Surface tension values for 94 liquids whose molecules include cyclic structures have been compiled from databases, books, and papers in the literature for different temperatures. These values were screened, and for each fluid the number of selected data ranges from 9 to 195, yielding a total of 2389 data points, of which 560 correspond to experimental ones. Recommended temperature-dependent correlations are proposed for 92 of the 94 substances considered, as the selected datasets for the remaining two exhibit significant discrepancies. The Guggenheim–Katayama analytical expression was applied using two or four adjustable coefficients, except for methylcyclopropane, for which six were required. The proposed correlations yield mean absolute deviations below 0.4 mN/m and mean absolute percentage deviations below 1.7%, except for 4-methylcyclopentene and 1-ethyltetralin, for which values around 2.3% were obtained. Moreover, percentage deviations below 9.1% are found for almost all selected data, with the only exceptions being two values for cyclopentane and one for 1-ethyltetralin, for which two different data sources provide different values at the highest temperatures. In general, the largest deviations are due to this kind of disagreement rather than to poor fitting by the correlation model. These new correlations expand the existing collection, which includes common substances, alcohols, refrigerants, organic acids, n-alkanes, esters, ethers, and alkenes, by incorporating 25 alkylcyclohexanes, 15 alkylcyclopentanes, 14 cycloaliphatic alcohols, 7 cycloalkanes, 13 cycloalkenes, 12 cyclobenzenes, and 6 multiring cycloalkanes, classified according to DIPPR nomenclature.
Electron ionization (EI) induced decomposition pathways are determined for various steroids representing skeletons of estrane, androstane, pregnane, cholane, cholestane, stigmastane and more. Diagnostic ions are identified and recommended for decoding selected structural elements to reconstruct the structure of an unknown. The striking dependencies of the sites of charge localization and bond fissions on the number and the location of hydroxyl, carbonyl, carboxyl, and amine functionalities in the steroid backbone are highlighted to assist in a reliable structure elucidation of unknowns. The controlling status of stereochemistry in EI-induced decomposition of steroids is considered. The potential and limitations of EI mass spectrometry in the structure determination of steroids are emphasized.
High-precision ro-vibrational spectroscopy of carbon dioxide isotopologues is essential for atmospheric remote sensing, climate studies, and fundamental molecular physics. Accurate determination of CO2 vibrational-rotational energy levels is crucial for improving the reliability of relevant spectroscopic databases. We report a cavity-enhanced double-resonance spectroscopy technique stabilized by an optical frequency comb for precision measurement of weak rovibrational transitions in CO2 isotopologues. By pumping a strong transition while probing a weak counterpart, the method enables sub-Doppler detection of 18 weak transitions in the 41 101-00 001 band with uncertainties of 4-52 kHz. Using complementary rovibrational models, we derived 394 and 133 experimental energy levels for (CO2)-C-12-O-16 and (CO2)-C-13-O-16, respectively, up to 14 170 cm(-1). These results, all from sub-Doppler measurements, provide significantly more accurate benchmarks than current spectroscopic databases and will improve atmospheric remote-sensing retrievals for climate and planetary science. The approach is generally applicable to other polyatomic molecules and opens a route to systematic precision spectroscopy of weak and forbidden transitions.
Electron collision cross section data are compiled from the literature for electron collisions with the oxygen molecule O-2 and the atom O. Cross sections are collected and reviewed for total scattering, elastic scattering, momentum transfer, rotational excitation, vibrational excitation, electronic excitation, dissociative processes, and ionization. The literature has been surveyed up to the end of 2024. For each of these processes, the recommended values of the cross sections are presented with an estimated uncertainty.
The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) methods are used to provide excitation energies, radiative transition data, lifetimes, Landeg-factors, hyperfine interaction constants and isotope shift parameters for the 99 lowest levels of configurations 1s (2)2snl (n <= 7) + 1s (2)2p (2) in beryllium. Compared with available experimental excitation energies, the average difference with the standard deviation is 7.08 +/- 1.14 cm(-1) (0.011% +/- 0.003%), which demonstrates the excellent theory-observation agreement. The uncertainties of the transition rates are estimated based on two independent methods. The present MCDHF/RCI oscillator strengths and those obtained from the explicitly correlated Gaussian method all agree within 2%, except for four transitions affected by strong cancellation effects. For lifetimes, hyperfine splittings and isotope shifts, the present MCDHF/RCI results show good agreement with the few available experimental values, supporting the reliability of our predictions for many states lacking experimental measurements. These comprehensive results can be used in line identification and diagnostics of astrophysical plasmas.
Relative density measurements of International Association for the Physical Sciences of the Oceans (IAPSO) Standard Seawater (P161, Sp = 34.995) were carried out with the recently developed dual-capillary method. Isobaric measurements were performed from 298.15 K down to the supercooled liquid region, similar to 8-13 K below the equilibrium freezing line, at pressures from atmospheric up to 110 MPa. Densities relative to the density at the reference temperature of 293.15 K are presented together with derived thermal expansion coefficients for individual isobars. Expanded uncertainties (k = 2) of the relative densities range from 0.000 020 to 0.000 031. A particular advantage of the present approach is that the thermal expansion coefficients close to the equilibrium freezing line are based on measurements from both of its sides-in the stable and metastable regions. Besides the dual-capillary data, results of complementary density measurements with IAPSO Standard Seawater using a vibrating tube densimeter (VTD) from 275.15 to 343.15 K at ambient pressure are presented. The dual-capillary and VTD results are compared with the Thermodynamic Equation of Seawater 2010 (TEOS-10). The new data agree with TEOS-10 within its expanded uncertainties from 273.15 to 313.15 K and they deviate significantly outside this temperature range. A simple correlation based on scaling the equation of state for supercooled ordinary water was developed to represent standard seawater densities in the studied region. The correlation represents measured densities within 10 ppm up to 70 MPa and within 25 ppm up to 110 MPa.
An “isochoric” model is presented for calculating the standard (i.e., at infinite dilution in water) thermodynamic properties of ions at temperatures from 373 to 2000 K and pressures corresponding to water densities from about 250 to 1500 kg m−3. The main correlation variable is the standard partial isochoric heat capacity of an ion/electrolyte Cv,2o, which depends weakly on temperature and is virtually independent of the pressure/density of water at T > 373 K. Data supporting the main assumptions of the model are presented. The combination of Cv,2o with the existing method for calculating standard partial volumes of the ion/electrolyte at T > 373 K allows calculating the increments of the standard partial Gibbs energies G2o, enthalpies H2o, entropies S2o, and isobaric heat capacities Cp,2o from the reference point at 373.15 K and 300 MPa up to 2000 K and 10 GPa. The analysis of experimental data for NaCl, NaOH, and HCl allowed choosing the optimal type of analytical expressions for the “isochoric” model. The best studied at high T and P water ionization constant was chosen as a test. At the saturated water vapor pressure, the agreement between the precise experimental and calculated values of water ionization constants pKw is excellent. Over the entire T–P range of data availability (up to 1273 K and up to a water density of ∼1700 kg m−3), the agreement is at least satisfactory, and the quantity and quality of experimental pKw do not allow more definitive conclusions.
We present a thermodynamic model of speed of sound w in humid air as a function of the parameters of influence, namely temperature T, pressure p, relative humidity hr, carbon dioxide concentration xCO2, and acoustic frequency f. The validity of the model extends between 200 K and 647 K, for pressures up to 10 MPa. By implementing the most accurate thermodynamic information currently available for dry air, water vapor, and their interaction, including heat capacities, virial coefficients, and relaxation parameters, the model revises and updates the most complete previous correlation [A. J. Zuckerwar, Handbook of the Speed of Sound in Real Gases – Volume III Speed of Sound in Air (Academic Press, London, 2002)], reducing its relative standard uncertainty by more than one order of magnitude, down to 25 ppm at ordinary, near-ambient conditions. The software implementation of the model is made available by publication of source and executable files. To test the validity of the model and its practical application, we have measured the speed of sound in humid air near ambient pressure using an acoustic wavelength meter set up in a hemi-anechoic chamber and compared a subset of these experimental determinations with those obtained by flowing air, sampled from the same environment, through a spherical resonator. The results from both experiments were found consistent with the model within their combined uncertainties. The positive outcome of the comparison suggests that acoustic thermometry in humid air may be realized at the level of 0.015 K with perspectives for application to dimensional measurements, temperature and acoustic metrology, and atmospheric physics.
The densities of mixtures of ordinary water and O-18-enriched water have been measured all over the range of compositions at temperatures between 293.15 and 313.15 K. The molar volumes of the mixtures exhibit a linear dependence with composition over the studied temperature range, indicating that the mixtures behave as an ideal solution. The molar volume of pure (H2O)-O-18 has been obtained by extrapolation, accounting for the isotopic composition of the measured solutions, and the results are compared with those reported in the literature. The thermal expansion coefficient of pure (H2O)-O-18 was also calculated over the same temperature range and is similar to that reported for ordinary water. We found that the ratio of densities of (H2O)-O-18 and ordinary water is independent of temperature, which allows to estimate the density of (H2O)-O-18 over an extended range of temperatures. Published by AIP Publishing on behalf of the National Institute of Standards and Technology. https://doi.org/10.1063/5.0275687
A reference correlation for the viscosity of n-propyl alcohol was developed based on carefully selected primary experimental data. The correlation, formulated as a function of temperature and density, covers the temperature range from 153-618 K and pressures up to 118 MPa. Comparison between the correlation and the experimental data showed an average absolute relative deviation of 1.01% and a bias of -0.18% for the data under pressure, while the values of 0.75% and +0.01% were observed for data close to 0.1 MPa. The expanded uncertainty (with coverage factor k = 2) of the reference correlation in the liquid phase was estimated to be 2.0% close to 0.1 MPa and 2.5% under pressure. In the supercritical region, the expanded uncertainty (k = 2) was estimated to be 4.2%. The uncertainty was estimated doubled relative to the nearby region when no primary data exist. In the gaseous phase, the expanded uncertainty (k = 2) was estimated to be 2.2% above 373 K and 4.6% below 373 K. The uncertainty in the critical region may be larger because of the lack of experimental data. Additionally, an empirical equation valid from 153-363 K and at pressures of 0.1 MPa was proposed, with an estimated expanded uncertainty of 2.0% (k = 2).
Based on the direct summation technique, improved ideal-gas partition functions and related thermochemical quantities are reported for the parent isotopologues of molecular oxygen and water, O-16(2) and H-2 O-16, respectively. The new results update those of two previous publications reported in this journal [Furtenbacher et al., J. Phys. Chem. Ref. Data 45, 043104 (2016) and Furtenbacher et al., J. Phys. Chem. Ref. Data 48, 023101 (2019)]. The improved thermochemical functions, tabulated at 1 K intervals between 0 and 5000 K in the supplementary material to this paper, use (a) the exact values of the fundamental physical constants fixed in the 2019 redefinition of the International System of Units, (b) an improved set of empirical energy levels for H-2 O-16, with much improved uncertainties at low rovibrational excitations, (c) different approaches to the uncertainty budget, including correcting an error in previous uncertainty calculations for O-16(2), and (d) a small correction to the ideal-gas thermochemical functions of O-16(2), making them applicable for oxygen of natural isotopic composition, which is needed for the development of practical thermodynamic models.
Surface tension values for 42 alkenes at different temperatures have been compiled from databases, books, and papers in the literature. Those values have been screened, and finally 1266 data were selected. For each fluid, the Guggenheim-Katayama analytical expression was used with two or four adjustable coefficients, except for 1-octene, for which six were needed. As the main result, recommended correlations as a function of temperature are proposed for the 42 alkenes. The proposed correlations provide mean absolute deviations below 0.55 mN/m and mean absolute percentage deviations below 2.7%. Moreover, percentage deviations less than or equal to 8.1% are obtained for almost all the selected data, with the only exceptions being sets of few data for 1,4-pentadiene and dicyclopentadiene, for which there are at least two different sources of data providing different values. In general, the highest deviations are due to this kind of disagreement and not to the poor fitting performance of the correlation model. These new correlations expand the existing collection, including common substances, alcohols, refrigerants, organic acids, n-alkanes, esters, and ethers.
The free-jet millimeter wave absorption spectrum of pyrrole has been measured in the 59.6-78.3 GHz frequency range. The rotational spectra of four species have been assigned: the one for the normal species in both the vibrational ground state and the first excited state of the NH out-of-plane bending and those of two 13C monosubstituted isotopologues observed in natural abundance. For each species, the hyperfine structure due to the nuclear quadrupole coupling interaction of the 14N nucleus with the overall rotation has been resolved. The new rotational data for the ground state and the vibrational satellite were analyzed simultaneously with existing microwave/millimeter-wave data and rovibrational data for the fundamental [nu = 474.647 552(5) cm-1], first overtone [nu = 962.720 890(5) cm-1], and first hot bands of the NH out-of-plane bending motion. A comprehensive list of lines and the resulting set of spectroscopic parameters are provided.
Five far infrared absorption spectra of water vapor highly enriched in 17O, 18O and deuterium (D) are analyzed. The Fourier transform spectra at room temperature were recorded at the SOLEIL synchrotron facility with a 151.75 m absorption pathlength. The 50–720 cm−1 studied spectral region corresponds to the rotational band. The combined line list of the five spectra counts more than 12 900 lines which were assigned to about 13 960 transitions of the nine stable water isotopologues (H2XO, HDXO, D2XO with X = 16, 17, and 18). Line centers are determined with a typical accuracy of 5 × 10−5 cm−1 for isolated lines. The strong isotopic enrichment combined with the large spectral coverage and the unprecedented sensitivity of the recordings allow for extending considerably previous literature data for the HD17O and HD18O minor isotopologues. For each of these two species, the set of transition frequencies is merged to literature sources to generate extensive sets of accurate empirical rotational-vibrational energies for the ground, (000), and first excited, (010), vibrational states. The comparison to the previous datasets from an International Union of Pure and Applied Chemistry task group illustrates a gain on the average energy accuracy by more than one order of magnitude. Based on these accurate energy levels, recommended lists of transitions are generated with a 10−25 cm/molecule intensity cut-off for the (000)–(000), and (010)–(010) rotational bands and the ν2 band for both HD17O and HD18O. For the microwave region (0–1.5 THz), more complete lists with an intensity cut-off lowered to 10−29 cm/molecule are provided.
We have constructed an effective Hamiltonian model for the rotational–vibrational states of molecular carbon dioxide. The model is constrained by a large amount of spectroscopic data for frequencies of rovibrational transitions. From this formulation, we construct partition functions and derive thermochemical quantities (enthalpy, entropy, heat capacity) for the 12 stable isotopologues of the CO2 molecule. These are combined to produce thermochemical functions for CO2 of natural isotopic abundance. The resulting ideal-gas heat capacities, which will serve as input for a future reference equation of state, differ from previous, simpler calculations by amounts that are not large but that significantly exceed the uncertainty of the present calculations.
While there is a significant body of literature pertaining to thermophysical property measurements of molten salts, there is often a wide degree of variability among independent measurements of the same compounds. As such, the scientific community benefits greatly from an unbiased, independent assessment of duplicate datasets, so that reference correlations which describe these thermophysical properties as functions of temperature can be determined and then commonly used by researchers, scientists, and engineers. With regard to molten fluoride compounds, a significant time has elapsed since density and viscosity reference correlations have been determined; Janz conducted the most recent effort, in 1988, to provide reference correlations for the densities and viscosities of molten fluoride compounds via the National Standard Reference Data System coordinated by the National Bureau of Standards. Since then, new data have been published for molten fluoride compounds, and a new precedent has surfaced for putting forth reference correlations that involve fitting to multiple primary datasets. In this work, reference correlations are put forth for molten alkali and alkaline earth fluoride compounds in an effort to provide updated, improved correlations for general use. For molten alkali fluoride densities, estimated uncertainties with a 95% confidence interval are summarized as follows: LiF (0.63%), NaF (0.48%), KF (0.76%), RbF (0.93%), and CsF (0.75%). For molten alkaline earth fluoride densities, an estimated uncertainty was not able to be quantified for BeF2 because of limited data; however, estimated uncertainties with a 95% confidence interval are summarized as follows for the remaining alkaline earth fluorides: MgF2 (1.5%), CaF2 (0.92%), SrF2 (1.6%), and BaF2 (0.23%). For molten alkali fluoride viscosities, uncertainty was not able to be quantified for RbF and CsF because of limited data; however, estimated uncertainties with a 95% confidence interval are summarized as follows for the remaining alkali fluorides: LiF (4.4%), NaF (3.0%), and KF (4.0%). For molten alkaline earth fluoride viscosities, limited consistent data resulted in the recommendation of single datasets (from literature) that are deemed to be the most trustworthy based on the quality of the underlying experimental studies.
Recommended values are given for the difference between the thermodynamic temperature T and T90, the temperature on the International Temperature Scale of 1990, for temperatures below 4.2 K. The recommendations are based on a combination of primary thermometry and thermodynamic calculations. Functions for both the difference T − T90 and its uncertainty are provided.
Measurement of sublimation enthalpies, especially for low-volatility compounds, is challenging using traditional calorimetric methods, as well as indirect methods via the Clapeyron equation. To ensure consistency across laboratories, the International Confederation for Thermal Analysis and Calorimetry Working Group Thermochemistry established several reference materials in 1999. This work extends previous research by providing reliable sublimation pressures and enthalpies for biphenyl and trans-stilbene, proposed in 1999 as tertiary reference materials. Using STAT8 and STAT9 apparatuses, experiments were conducted to measure the sublimation and saturated liquid pressures for biphenyl (286–363 K) and trans-stilbene (323–433 K). These new data on vapor pressure were supplemented by ideal-gas heat capacities calculated by combining statistical thermodynamics and density functional theory calculations and heat capacity measurements using Tian–Calvet calorimetry. Calculated ideal-gas heat capacities and critically assessed experimental data on sublimation/saturated liquid pressure, condensed-phase heat capacities, fusion properties, and sublimation enthalpies were subsequently treated simultaneously to obtain a consistent description of the sublimation and vaporization thermodynamic properties. The results show that biphenyl and trans-stilbene meet the criteria for becoming primary reference materials for sublimation pressures and enthalpies.
Key ions for structure elucidation in the electron ionization mass spectra of di- and polyfunctional compounds containing only a single functional group, such as hydroxyl, mercapto-, carbonyl, carboxyl, and amino functionality are revealed. They are attached to aliphatic, alicyclic, aromatic hydrocarbons and their hetero analogs. The analysis is extended to the spectra of polyfunctional compounds encompassing different functional groups including sugars, hydroxy acids, keto acids and amino acids. The potential of mass spectrometry for structure elucidation via chemical modification of these compounds is revealed as well. Diagnostic ions in the mass spectra of alkyl, trimethylsilyl, acetyl, trifluoroacetyl and methoxycarbonyl derivatives are identified.
Based on the direct summation technique, improved ideal-gas partition functions and related thermochemical quantities are reported for the parent isotopologues of molecular oxygen and water, 16O2 and H216O, respectively. The new results update those of two previous publications reported in this journal [Furtenbacher et al., J. Phys. Chem. Ref. Data 45, 043104 (2016) and Furtenbacher et al., J. Phys. Chem. Ref. Data 48, 023101 (2019)]. The improved thermochemical functions, tabulated at 1 K intervals between 0 and 5000 K in the supplementary material to this paper, use (a) the exact values of the fundamental physical constants fixed in the 2019 redefinition of the International System of Units, (b) an improved set of empirical energy levels for H216O, with much improved uncertainties at low rovibrational excitations, (c) different approaches to the uncertainty budget, including correcting an error in previous uncertainty calculations for 16O2, and (d) a small correction to the ideal-gas thermochemical functions of 16O2, making them applicable for oxygen of natural isotopic composition, which is needed for the development of practical thermodynamic models.
