Using new high-temperature diamond-anvil-cell designs, together with a variety of optical techniques, we have measured the melting curves of N2 to 18.0 GPa, 02 to 16.3 GPa, and F2 to 2.5 GPa. One triple point is found on the N2 curve and two on the 02 curve. A simple "eff'ective rotation" model of librational motions in the solid is used to obtain good theoretical fits to the experimental curves.
components must refer to N2/Rh/Ti02.Although the integrated area for the N2 band in the 2250-cm-' region of Figure 9 was lower in each spectrum at a given pressure than was its analog in Figure 1, a Langmuir isotherm fit from the band area data in Figure 9 provided an adsorption equilibrium constant of 0.541 atm-i. This was significantly higher than the value (0.376 obtained from the data of ~i~~~~ 1. This indicata that the =avst r e d u d near SMSI -&tions J. Phys. Chem. 1992, 96, 7092-7096 the N2 infrared band were higher for the latter case. 4.High-pressure infrared studies are useful for obtaining equilibrium adsorption data at ambient and higher temperatures. Acknowledgment.We thank the Strategic Defense Initiative Organization's Office of Innovative Science and Technology through Contract N60921-91-C-0078 with the Naval Surface Warfare Center for support of this work. to a greater extent wGh N2 than did the one treated under mild reduction conditions. This is in agreement with the findings of Resasco and Haller for chemisorption measurements of N2 on Rh/Ti02 reduced at 473 and 773 K. 19 We must conclude that the integrated band areas of the 2250-cm-' band decreased in Figure 9 relative to Figure 1, not because of a decline in coverage but rather because of poor infrared transmission following hightemperature reduction. It should be noted that the integrated area for the N2 physisorption band at ca. 2330 cm-' increased slightly for the high-temperature reduced Rh/Ti02 and Ti02 films relative to those reduced at low temperature. This observation, although opposite to that for the N2 chemisorption band for Rh/Ti02, would seem to support the conclusions of Burch and Flambard that high-temperature reduced TiOz itself enhances N2 adsorption at 298 K.20 ConclusionsSeveral conclusions can be drawn from this work. 1. There is definitely a support effect on the chemisorption of N2 on supported Rh. For samples reduced at low temperature (473 K) and exposed to N2 at 298 K, the adsorption equilibrium constant was in the order Ti02 > AI2O3, SO2. Variable-temperature experiments forRh/Ti02 reduced under mild conditions provided a heat of adsorption for N2/ Rh/Ti02 extrapolated to zero coverage of -10.2 kcal/mol. 3. For a Rh/Ti02 film reduced under vigorous conditions (borderline SMSI), the N2 adsorption equilibrium constant at 298 K (0.541 atm-') was greater than for those reduced at lower temperature (0.376 atm-'), even though the integrated areas for References and Notes (1) Wey, J. P.; Burkett, H. D.; Neely, W. C.; Worley, S. D.Infrared and UV-visible absorption spectra have been obtained for samples of N2O4 contained in diamond-anvil cells at high pressures and high temperatures. Infrared spectra allow characterization of the phase and chemistry of N20, as a function of temperature and pressure, while UV-visible absorption spectra allow an independent measure of AH and correlation with previous measurements. Three new peaks appear in the IR spectra at low pressures and elevated temperatures in the liquid phase, one i...
The Raman spectra and phase diagram of fluorine were studied in a diamond-anvil cell up to 6 GPa over the temperature range 10–300 K. The sample slowly reacted with the diamond anvils to form CF4. The vibron frequencies in α-F2 and β-F2, as well as the lattice modes in α-F2, were determined as a function of pressure. No new phases were discovered. The α–β phase boundary can be fit with an equation of the Simon form: Pαβ (GPa)=−0.385(10) +4.80(9)×10−4 Tαβ1.75 (K). The melting curve was established to lie between limiting curves: Puppermelt (GPa)=−0.107+1.01×10−4T1.75melt (K) and Plowermelt (GPa)=−0.140+1.32×10−4 T1.75melt (K).
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