Evan H. Abramson

The elastic constants of San Carlos olivine to 17 GPa

All elastic constants, the average bulk and shear moduli, and the lattice parameters of San Carlos olivine (Fo90) (initial density 3.355 gm/cm3) have been determined to a pressure of 12 GPa at room temperature. Measurements of c11, c33, c13, and c55 have been extended to 17 GPa. The pressure dependence of the adiabatic, isotropic (Hashin-Shtrikman bounds) bulk modulus, and shear modulus may be expressed as KHS = 129.4 + 4.29 P and by GHS = 78 + 1.71P - 0.027 P2, where both the pressure and the moduli are in gigapascals. The isothermal compression of olivine is described by a bulk modulus given as KT = 126.3 + 4.28 P. Elastic constants other than c55 can be adequately represented by a linear relationship in pressure. In the order (c11, c12, c13, c22, c23, c33, c44, c55, c66) the 1 bar intercepts (gigapascal units) are (320.5, 68.1, 71.6, 196.5, 76.8, 233.5, 64.0, 77.0, 78.7). The first derivatives are (6.54, 3.86, 3.57, 5.38, 3.37, 5.51, 1.67, 1.81, 1.93). The second derivative for c55 is −0.070 GPa−1. Incompressibilities for the three axes may also be expressed as linear relationships with pressure. In the order of a, b, and c axes the intercepts in gigapascals are (547.8, 285.8, 381.8) and the first derivatives are (20.1, 12.3, 14.0).

Sound Velocities in Olivine at Earth Mantle Pressures

The independent elastic constants of an upper mantle mineral, San Carlos olivine [(Mg1.8Fe0.2)SiO4], were measured from 0 to 12.5 gigapascals. Evidence is offered in support of the proposition that the explicit temperature dependence of the bulk modulus is small over the range of temperatures and pressures thought to prevail above the 400-kilometer discontinuity, and thus the data can be extrapolated to estimate the properties of olivine under mantle conditions at a depth of 400 kilometers. In the absence of high-temperature data at high pressures, estimates are made of the properties of olivine under mantle conditions to a depth of 400 kilometers. In contrast with low-pressure laboratory data, the predicted covariance of shear and compressional velocities as a function of temperature nearly matches the seismically estimated value for the lower mantle.

Synergy between Secondary Organic Aerosols and Long Range Transport of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs), known for their harmful health effects, undergo long-range transport (LRT) when adsorbed on and/or absorbed in atmospheric particles. The association between atmospheric particles, PAHs, and their LRT has been the subject of many studies yet remains poorly understood. Current models assume PAHs instantaneously attain reversible gas-particle equilibrium. In this paradigm, as gas-phase PAH concentrations are depleted due to oxidation and dilution during LRT, particle-bound PAHs rapidly evaporate to re-establish equilibrium leading to severe underpredictions of LRT potential of particle-bound PAHs. Here we present a new, experimentally based picture in which PAHs trapped inside highly viscous semisolid secondary organic aerosol (SOA) particles, during particle formation, are prevented from evaporation and shielded from oxidation. In contrast, surface-adsorbed PAHs rapidly evaporate leaving no trace. We find synergetic effects between hydrophobic organics and SOA - the presence of hydrophobic organics inside SOA particles drastically slows SOA evaporation to the point that it can almost be ignored, and the highly viscous SOA prevents PAH evaporation ensuring efficient LRT. The data show the assumptions of instantaneous reversible gas-particle equilibrium for PAHs and SOA are fundamentally flawed, providing an explanation for the persistent discrepancy between observed and predicted particle-bound PAHs.

The thermal diffusivity of water at high pressures and temperatures

Thermal diffusivities of fluid water have been measured to a pressure of 3.5 GPa, a density of 1.4 g cm−3 and a temperature of 400 °C. Above 100 °C, both the diffusivities and the related conductivities are found, unexpectedly, to scale as the square-root of absolute temperature; in contrast, the excess conductivities are highly dependent on temperature. Measurements at 25 °C, extending into a metastable regime with respect to ice VI, do not scale in this manner and this anomalous behavior is not suppressed by pressures up to 1.3 GPa.

SPEED OF SOUND AND EQUATION OF STATE FOR FLUID OXYGEN TO 10 GPA

The speed of sound in supercritical, fluid oxygen has been measured up to the freezing points of 6.0 GPa at 30 °C and 10.5 GPa at 200 °C. The oxygen was contained in a diamond–anvil cell and pressure was measured on the ruby scale. The measurements were used to establish an equation of state. Additionally, the fluid-β phase boundary was determined between 15 and 180 °C to a precision of 0.02 GPa.

A linear 1B2 state of the water molecule

Spectra of the lowest 1B2 state of H2O and D2O have been recorded. The state is linear in its equilibrium geometry and has a bond length of 1.02 A. The spectra exhibit vibrational bending progressions and are rotationally resolved. They were recorded from energies of 80 000 to 90 000 cm−1 via two‐photon, laser‐induced flourescence (LIF) and 2+1 multiphoton ionization (MPI).

Elastic constants, interatomic forces, and equation of state of β‐oxygen at high pressure

The six independent elastic constants of β‐oxygen have been measured over a pressure range extending from 6.0 to 9.5 GPa. Neither central forces between individual atoms, nor central forces augmented by the interactions between axial distributions of charge can give a reasonable account of the data. Force constant matrices were found which can account for the elastic data and the previously observed librational frequency. These matrices are based on general, short range forces with many‐body interactions only among atoms contained in the same pair of molecules. Vibrational densities of states, distributions of individual‐mode Gruneisen parameters, heat capacities, and the equation of state derived from the pressure dependence of the elastic moduli are presented.

Melting curves of argon and methane

The melting curves of argon and of methane have been measured in a diamond-anvil cell from 290 to>700 K. Measurements of argon, fit to the equation P−6.9×10−5=0.244[(T/83.805)1.476−1], are in excellent agreement with previously published values up to a temperature of ∼ 500 K and thereafter diverge slowly. Measurements of methane, fit to P−1.17×10−5=0.208[(T/90.6941)1.698−1], are in serious disagreement with the only previous studies to extend past 400 K.

Thermal diffusivity of fluid oxygen to 12 GPa and 300 °C

The thermal diffusivity of fluid oxygen in the diamond-anvil cell has been measured from 1 to 12.6 GPa and 25 to 300 °C. These constitute the first experimental measurements of thermal transport properties of simple fluids above 1 GPa. Diffusivities are found to rise sharply from a minimum at intermediate pressures and then to level off at ∼6 GPa. Thermal conductivities derived from these measurements do not vary as √T, rather the excess conductivities are approximately independent of temperature. The diffusivities of nitrogen, previously measured to 1 GPa, closely match those of oxygen when scaled as suggested by a simple, corresponding states theory.

The shear viscosity of supercritical oxygen at high pressure

Shear viscosities of supercritical oxygen have been measured up to a pressure of 5.7 GPa at 294 K. A modified free-volume expression fits the data within 6% between the limits of the tenuous gas and 4.8 times the critical density. Nitrogen viscosities were found to correspond to those of oxygen through a simple scaling by critical constants. Viscosities were measured in the high-pressure diamond-anvil cell with a rolling-ball technique. The dynamics of a sphere rolling on an inclined plane were investigated in the context of these experiments. The effect of a second surface, situated above the sphere, was experimentally determined.