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A single crystal of 'orange' 1802 at 9.6 (3) GPa and 297 (1) K was produced in a Merrill-Bassett diamondanvil high-pressure cell and examined by X-ray diffraction. Pressure was determined with the rubyfluorescence method. The unit cell is orthorhombic, space group Fmmm, lattice constants a = 4.2151 (6), b = 2.9567 (4), c = 6.6897 (17)A, molar volume = 12.56 x 10 -6 m 3 mol -~ with four molecules per unit cell. The charge densities of the molecules overlap or distort to a considerable degree. Generalized scattering factors were used in an aspherical-atom least-squares * Work performed under the auspices of the US Department of Energy.0567-7408/83/020153-05501.50 refinement. For five refined parameters and 24 observations the final R w is 0.056. A correction is made to our previous work on fl-O2 at 5.5 GPa and 299 K.

A single crystal of N 2 at 49 kbar (4.9 GPa) and 299 K was produced in a Merrill-Bassett diamond-anvil high-pressure cell and examined by X-rays. Pressure was determined by the ruby-fluorescence method. The unit cell is cubic, a 0 -6. 164 (1) A, space group Pm3n, with eight molecules per unit cell. The structure is the same as that offl-F 2 and )-0 2 at 50 K and atmospheric pressure. For seven refined parameters and 19 observations the final R,,. is 0.0488.

Compressibility and specific heats of heavier condensed rare gases near the liquid-vapor critical point Influence of vibrational anharmonicity and vacancies on the thermodynamic properties of rare gas crystals Low Temp.A new two-parameter vapor pressure equation has been derived which, unlike the Salter equation, is shown to be equally applicable to quantum or classical solids and even liquids. The condensed phase enthalpies and entropies are given directly by the fitted parameters with accuracies comparable to those which have been claimed for existing independent calorimetric measurements. Recent vapor pressure data for the solid and liquid phases of argon, krypton, and xenon are analyzed in this manner, and the results are compared with the available calorimetric data. New values for the cohesive energy at T = 0 are also derived for these substances.