**6. Acknowledgment**

632 Thermodynamics – Interaction Studies – Solids, Liquids and Gases

comparative ebulliometry, the enthalpies of vaporization by evaporation calorimetry, and the low temperature heat capacity and phase transitions by vacuum adiabatic calorimetry. The saturation vapor pressures were determined in moderate range of pressure 2 (*p*/kPa) 101.6 with accuracy of the temperature 0.01 K, and pressure, 26 Pa, which correspond to the modern precision levels. The temperature dependences of the saturation vapor pressure, ln( ) ( ) *p F T* , and the enthalpies of vaporization *Hvap f* ( ) *T* were obtained by mathematical processing of the *pT* parameters by equation (1), derived on the basis of Clapeyron equation using LSM with orthogonal functions. The latter allow one to calculate the errors of *Hvap* values, which are urgent problem because the indirect method is the main source for determination of the enthalpies of vaporization. An agreement of the *Hvap* values obtained by direct (calorimetric) and indirect (calculation) methods proves

The precise saturated vapor pressure data are extended to entire region of the liquids under study. Extrapolation of the *pT* parameters down to the triple point temperature are carried out by simultaneous processing the vapor pressures and low-temperature differences 0 0 () ( ) *C C g C liq pm pm pm* ,, , , which are the second derivatives of the vapor pressure upon the temperature. Extending the *pT* parameters to the critical region and calculation of the critical quantities are performed by Filippov's one-parameter law of the corresponding states. The latter enables us both to calculate the critical parameters on the basis of more readily available *pT* -data and density of liquids and to predict numerous thermo-physical properties of the equilibrium liquid – vapor by means of the known critical quantities*T* , *c V* , *c* and

The low temperature heat capacity in the temperature region (5 to 373) K, molecular motion in crystal and metastable phases, and solid state transitions and fusion were investigated by the adiabatic calorimetry. Uncertainties of the*Cp*,*m* measurements are on the average ~0.2 %

An accurate calorimetric study of the solid states of the functional organic compounds revealed different polymorphic modifications of the molecules, order – disorder transitions involving orientational and conformational disorder, glass-like transitions, and plastic crystalline phases with anisotropic and isotropic reorientations of the molecules. For interpretation of these transformations, the X-ray crystallography, infrared and Raman

The main thermodynamic functions in three aggregate states: the absolute entropy by the 3d law of thermodynamics, the changes of the enthalpy and free Gibbs energy are derived on the basis of the heat capacity and vapor pressure measurements. A critical analysis and verification of the reliability of obtained data are very significant parts of the thermodynamic investigation. With this in mind, the experimental thermodynamic functions are compared with calculated ones by additive principles and by statistical thermodynamics coupled with quantum mechanical (QM) calculation on the basis of DFT method. The QM calculation are performed on the level B3LYP/6-31G(d,p) by Gaussian 98

A qualitative analysis of thermodynamic properties in dependence on some parameters responsible for intermolecular interactions and short range order of the liquid phase has been carried out for verification of the mutual consistency of the properties in homologous series and the series of the same type of compounds. A quantitative verification of the

their reliability.

criterion of similarity *A*

and 03 software packages.

*F* .

which correspond up-to-date precision level.

molecular spectroscopy were got involved in investigation.

We are grateful to Professor O. Dorofeeva for providing Gaussian programs and assistance in quantum-chemical calculations of the ideal gas thermodynamic functions. Many thanks to Professor S. Verevkin for helping in determination of the vapor pressures of some derivatives of ferrocene and Dr. L. Pashchenko for taking part in determination of the vapor pressures of some freons. Special thanks are to Post-graduate student E. Tkachenko for providing illustrative materials of the chapter.

This work was financially supported by Russian Foundation for Basic Research under Grants No. 96-02-05445 and No. 05-02-17435.
