Showing papers in "Journal of Physical and Chemical Reference Data in 2020"

Effective Attenuation Lengths for Different Quantitative Applications of X-ray Photoelectron Spectroscopy

Abstract: The effective attenuation length (EAL) is a useful parameter in quantitative applications of x-ray photoelectron spectroscopy (XPS). This parameter is used in place of the inelastic mean free path (IMFP) in expressions for different XPS applications to correct those expressions for elastic scattering of the photoelectrons. We consider expressions used to determine (i) the thickness of an overlayer film on a planar substrate, (ii) the surface composition, (iii) the depth of a thin marker or delta layer, and (iv) the shell thickness of a core–shell nanoparticle. An EAL can be used for each of these applications. In general, the EAL depends on the particular defining equation as well as on the XPS configuration. Many attempts were made in the 1970s and 1980s to measure EALs for the determination of overlayer-film thicknesses, but there were often wide scatters in the reported results due to the difficulty in preparing uniform films with known thicknesses. We have therefore been motivated to calculate EALs for each application. The SRD 82 database from the National Institute of Standards and Technology (NIST) provides EALs for the measurement of overlayer-film thicknesses and of marker-layer depths. These EALs can be determined for photoelectron energies between 50 eV and 2 keV and for user-specified XPS configurations. We review EAL predictive equations for the determination of overlayer-film thicknesses on a planar substrate for XPS with unpolarized x rays and with linearly polarized x rays as well as an EAL predictive equation for quantitative analysis by XPS. These equations are simple analytical expressions that are valid for well-defined ranges of experimental conditions and for useful ranges of electron energies. We also point out that EALs for the determination of overlayer-film thicknesses can be derived from the simulated photoelectron intensities obtained from the NIST Database for the Simulation of Electron Spectra for Surface Analysis (SRD 100). Where possible, we make comparisons of the calculated EALs with illustrative experimental results. A key parameter in the EAL predictive equations is the so-called albedo, a useful measure of the strength of elastic-scattering effects in a material. The albedo is a simple function of the IMFP and the transport mean free path (TRMFP). We provide a tabulation of albedo and TRMFP values in the supplementary material for 41 elemental solids and 42 inorganic compounds for photoelectron energies between 50 eV and 30 keV. For other materials, albedo values can be determined from IMFP and TRMFP data available in the NIST SRD 82 and SRD 100 databases.

The W2020 Database of Validated Rovibrational Experimental Transitions and Empirical Energy Levels of Water Isotopologues. II. H217O and H218O with an Update to H216O

Abstract: The W2020 database of validated experimental transitions and accurate empirical energy levels of water isotopologues, introduced in the work of Furtenbacher et al. [J. Phys. Chem. Ref. Data 49, 033101 (2020)], is updated for H216O and newly populated with data for H217O and H218O. The H217O/H218O spectroscopic data utilized in this study are collected from 65/87 sources, with the sources arranged into 76/99 segments, and the data in these segments yield 27 045/66 166 (mostly measured) rovibrational transitions and 5278/6865 empirical energy levels with appropriate uncertainties. Treatment and validation of the collated transitions of H216O, H217O, and H218O utilized the latest, XML-based version of the MARVEL (Measured Active Rotational-Vibrational Energy Levels) protocol and code, called xMARVEL. The empirical rovibrational energy levels of H217O and H218O form a complete set through 3204 cm−1 and 4031 cm−1, respectively. Vibrational band origins are reported for 37 and 52 states of H217O and H218O, respectively. The spectroscopic data of this study extend and improve the data collated by an International Union of Pure and Applied Chemistry Task Group in 2010 [J. Tennyson et al., J. Quant. Spectrosc. Radiat. Transfer 110, 2160 (2010)] as well as those reported in the HITRAN2016 information system. Following a minor but significant update to the W2020-H216O dataset, the joint analysis of the rovibrational levels for the series H216O, H217O, and H218O facilitated development of a consistent set of labels among these three water isotopologues and the provision of accurate predictions of yet to be observed energy levels for the minor isotopologues using the combination of xMARVEL results and accurate variational nuclear-motion calculations. To this end, 9925/8409 pseudo-experimental levels have been derived for H217O/H218O, significantly improving the coverage of accurate lines for these two minor water isotopologues up to the visible region. The W2020 database now contains almost all of the transitions, apart from those of HD16O, required for a successful spectroscopic modeling of atmospheric water vapor.

W2020: A Database of Validated Rovibrational Experimental Transitions and Empirical Energy Levels of H216O

Abstract: A detailed understanding of the complex rotation–vibration spectrum of the water molecule is vital for many areas of scientific and human activity, and thus, it is well studied in a number of spectral regions. To enhance our perception of the spectrum of the parent water isotopologue, H216O, a dataset of 270 745 non-redundant measured transitions is assembled, analyzed, and validated, yielding 19 204 rovibrational energy levels with statistically reliable uncertainties. The present study extends considerably an analysis of the rovibrational spectrum of H216O, published in 2013, by employing an improved methodology, considering about one-third more new observations (often with greatly decreased uncertainties), and using a highly accurate first-principles energy list for validation purposes. The database of experimental rovibrational transitions and empirical energy levels of H216O created during this study is called W2020. Some of the new transitions in W2020 allow the improved treatment of many parts of the dataset, especially considering the uncertainties of the experimental line positions and the empirical energy values. The W2020 dataset is examined to assess where measurements are still lacking even for this most thoroughly studied isotopologue of water, and to provide definitive energies for the lower and upper states of many yet-to-be-measured transitions. The W2020 dataset allows the evaluation of several previous compilations of spectroscopic data of water and the accuracy of previous effective Hamiltonian fits.

Equations of State for the Thermodynamic Properties of Binary Mixtures for Helium-4, Neon, and Argon

Abstract: Based on the conceptual design reports for the Future Circular Collider cryogenic system, the need for more accurate thermodynamic property models of cryogenic mixtures of noble gases was identified. Both academic institutes and industries have identified the lack of a reliable equation of state for mixtures used at very low temperatures. Detailed cryogenic architecture modeling and design cannot be carried out without accurate fluid properties. Therefore, the helium–neon equation was the first goal of this work, and it was further extended to other fluids beneficial for scientific and industrial applications beyond the particle physics needs. The properties of the noble gas mixtures of helium–neon, neon–argon, and helium–argon are accurately modeled with the equations of state explicit in the Helmholtz energy.

Thermophysical Properties of 1-Hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][(CF3SO2)2N]—New Data, Reference Data, and Reference Correlations

Abstract: Published data on the thermophysical properties of ionic liquids are normally in disagreement if results from different laboratories, using different samples and different measurement protocols, are compared. This fact was recognized years ago at the level of the International Union of Pure and Applied Chemistry (IUPAC), which established IUPAC Project 2002-005-1-100 (Thermodynamics of ionic liquids, ionic liquid mixtures, and the development of standardized systems), with the main objective of recommending a reference ionic liquid, making reference-quality measurements on selected thermophysical properties of both the pure ionic liquid and its mixtures, establishing recommended values for the properties measured, and providing recommendations on measurement methods. The ionic liquid chosen was 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][(CF3SO2)2N], because of its stability, low viscosity compared with that of most common ionic liquids, low water solubility, ease of preparation and purification, and commercial availability. Due to its hydrophobicity, it is capable of being obtained very pure, with water amounts as small as 20 ppm. This paper reports new results obtained with the sample of [C6mim][(CF3SO2)2N] synthesized in the IUPAC project, namely on density, speed of sound, surface tension, and refractive index, as well as thermal conductivity of a commercial sample at P = 0.1 MPa, as a function of temperature, and proposes reference data and reference data correlations for the density, speed of sound, heat capacity, surface tension, viscosity, electrical conductivity, thermal conductivity, refractive index, ion self-diffusion coefficient, and melting temperature of this ionic liquid at 0.1 MPa, as a function of temperature, using these and other data reported up to July 2020. Rheological measurements demonstrated that this ionic liquid is Newtonian.

An Organized Collection of Theoretical Gas-Phase Geometric, Spectroscopic, and Thermochemical Data of Oxygenated Hydrocarbons, CxHyOz (x, y = 1, 2; z = 1–8), of Relevance to Atmospheric, Astrochemical, and Combustion Sciences

Abstract: The objective of this work is to present a unified collection of structural and chemical information on a series of neutral chemical tri-elemental species up to a molecular formula C2H2O8, which may be used for validation purposes, for deep structured learning or indeed more simply for basic data of a single species. Such a collection vastly is tightly focused in terms of its component parts, contains novel results, and covers a number of chemical classes including stable molecules, radicals, carbenes, dipolar species, and excited states. Wherever possible, comparisons are made to the experimental and quantum chemical literature of gas-phase molecules, but the paucity of such means that there is only a very limited scope for validation. The primary data consist of structural information in the form of Cartesian coordinates, rotational constants together with vibrational frequencies, and anharmonicity coefficients, all obtained through density functional, B3LYP, calculations with the cc-pVTZ+d basis set. Standard statistical thermodynamic relations are then used to compute entropy, specific heat at constant pressure, and an enthalpy function over temperatures from 298.15 K to 2000 K. Supplementary material contains all the information necessary to carry out these calculations over different conditions as required as well as the raw species data. High-level quantum mechanical computations employing composite model chemistries, including CBS-QB3, CBS-APNO, G3, G4, W1BD, WMS, W2X, and W3X-L, are used to derive formation enthalpies via atomization and/or isodesmic calculations as appropriate.

Integral Cross Sections for Electron-Zinc Scattering over a Broad Energy Range (0.01-5000 eV)

Abstract: We report results from the application of our optical potential and relativistic optical potential methods to electron–zinc scattering. The energy range of this study was 0.01–5000 eV, with original results for the summed discrete electronic-state integral excitation cross sections and total ionization cross sections being presented here. When combined with our earlier elastic scattering data [Marinkovic et al., Phys. Rev. A 99, 062702 (2019)], and the quite limited experimental and theoretical results for those processes from other groups, we critically assemble a recommended integral cross section database for electron–zinc scattering. Electron transport coefficients are subsequently calculated for reduced electric fields ranging from 0.1 to 1000 Td, using a multiterm solution of Boltzmann’s equation. Some differences with corresponding results from the earlier study of White et al. [J. Phys. D: Appl. Phys. 37, 3185 (2004)] were noted, indicating in part the necessity of having accurate and complete cross section data, over a wide energy regime, when undertaking such transport simulations.

Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based on Ab Initio Calculations and Viscosity Ratio Measurements

Abstract: The combined use of experimental viscosity ratios together with ab initio calculations for helium has driven significant improvements in the description of dilute gas transport properties. Here, we first use improvements made to ab initio helium calculations to update viscosity ratios measured for H2, Ar, CH4, and Xe by May et al. [Int. J. Thermophys. 28, 1085 (2007)] over the temperature range of 200–400 K, reducing the uncertainties of the data to 0.055%, 0.038%, 0.067%, and 0.084%, respectively. Separately, we extend the technique of combining viscosity ratios with ab initio calculations to develop new reference correlations for the dilute gas viscosity of 10 gases: helium, neon, argon, krypton, xenon, hydrogen, nitrogen, methane, ethane, and propane. This is achieved by combining the ratios of viscosities calculated ab initio at the target temperature and at 298.15 K with experimentally based reference viscosity values for each gas at 298.15 K. The new reference dilute gas viscosity correlations span temperature ranges from at least 150 K to 1200 K with relative uncertainties between 30% (krypton) and 85% (methane) lower than the original ab initio results. For the noble gases, ab initio calculations for the Prandtl number are used to develop reference correlations for thermal conductivity ranging from at least 100 K to 5000 K, with relative uncertainties ranging from 0.04% (argon) to 0.20% (xenon). The new reference correlations are compared with available experimental data at dilute gas conditions. In general, the data agree with the new correlations within the claimed experimental uncertainty.

The Ionization Constant of Water at Elevated Temperatures and Pressures: New Data from Direct Conductivity Measurements and Revised Formulations from T = 273 K to 674 K and p = 0.1 MPa to 31 MPa

Abstract: Experimental values for the ionization constant of water, pKw,m, from T = 373 K to T = 674 K and from p = 5.75 MPa to p = 31.15 MPa, have been derived from direct measurements of the electrical conductivity of very pure water at the University of Guelph, the University of Delaware, and the Oak Ridge National Laboratory using high-precision high-temperature flow-through AC electrical conductance instruments based on the design by Wood and co-workers [J. Phys. Chem. 99, 11612 (1995)]. The results compare well with published high-temperature potentiometric and calorimetric studies up to 573 K and are consistent with the 1981 and 2006 IAPWS (International Association for the Properties of Water and Steam) pKw,m formulations to within better than 0.1 pK units up to 598 K and to better than 0.2 pK units at 623 K. Above 623 K, the 2006 and 1981 IAPWS formulations showed systematic deviations from the new results, which reached two and five orders of magnitude near the critical point, respectively. Based on these conductivity studies and critically evaluated literature data, revised parameters for the Marshall–Franck and Bandura–Lvov equations of state are reported, which reproduce the experimental data with standard uncertainties u(pK) = 0.018 and u(pK) = 0.016, respectively, over the experimental temperature range at water densities from 1.00 g cm−3 to 0.20 g cm−3, which corresponds to T = 373 K–674 K from psat to p = 31 MPa, and over the range T = 273 K–373 K at p = 100 kPa. These new experimental conductivity results are the most accurate values to be reported under near-critical conditions for densities between 0.50 g cm−3 and 0.20 g cm−3.

Recommended Values for the Viscosity in the Limit of Zero Density and its Initial Density Dependence for Twelve Gases and Vapors: Revisited from Experiment between 297 K and 691 K

Abstract: Previously published experimental viscosity data at low density, originally obtained using all-quartz oscillating-disk viscometers for 12 gases and vapors in the temperature range between 297 K and 691 K, were re-evaluated after an improved re-calibration. The relative combined expanded (k = 2) uncertainty of the re-evaluated data is 0.2% near room temperature and increases to 0.3% at higher temperatures. The re-evaluated data for sulfur hexafluoride, methanol, n-pentane, n-hexane, n-heptane, neopentane, cyclohexane, benzene, toluene, p-xylene, phenol, and triethylamine were arranged in approximately isothermal groups and converted into quasi-isothermal viscosity data using a first-order Taylor series in temperature. Then, they were evaluated by means of a series expansion truncated at first order to obtain the zero-density and initial density viscosity coefficients, η(0) and η(1). When the number of isothermal data or their quality was not adequate, the Rainwater–Friend theory for the initial density dependence of the viscosity was additionally used to derive η(0) and η(1) values. Finally, reliable η(0) and η(1) values, preferably obtained from the isotherms, were recommended as reference values for the 12 gases and vapors in the measured temperature range to be applied when generating any new viscosity formulation.