Effect Of Intermolecular Potential Research Articles

Effect of intermolecular potential on compressible Couette flow in slip and transitional regimes

The effect of intermolecular potentials on compressible, planar flow in slip and transitional regimes is investigated using the direct simulation Monte Carlo method. Two intermolecular interaction models, the variable hard sphere (VHS) and the Lennard-Jones (LJ) models, are first compared for subsonic and supersonic Couette flows of argon at temperatures of 40, 273, and 1,000 K, and then for Couette flows in the transitional regime ranging from Knudsen numbers (Kn) of 0.0051 to 1. The binary scattering model for elastic scattering using the Lennard-Jones (LJ) intermolecular potential proposed recently [A. Venkattraman and A. Alexeenko, “Binary scattering model for Lennard-Jones potential: Transport coefficients and collision integrals for non-equilibrium gas flow simulations,” Phys. Fluids 24, 027101 (2012)] is shown to accurately reproduce both the theoretical collision frequency in an equilibrium gas as well as the theoretical viscosity variation with temperature. The use of a repulsive-attractive instead of a purely repulsive potential is found to be most important in the continuum and slip regimes as well as in flows with large temperature variations. Differences in shear stress of up to 28% between the VHS and LJ models is observed at Kn=0.0051 and is attributed to differences in collision frequencies, ultimately affecting velocity gradients at the wall. For Kn=1 where the Knudsen layer expands the entire domain, the effect of the larger collision frequency in the LJ model relative to VHS diminishes, and a 7% difference in shear stress is observed.

Rovibrational matrix elements of the multipole moments and of the polarizability of the H2 molecule in the solid phase: Effect of intermolecular potential

Rovibrational matrix elements of the multiple moments Q l up to rank 10 and of the linear polarizability of the H2 molecule in the condensed phase have been computed taking into account the effect of the intermolecular potential. Comparison with gas phase matrix elements shows that the effect of solid state interactions is marginal.

Nonequilibrium Molecular Dynamics Simulations of 3-Methylhexane: The Effect of Inter- and Intramolecular Potential Models on Simulated Viscosity

Nonequilibrium molecular dynamics simulations of viscosity were performed using various molecular representations of 3-methylhexane in order to study the influence of potential models on simulated viscosity. The models investigated were united atom models with fixed bond lengths and bond angles. The effect of intermolecular potential was examined by comparing results from a homogeneous (in which all -CHx groups are equivalent) model and two heterogeneous models. The effect of intramolecular potential was investigated by comparing results from three different torsional potential models. The simulations were carried out at three different densities to investigate the sensitivity of the contributions from the various models to the viscosity at different conditions. Large changes in viscosity were produced by relatively small changes in the intermolecular potential parameters of the branched methyl group. The viscosity was found to be less sensitive to the intermolecular potential parameters of the chain methyl groups and the torsional potential. Our results suggest that an accurate representation of the molecular structure and size as governed by intermolecular interactions is more important in accurate viscosity predictions than careful modeling of the intramolecular potential.

Kinetic equations for Enskog gases with piecewise constant intermolecular potentials

The Boltzmann equation, which is central to the description of many linear and nonlinear transport processes, is the equation of an ideal gas of point molecules. The Enskog equation was proposed to model the finite diameter of molecules of real gases, but does not include the effects of intermolecular potentials. We describe some models which include a finite range approximation of such intermolecular potentials. In particular, we outline the existence of weak global-in-time solutions for a kinetic equation with piecewise constant intermolecular potential.

Inner-shell spectroscopies of solid and gaseous alkylidyne tricobalt nonacarbonyl complexes

Inner-shell excitation spectra of two alkylidyne tricobalt nonacarbonyl complexes, Co3(CO)9C—X (X = Cl, OCH3), have been recorded at the C 1s, O 1s, Co 2p and Co 3p edges using electron energy-loss (EELS) and photoionisation yield techniques for gas-phase studies and synchrotron radiation photo-ionisation with total electron yield detection for solid-state studies. This comparison was undertaken to provide cross-checks on the experimental techniques; to evaluate the dependence of spectral shape on the detection scheme employed; and to search for effects of intermolecular potentials on the core-excitation spectra of solids. A common set of (core → valence) spectral features are observed by all techniques although some additional minor features are found in specific spectral modes. There are systematic deviations between the oscillator strength for absorption (derived from the EELS data) and that for ionisation (derived from the total ion yield) because the ionisation yield is different from discrete excitation versus continuum ionisation. The ionic fragmentation of the C 1s excited and ionised Co3(CO)9CCl complex was investigated using a time-of-flight mass spectrometer for photoion and photoion–photoion coincidence yield studies. Extended Huckel molecular-orbital calculations were used to assist spectral interpretation. The merits of these experimental and computational techniques for systematic investigations of the electronic structure of large organometallic complexes are demonstrated.

Density and temperature dependence of the relaxation of the 1Δg state of highly compressed O2 fluid

Abstract The electronic relaxation of O 2 is investigated by an absorption excitation and fluorescence detection technique. The relaxation rate constant of O 2 ( 1 Δ g ) is measured in the density range from 10 21 to 3 × 10 22 cm −3 at temperatures between 90 and 295 K. The experimental results are compared with theoretical models based on the pair distribution functions of the fluid. The effects of intermolecular potentials with hard or soft cores are discussed.

The effects of intermolecular potentials on the vibrational spectra of condensed systems

AbstractThe effects of the Intermolecular interaction potential on the vibrational spectra of liquids or solutions are discussed for the cases where the molecular field can be treated as a time or space‐averaged quantity. It is shown that the introduction of an appropriate molecular field can yield information about molecular properties or about molecular arrangements of component molecules in the liquid and solution phases. Certain spectral characteristics, for instance absorption intensity in infra‐red spectra and scattering cross‐section and depolarization ratio in Raman spectra, are discussed.

Rarefied hypersonic flow about cones and flat plates by Monte Carlo simulation

Rarefied flow of a moiiatomic gas about slender cones and flat plates has been studied by a numerical experiment at Mach numbers of approximately 10 and 25 for both hot and cold wall conditions. Cone semiapex angle ranged from 3° to 15° while the ratio of ambient mean free path to body length was varied from 0.01 to 3.0. Leading edge flow on sharp slender cones is found to differ substantially from that on flat plates in that surface fluxes for the former do not show the large overshoots above free molecule values which exist for the latter geometry. Monte Carlo predictions of flowfield properties and surface fluxes are shown to be consistent, in the main, with experimental data. The effect of intermolecular potential in near-free-molecule flow about cones was investigated.