ИСТИНА

During the hypersonic spacecraft reentrance into the upper atmosphere of solar system planets high-speed gas-plasma medium is formed. To probe the fundamental energy exchange processes between the internal degrees of freedom of atoms and molecules in such highly heated medium thermodynamic, transport and radiative properties of real gases at the tempera-ture T up to 50 000K are necessary. To this end, the statistical calculations should apparently account for both interatomic and intramolecular (non-adiabatic) interactions taking place between the constituent particles. Furthermore, under this non-equilibrium condition calculating the molecular radiation transfer is severely complicated due to the fact that the description of radiation process involves complex chemistry and requires detailed information about the available molecular states. We examine the feasibility of applying the classical and semi-classical theories for the description of high-temperature molecular spectra by comparing approximate calculations of emission and absorption coefficients with the result of tedious quantum-mechanical calculations. Compared with a quantum-mechanical rovibrational description, it requires far less computation time. Our eventual aim is to determine whether the semi-classical theory allows us to quickly calculate molecular thermodynamic and radiation characteristics without compromising significant accuracy. As examples, (1) the internal partition function and specific heat of nitro-gen dimer have been evaluated in a wide range of the temperature using clas-sical statistical mechanics; (2) the photodissociation cross-section of the Schu-mann-Runge bound-continuum transitions of oxygen dimer have been calcu-lated in the framework semi-classical approximation as a function of vibrational temperature. In general, at high temperature, a good agreement is observed. In the case of low temperatures (ωe>>kT) the calculation should be carried out by the quantum method and non-adiabatic interaction should be often taken into account. At high temperatures (ωe<<kT) the calculation could be carried out with appropriate accuracy in the framework of classical mechanics while at in-termediate temperatures (ωe~kT) a semi-classical correction is necessary to imply. The full form of the interacting-particle partition function is found to be essential to complete and correct calculation of the thermodynamic functions of the systems. Obviously, conventional methods which include only the bound-state sum in partition function become in error since it introduces discontinuities into the thermodynamic-state function at those points where the bound-state levels pass into the continuum. The work has been partially supported by the RFBR grant 11-03-00307а and 7th European framework program grant 242311.