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Notes: Ab initio potentials for the X 2Σ+1/2, A1 2Π3/2, and A2 2Π1/2 states of ArHe+ are tested as to their ability to describe swarm measurements of gaseous ion transport coefficients. Also tested are potentials based on spectroscopic measurements and model potentials chosen specifically so as to match the transport data. Ar+-ion velocity distributions in a drift tube containing a helium buffer are calculated from the potentials that best match the mobility data, by solution of the Boltzmann kinetic equation. The velocity distributions are used with estimated cross sections for the charge-transfer reaction Ar++N2 to calculate the effects upon the rate coefficients when the distribution differs from a Maxwell–Boltzmann form. The results indicate that the corrections are small at high buffer gas temperatures (293 K and above) and low to moderate electric-field strengths, but become larger at low temperature (82 K) and high fields. The smallness of the corrections confirms that previous rate coefficient measurements in a drift tube show a dependence of the Ar++N2 reaction upon the rotational temperature of N2.

Notes: An analytical equation of state for a d-dimensional fluid is presented, obtained as a generalization of a successful result for d=3. Agreement with available computer simulations and virial coefficients for d=1,2,4, and 5 indicates that the generalization is accurate.

Notes: We present a new strong principle of corresponding states that reduces the entire pressure–volume–temperature (p–v–T) surface of a nonpolar fluid to a single curve; this curve corresponds to an effective pair distribution function at contact as a function of reduced density. This reduction of a surface to a curve is based on statistical-mechanical theory, which also furnishes the algorithms for calculating, from the intermolecular pair potential, the three temperature-dependent parameters needed for the reduction. If the pair potential is not known, data on the second virial coefficient as a function of temperature can be used instead. The principle is tested on a computer-simulated Lennard-Jones (12,6) fluid, on the noble-gas fluids (except He), on N2, CO2, CF4, SF6, and on the first four alkanes. A suitable reciprocal plot yields virtual straight lines for all the real fluids, which differ in shape from the expected Carnahan–Starling curve that describes the (12,6) fluid; we suggest that these shape differences are caused by many-body forces in the real fluids. By curve fitting straight lines to the empirical data for the real fluids, we obtain a simple analytic equation of state, cubic in the density, that can be characterized by three constants: the Boyle temperature, the Boyle volume, and a slope constant. This equation is not accurate in the nonanalytic critical and two-phase regions, but otherwise describes the volumetric behavior of nonpolar fluids very accurately over the entire range from the dilute gas to the dense liquid. It has considerable predictive power, since it permits the construction of the entire p–v–T surface from just the second virial coefficient plus a few liquid densities.

Notes: A universal scaling scheme is developed for closed-shell interactions. The exchange energies (total energies minus the Coulombic energies) are found to scale with two parameters to universal interaction curves for noble gas–noble gas, alkali ion–noble gas, and halogen ion–noble gas interactions. The interaction potentials constructed from the universal interaction curves agree well with experimentally determined potentials, and also successfully reproduce measured ion mobilities and diffusion coefficients. The universal interactions can be viewed not just as a correlation scheme, but also as operating to extend the range of the potentials for a number of ion–atom systems to both larger and smaller distances than are presently probed by direct measurements. They also provide the basis for predictions of potentials for systems lacking experimental measurements. In the case of the noble gases, they reduce by two the number of parameters required for the formulation of an accurate extended principle of corresponding states.

Notes: We present an analytical equation of state based on statistical-mechanical perturbation theory for hard spheres, using the Weeks–Chandler–Andersen decomposition of the potential and the Carnahan–Starling formula for the pair distribution function at contact, g(d+), but with a different algorithm for calculating the effective hard-sphere diameter. The second virial coefficient is calculated exactly. Two temperature-dependent quantities in addition to the second virial coefficient arise, an effective hard-sphere diameter or van der Waals covolume, and a scaling factor for g(d+). Both can be calculated by simple quadrature from the intermolecular potential. If the potential is not known, they can be determined from the experimental second virial coefficient because they are insensitive to the shape of the potential. Two scaling constants suffice for this purpose, the Boyle temperature and the Boyle volume. These could also be determined from analysis of a number of properties other than the second virial coefficient. Thus the second virial coefficient serves to predict the entire equation of state in terms of two scaling parameters, and hence a number of other thermodynamic properties including the Helmholtz free energy, the internal energy, the vapor pressure curve and the orthobaric liquid and vapor densities, and the Joule–Thomson inversion curve, among others. Since it is effectively a two-parameter equation, the equation of state implies a principle of corresponding states. Agreement with computer-simulated results for a Lennard-Jones (12,6) fluid, and with experimental p–v–T data on the noble gases (except He) is quite good, extending up to the limit of available data, which is ten times the critical density for the (12,6) fluid and about three times the critical density for the noble gases.As expected for a mean-field theory, the prediction of the critical constants is only fair, and of the critical exponents is incorrect. Limited testing on the polyatomic gases CH4, N2, and CO2 suggests that the results for spherical molecules (CH4) may be as good as for the noble gases, nearly as good for slightly nonspherical molecules (N2), but poor at high densities for nonspherical molecules (CO2). In all cases, however, the results are accurate up to the critical density. Except for the eight-parameter empirical Benedict–Webb–Rubin equation, this appears to be the most accurate analytical equation of state proposed to date.

Notes: Mobilities of O+ and O− ions in He gas have been measured as a function of electric field strength at temperatures from 93 to 568 K. The results are compared with previous work, and analyzed in terms of a temperature-field strength scaling rule and the O+–He and O−–He potentials. Emphasis is placed on how much information on the potentials can be obtained from simple features of the mobility curve without extensive numerical computation.

Notes: Potential energy curves for the three lowest states of HeNe+(X 2Σ1/2+,A1 2Π3/2,A2 2Π1/2) are determined from a combination of mobility and spectroscopic measurements, in conjunction with a theoretical expression giving the A1 curve in terms of the X and A2 curves plus the energy splitting between the 2P3/2 and 2P1/2 states of Ne+. The results are also consistent with measurements of the scattering of beams of fast Ne+ ions by He gas. The best available ab initio potentials give mobilities in poor agreement with experiment, largely because of poor predictions of the positions of the potential minima. It is also shown that, contrary to initial expectations, mixture formulas for mobility based on simple momentum-transfer theory are valid for open-shell systems with multiple interaction potentials. Illustrative calculations are given for the mobility of Ne+ in a He+Ne mixture; both HeNe+ and Ne2+ have multiple potentials.

Notes: The theory of thermal diffusion in ionized gases is reconsidered taking into account quantal effects and effects caused by dynamic shielding. Quantal effects arise because it is only in a small range of intermediate energies that the de Broglie wavelength is negligible relative to the effective collision diameter. Dynamic shielding effects are caused by the lack of instant response to particle motion by the charged particle sea surrounding them and are important at low temperatures and high electron densities. The errors incurred by the omission of these effects can usually be ignored in planetary ionospheres or in the solar corona, but are by no means negligible under conditions characteristic of the solar interior. Similar, but not identical, results were found for calculations of the binary diffusion coefficient.