A theory of the reaction rate of simple exchange reactions in the gas phase is developed on the basis of the quantum-statistical mechanical theory of linear irreversible processes due to Kubo et al. A formal expression for the rate coefficient is found near the equilibrium point. A number of relations are derived concerning the scattering amplitudes for the collisions involved in the above reactions. By making use of these relations, the rate constant is expressed in terms of the reaction cross sections in a way which coincides with that known from a more intuitive collisional approach. Since no ad hoc assumptions are made, the present theory can be said to provide a statistical mechanical foundation for the collision theory in the particular case discussed.

Empirical evidence suggests that three-dimensional (3D) images of nature promote physiological relaxation in humans by providing more realistic effects compared with two-dimensional (2D) images. However, no studies have evaluated the physiological relaxation effects of nature-derived 3D images on prefrontal cortex and autonomic nerve activity. The present study aimed to clarify the physiological relaxation effects of visual stimulation by 3D flower images on prefrontal cortex and autonomic nerve activity. Nineteen male university students (22.2 ± 0.6 years) were presented with 3D and 2D images of the water lily for 90 s. Prefrontal cortex activity was measured using near-infrared spectroscopy, while autonomic nerve activity was measured using heart rate variability (HRV). Psychological effects were determined using a modified semantic differential method (SD). Compared with visual stimulation by 2D images, that by 3D images resulted in a significant decrease in oxyhemoglobin concentration in the right prefrontal cortex, lower sympathetic activity as calculated by the ratio of the low-frequency to high-frequency HRV component, and a significantly greater realistic feeling as evidenced by higher SD ratings. In conclusion, visual stimulation by realistic 3D floral images promotes physiological relaxation more effectively than the corresponding 2D image.

Thermal, spectroscopic, and other properties of methane solids, especially those concerning Phase II of solid CH4 in nuclear spin species equilibration, are theoretically studied from a unified point of view, i.e., the extended James–Keenan model. It assumes a rigid lattice and treats the molecular motions with respect to the rotational degress of freedom in the crystal potential given by Yasuda [Prog. Theor. Phys. 45, 1361 (1971)]. Two adjustable parameters are introduced in order to adapt the assumed crystal potential to the actual situation in the solid state of CH4. Most of the calculations are carried out in the framework of the molecular field method in quantum statistical mechanics. The eight-sublattice antiferrorotational structure is assigned to Phase II. Thus we have two kinds of site Hamiltonians in this phase, the symmetry groups of which are the direct product groups ?hOh and ?dD2d. Basis functions are doubly symmetry adapted under each of these symmetry groups. Rotational functions are included up to J=8 (sometimes up to J=10). The accuracy of the calculations is tested and the errors in level spacings are estimated at a few percent. The level scheme obtained for Oh-site features hindered rotations, is independent of temperature, and applies also to all molecules in Phase I. The level scheme of D2d site bears the librational character in its lower energy part and has the lowest levels split through quantum tunneling (the tunneling levels). These level schemes are compared with the results of neutron inelastic scattering experiments and satisfactory agreements are obtained. The two-term crystalline field employed is justified through comparison with the result of the neutron diffraction experiment on Phase I of CD4. The transition between Phases I and II turns out to be of first order, and the reason for this is given. The nature of the transition is new, being neither the rotational melting proposed by Pauling nor the orientational order–disorder transition by Frenkel. Thermodynamic quantities are worked out, including the free energy, entropy, internal energy, specific heat, and the mean square of the proton spin angular momentum. Anomalous behaviors of the specific heat at low temperatures are studied in detail and compared with observation. The predicted structure of the tunneling levels is again and conclusively confirmed by experiment. The negative thermal expansion observed below about 10 K is nicely reproduced with an additional assumption on the response of the crystal potential upon varying the lattice spacing. The transition between Phases II and III observed at elevated pressure is qualitatively discussed with special reference to the role played by Oh molecules in Phase II, and a quantum nature of the transition below about 10 K is pointed out. The main predictions made in this report are as follows: (1) The tunneling levels have such temperature dependences below about 4 K that their level spacings at 0 K are about 10% larger than those at 4 K. Their effects on the Schottky anomaly in the specific heat and on the nuclear susceptibility at around 1 K are described in detail. (2) Apparently unusual quantum effects are predicted on the transition temperatures between Phases I and II. That of CD4 is the highest and those of CH4 and CT4 appear at about the same temperature. (3) Solid solutions of CH4 and Kr or Xe have double phase transitions in a certain CH4-rich region, the lowest temperature phase having no orientational order. If the conversion is not allowed, the lower transition does not occur. (4) Solid solutions of CH4 and CD4 have triple transitions in a certain CH4-rich region, the lowest temperature phase having the same structure as Phase II. (5) The tunneling levels of T species split into two levels, the upper one has the degeneracy six and the lower one the degeneracy three, and the separation is 0.01 K.

A recent high pressure experiment on LaAlO3 has revealed that the compound is an exception for the "general rule" of displacive phase transition associated with zone-boundary phonons. In the present study, the experimental result is successfully confirmed by first principles calculations. The pressure dependence of phonon frequencies as well as the phase transition pressure is quantitatively well reproduced. We found that the behavior is not peculiar to LaAlO3 but rather ubiquitous. RAlO3 (R = La, Nd, Sm, and Gd) and LaGaO3 can be classified in the same group.