Molecular crystals are characterized by strong intramolecular forces and much weaker intermolecular forces. High-pressure spectroscopic studies provide useful data for refining the various model potentials which are used to predict of the physical properties of such systems as well as for the formation of various crystalline phases. | JOURNAL OF SCIENCE OF HNUE Mathematical and Physical Sci. 2014 Vol. 59 No. 7 pp. 119-125 This paper is available online at http MECHANICAL AND THERMODYNAMIC PROPERTIES OF CO2 AND N2 O MOLECULAR CRYOCRYSTALS UNDER PRESSURE Nguyen Quang Hoc1 Bui Duc Tinh1 and Nguyen Duc Hien2 1 Faculty of Physics Hanoi National University of Education 2 Mac Dinh Chi Secondary School Chu Pah District Gia Lai Province Abstract. The mechanical and thermodynamic properties such as the nearest neighbor distance the molar volume the adiabatic and isothermal compressibilities the thermal expansion coefficient and the heat capacities at constant volume and at constant pressure of molecular cryocrystals of many atoms with a face-centered cubic structure such as α-CO2 α-N2 O at various temperatures and at pressures up to 10 GPa are investigated using the statistical moment method SMM in statistical mechanics and compared with the experimental data. Keywords Molecular cryocrystal statistical moment method. 1. Introduction Molecular crystals are characterized by strong intramolecular forces and much weaker intermolecular forces. High-pressure spectroscopic studies provide useful data for refining the various model potentials which are used to predict of the physical properties of such systems as well as for the formation of various crystalline phases. CO2 is an important volatile component of the earth as well as other planets in the solar system. Its high-pressure behavior is therefore of fundamental importance in planetary science. CO2 is one of the model systems involving the π bonding and the hybridization properties of the carbon atom which are strongly affected by high pressure conditions. Pressure-induced transitions from molecular to nonmolecular CO2 crystals are systematically investigated using first-principle lattice dynamics calculation. Geometrically likely transition pathways are derived from the dynamical instability of the molecular crystals under high .
