CHD2 + D2 -CHD3 + D (17)These consecutive reactions take place in the same cavitation event.Among the higher hydrocarbons, acetylene is the major product at medium concentrations of CH4 + H2 (Figure 5). However, at higher concentrations the yields of ethane and ethylene are greater. This effect indicates lower temperatures in the cavitation bubbles when much CH4 + H2 is present.At the present time it is difficult to give a more detailed mechanism for the reactions observed. With respect to the deuterium exchange it would be interesting to study the pyrolysis of mixtures of CH4 and D2 and to make a comparison with the data obtained in sonolysis. Our present findings again show that very drastic temperature conditions exist in the cavitation bubbles which act as microsystems for the pyrolysis of gases surrounded by a cold water bath in which many products of pyrolysis are rapidly cooled and stabilized.

Pressure-volume-temperature relations of the liquid, the supercooled liquid, the crystal, and the glass are reported. From isochoric comparisons of the entropy of the amorphous states with the entropy of the crystal, the excess amorphous entropies are discussed with the help of the calorimetric data by Chang and Bestul. The ex-entropy of the glass is almost independent of volume and temperature, amounts to 1.4R, which consists of the intra-and intermolecular contributions, and is smaller than the residual entropy of the glass at 0 K. The excess entropy of the liquid considerably depends on volume and seems to be asymptotic to 4.6-5.OR at the zero density extreme near the room temperature. In a series of systematic tests on the factors determining the glass transition temperature and the dielectric relaxation time in the supercooled liquid state, various configurational quantities are examined. The most suitable factor is the configurational internal energy or entropy defined as the excess quantity over the crystal at constant temperature and pressure. These factors are expected to apply generally to the nonassociated liquids including polymer liquids.

monomer-aggregate equilibrium. However, it should be noted that the range of porphyrin concentrations utilized in this study for both the NMR and ESR experiments was small (lO'MO""1 23 M) and the data therefore do not provide definitive evidence which would rule out the possibility that a stable aggregate of the tetra cationic porphyrin (such as a true dimer) might be formed under the above solution conditions. Nevertheless, the results in this work clearly demonstrate the presence of only monomers in SDS solutions.Acknowledgment. The support of the National Science Foundation (Grant CHE-8822981) is gratefully acknowledged.

The equilibrium αβ transition temperature, T αβ, between the α crystalline phase and the β crystalline phase of resorcinol has been determined when both supercooling and superheating effects vanished. The latent volume and dT αβ/dP have been determined by use of a precision pycnometer, and the thermodynamic characteristics of the αβ transition are presented. The P − V − T relations of each phase have also been obtained. All of the thermal expansion coefficient, the isothermal compressibility, and the internal pressure for the higher-temperature, higher-density polymorph, the β crystal, are much larger than those for the lower-temperature, lower-density polymorph, the α crystal. Contributions of the hydrogen bonds and the van der Waals energy to the internal energy have semiquantitatively been analyzed by use of a simple potential model. When the α crystal transforms to the β crystal, the energy of hydrogen bonds decreases due to the breakdown of the hydrogen bonds, whereas the van der Waals energy increases with the contraction in volume. Since the latter cancels the most of the former, we observe the small latent heat. The breakdown of the hydrogen bonds induces a significant change in the potential depths of the covalent structure O−H···O and ionic, proton-transferred structure O-···H−O+ in each hydrogen bond. In consequence, the distribution of the protons between the covalent structure and the ionic structure changes with the transition. The increase in the entropy produced from the redistribution of the protons is the same order of magnitude as the latent entropy.

Hydroquinone crystals have been found to undergo first-order phase transition to a denser polymorph with an enthalpy increment, as does resorcinol. The phase stable at room temperature (called R) transforms to the new phase (designated δ) only under elevated pressures. P-V-T relations of the new phase have been measured, and characteristics of the transitions and the triple point among the R phase, the δ phase, and the liquid have been estimated from the thermodynamic consistency. The thermal expansion coefficient, the internal pressure, and the heat capacities of the δ phase are significantly larger than those of the R phase. Rigid-body vibrations and/or librations may play an important role in the Rδ transition. Contributions of hydrogen bonds and the structure of the δ phase are discussed.