 that 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. © 2000 American Institute of Physics and American Chemical Society. |
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Cross Sections for Electron Collisions with Hydrogen Molecules J. Phys. Chem. Ref. Data 37, 913 (2008); http://dx.doi.org/10.1063/1.2838023 (19 pages) Online Publication Date: 31 March 2008
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Cross section data have been compiled for electron collisions with hydrogen molecules based on 71 references. Cross sections are collected and reviewed for total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, dissociation, ionization, emission of radiation, and dissociative attachment. For each process, the recommended values of the cross section are presented for use. The literature has been surveyed through the end of 2006.
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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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J. Phys. Chem. Ref. Data 33, 1005 (2004); http://dx.doi.org/10.1063/1.1691451 (7 pages) Online Publication Date: 28 October 2004
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A simple extended corresponding-states principle is used to represent the vapor pressure of ammonia and trideuteroammonia from the triple point to critical point and to describe the available experimental data along with extrapolation beyond their ranges of available experimental data. This work takes advantage of the adoption of the ITS-90 temperature scale and of the new critical parameters obtained from the extended corresponding-states principle. The vapor pressure data are described within their scatter in the entire temperature range. Comparisons with the available data show that the extended corresponding-states principle may calculate the vapor-pressure values within 0.05%–0.1% The substance-dependent characteristic parameters are given, such as critical temperature, critical density, critical pressure, acentric factor, and aspherical factor. The values of the pressures, along with their first and second derivatives as a function of temperature over the entire region from the triple point to the critical point are tabulated and recommended for scientific and practical uses. © 2004 American Institute of Physics. |
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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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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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J. Phys. Chem. Ref. Data 37, 7 (2008); http://dx.doi.org/10.1063/1.2789451 (90 pages) Online Publication Date: 23 January 2008
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Energy levels, with classifications and uncertainties, have been compiled for the spectra of the neutral atom and all positive ions of potassium (Z = 19). Wavelengths with classifications, intensities, and transition probabilities are also tabulated. In addition, ground states and ionization energies are listed. For many ionization stages experimental data are available; however for those for which only theoretical calculations or fitted values exist, these are reported.
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J. Phys. Chem. Ref. Data 29, 1 (2000); http://dx.doi.org/10.1063/1.556054 (39 pages)
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A correlation for estimating the vapor pressure of normal alkanes from methane through n-hexatriacontane and isomers of butane to nonane is reported. This work extends the correlation for normal alkanes (CnH2n+2), with n ⩽ 20, reported by Ambrose, to both normal alkanes with n ⩽ 36 and their isomers with n ⩽ 9. This vapor pressure equation was based on the Wagner equation and is similar to that used by Ambrose. Literature vapor pressure measurements have been reviewed. Tables are given that list the type of apparatus, measurement range and precision, and chemical purity. These criteria were initially used to select measurements for inclusion in the regression analyses to determine the coefficients of the correlation. Vapor pressures estimated from the correlation were compared with all vapor pressure (p1+g) measurements reviewed in this work. At pressures greater than 1 kPa, the vapor pressure equation presented here has the following accuracies: 0.0001⋅p1+g for methane, 0.001⋅p1+g for ethane, propane, and n-butane, 0.002⋅p1+g for n-pentane through n-octane, 2-methylpropane, and 2-methylbutane, 0.005⋅p1+g for 2,2-dimethylpropane, n-nonane, n-decane, and the isomers of hexane through nonane, 0.01⋅p1+g for n-undecane to n-hexadecane, 0.02⋅p1+g for n-heptadecane to n-eicosane, 0.05⋅p1+g for n-heneicosane to n-octacosane, and 0.10⋅p1+g for n-nonacosane to n-hexatriacontane. Equations for the critical temperatures and pressures of the normal alkanes as functions of the carbon number are also reported. © 2000 American Institute of Physics. |
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Atomic Transition Probabilities of Aluminum. A Critical Compilation J. Phys. Chem. Ref. Data 37, 709 (2008); http://dx.doi.org/10.1063/1.2734564 (203 pages) Online Publication Date: 6 March 2008
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This compilation is the second in a series of updates to Atomic Transition Probabilities, Sodium through Calcium, published in 1969 by
Wiese et al. [Atomic Transition Probabilities, Vol. II, Vol. II: Sodium through Calcium, NSROS-NBS Vol. 2 (U.S. GPO, Washington, D.C., 1969)]
. Atomic transition probabilities have been critically evaluated and compiled for about 5000 spectral lines of aluminum (nuclear charge Z = 13). The cited values and their estimated uncertainties are based on our consideration of all available theoretical and experimental literature sources. All ionization stages (except for hydrogenic) are covered, and the data are presented in separate tables for each atom and ion. Separate listings are given for “allowed” (electric dipole) and “forbidden” (magnetic dipole plus electric and magnetic quadrupole) transitions. In each spectrum, lines are grouped into multiplets which are arranged in order of ascending lower- and upper-level energies, respectively. For each line, the emission transition probability Aki, the line strength S, and (for allowed lines) the absorption oscillator strength fik are given, together with the spectroscopic designation, the wavelength, the statistical weights, and the energy levels of the lower and upper states. The estimated relative uncertainties of the line strength are also indicated, as are the source citations. We include only those lines whose transition rates are deemed sufficiently accurate to qualify as reference values. Short introductions precede the tables for each ion.
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Editorial: Greetings from the New Co-Editors J. Phys. Chem. Ref. Data 37, 5 (2008); http://dx.doi.org/10.1063/1.2827989 (1 page) Online Publication Date: 2 January 2008
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IUPAC Critical Evaluation of Thermochemical Properties of Selected Radicals. Part I J. Phys. Chem. Ref. Data 34, 573 (2005); http://dx.doi.org/10.1063/1.1724828 (84 pages) Online Publication Date: 27 May 2005
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This is the first part of a series of articles reporting critically evaluated thermochemical properties of selected free radicals. The present article contains datasheets for 11 radicals: CH, CH2(triplet), CH2(singlet), CH3, CH2OH, CH3O, CH3CO, C2H5O, C6H5CH2, OH, and NH2. The thermochemical properties discussed are the enthalpy of formation, as well as the heat capacity, integrated heat capacity, and entropy of the radicals. One distinguishing feature of the present evaluation is the systematic utilization of available kinetic, spectroscopic and ion thermochemical data as well as high-level theoretical results. © 2005 American Institute of Physics. |
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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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