Volume 29, Issue 3, May 2000
Index of content:
29(2000); http://dx.doi.org/10.1063/1.1288407View Description Hide Description
Sulfur hexafluoride is commonly used as a gaseous dielectric and as a plasma etching gas. In this work, the state of knowledge on electron-interaction cross sections and electron-swarm parameters in is comprehensively reviewed and critically assessed. Cross sections are presented and discussed for the following scattering processes: total electron scattering; differential elastic;elastic integral; elastic momentum; total vibrational; total and partial ionization; total dissociative and nondissociative electron attachment; and dissociation into neutrals. Coefficients for electron-impact ionization, effective ionization, electron attachment, electron drift, and electron diffusion are also reviewed and assessed. In addition, complementary information on the electronic and molecular structure of the molecule and on electron detachment and ion transport in parent gas is provided that allows a better understanding of the nature of the cross sections and swarm parameters. The assessed data are used to deduce cross sections and coefficients for which there exist no direct measurements at the present time. The present work on electron interactions with the molecule reveals a rather simple picture which can be summarized as follows: (1) Elastic electron scattering is the most significant electron scattering process over the electron energy range from to (2) Below 15 eV the most distinct inelastic energy-loss process is vibrational excitation—direct dipole excitation involving the mode and indirect vibrational excitation via negative ion states involving the mode. (3) Below electron attachment forming is the most dominant interaction (along with elastic scattering). Above this energy, the cross sections for dissociative electron attachment forming fragment anions [principally ( 4, and 5) and ] are appreciable, with the room temperature total electron attachment cross section dominated by the formation of between and 1.5 eV and by the formation of beyond (4) Above dissociativeionization becomes significant, generating principally ( 3, 4, and 5) and positive-ion fragments which, together with elastic electron scattering, makes up most of the total electron scattering cross section. (5) Electron-impact dissociation into neutral fragments ( 2, and 3) and F occurs above with cross section values potentially exceeding those for ionization for electron energies near 20 eV. (6) The total electron scattering cross section exhibits distinct structure due to negative-ion resonances near 0.0, 2.5, 7.0, and 11.9 eV. The most significant data needs are for direct measurements of vibrational excitation cross sections, for cross sections for electron-impact dissociation into neutral fragments, and for the momentum transfer cross section at low energies.
Thermodynamic Properties of Air and Mixtures of Nitrogen, Argon, and Oxygen From 60 to 2000 K at Pressures to 2000 MPa29(2000); http://dx.doi.org/10.1063/1.1285884View Description Hide Description
A thermodynamic property formulation for standard dry air based upon available experimental 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%.
Temperature Dependence of Physical–Chemical Properties of Selected Chemicals of Environmental Interest. II. Chlorobenzenes, Polychlorinated Biphenyls, Polychlorinated Dibenzo-p-dioxins, and Dibenzofurans29(2000); http://dx.doi.org/10.1063/1.1286267View Description Hide Description
Data are compiled and reviewed of the physical–chemical properties of chlorinated benzenes, biphenyls, and dibenzo--dioxins and dibenzofurans, which control air–water partitioning, namely vapor pressure, aqueous solubility, and Henry’s law constant over the environmentally relevant temperature range of Recommended values at and equations for estimating these properties over the temperature range of are provided. Corresponding enthalpies of phase transition are also reported.
The Ideal Gas Thermodynamics of Diesel Fuel Ingredients. I. Naphthalene Derivatives and Their Radicals29(2000); http://dx.doi.org/10.1063/1.1288947View Description Hide Description
The molecular fundamentals of 21 naphthalene derivatives were investigated, calculated and evaluated, and their ideal gas thermodynamicproperties were calculated, for the sake of simulating the combustionproperties of diesel fuel. Ten of these species are stable molecules and 11 are radicals. The molecular fundamentals are calculated using Gaussian 94 ab initio and MOPAC 6semiempirical programs. The results can be used to estimate the MOPAC performance with polyaromatic species.