Takako Shinoda

Heat Capacity of CoCl2·2H2O between 7 and 120°K and its Anomaly Associated with Magnetic Transition

A small adiabatic calorimeter is described, which is capable of measuring the solid heat capacities between 5° and 300°K continuously. The heat capacities of CoCl 2 ·2H 2 O were measured between 7° and 120°K. A lambda-shaped anomaly in the heat capacity, due apparently to a transition between antiferromagnetic and paramagnetic states, occurs below 20°K with the peak at 17.20°K. An analysis of the experimental heat capacity curve was made in the light of the series expansion method through help of the experimental heat capacities of CoCl 2 ·6H 2 O at the low temperatures in a semi-empirical way. This result gives the exchange interactions | J |/ k =10.8°K in the direction of the chain of the coordinated Co 2+ ions and | J |/ k =2.03°K between Co 2+ ions in the neighboring chains. The total entropy of the transition is 1.39 cal/deg mole and about 37% of this is acquired in the temperature region above 17.20°K.

Thermodynamic properties of N-(p-methoxybenzylidene)-p-n-butylaniline (mbba) from 2 K to its isotropic-liquid phase

The heat capacity of N-(p-methoxybenzylidene)-p-n-butylaniline (mbba) was measured between 2 and 330 K with an adiabatic calorimeter. The crystal-to-nematic phase transition temperature is 295.654 K with an enthalpy of transition (3089.2±5.1) calth mol−1 and the nematic-to-isotropic phase transition temperature is 320.137 K with an enthalpy of transition (67.9±0.9) calth mol−1. A metastable solid state (intermediate state) is established below the freezing temperature by cooling from the nematic phase and then it is transformed into the stable crystalline state irreversibly with gradual heat evolution. The orientational and positional potential energies are estimated to be 3.5 to 3.6 kcalth mol−1 and 8.9 kcalth mol−1, respectively, from the experimental results on the basis of a theory of translational and orientational melting to liquid crystals. The purity of the sample is calculated from melting-temperature depressions and from premelting heat capacities.

Molecular Vibrations of Low Temperature Crystal of CO

A method is presented for finding the frequency distributions of lattice vibrations of the molecular crystals. The method is applied to solid carbon monoxide at low temperatures, making use of the observed far-infrared frequencies to check some of the molecular interaction constants, and frequency distributions are calculated. The values of heat capacity at low temperatures are evaluated using the calculated frequency distributions, and are compared with experimental data. The result shows that the treatment may be useful in discussing molecular vibrations in the lattice at low temperatures.

Intermolecular Potential for Silicon Tetrafluoride

We have examined to give a molecular potential for silicon tetrafluoride which describes accurately the interactions between molecules. It was found that the spherical interaction of the Lennard-Jones form and the electrostatic octopole-octopole interaction between neighboring molecules fails to explain the various physical properties of SiF 4 , whereas an addition of anisotropic Lennard-Jones potentials between nonbonded atoms gives a satisfactory account of these properties. The value of the potential parameters is evaluated and discussed by comparing with experimental data.