Gas-phase Reaction Thermodynamics In Preparation Of Pyrolytic Carbon Via Propylene Pyrolysis And The Elastics Properties Of Ar@C₆₀

Density functional theory(DFT) and accurate model chemistry at G3(MP2) and G3//B3LYP levels of theory have been employed to explore the details of propylene pyrolysis gas-phase reaction thermodynamics. Geometries and vibrational frequencies for all of the possible species are calculated by B3PW91/6-31G(d). Standard thermodynamic data are derived by G3(MP2) and G3//B3LYP electronic energies combined with statistical thermodynamics. The data include heat capacities, entropies, enthalpies of formation and Gibbs free energies of formation at 298.15 K. Heat capacities and Gibbs free energies of formation at temperatures in 100-1500 K are calculated and fitted into analytical equations. The theoretical values are in excellent agreements with the available experimental values. Thus the theoretical predictions for all of the other species (stable intermediates in propylene pyrolysis) are believed reliable. Based on the thermo-chemical data, the equilibrium concentration distribution for all of the species in the temperature range of 100-1500 K (i.e. phase diagram) are calculated according to the chemical equilibrium principle. This work has supported the possibility of direct condensation of the high concentration carbon monomers and dimmers produced in the propylene pyrolysis dissociation reactions.B3PW91/6-31G density functional calculations were performed on the equilibrium structure, electronic energy gaps and net atomic charges distribution of Ar@C₆₀ cage (atom Ar is set at the center of C₆₀). Equilibrium structures of Ar@C₆₀ and C₆₀ were compared. The same level of calculations were performed mainly on the potential energy curves (PECs) of Ar@C₆₀ cage in its different independent directions [classified in symmetrical point groups: (1) D_2h (2) D_3d (3) D_5d (4) C_2h(2) and (5) C_2h(1)]. Displacements both on elongation and compression were realized by modification of redundant coordinates in the five directions. Close to equilibrium structure, the over-all elastic (force) constants k are calculated and the PECs are accurately fitted to polynomials analytically for large structure distortions. The results show that, when C₆₀ cage is filled with atom Ar, the structural parameters of the cage do not change obviously, but atom Ar has a small positive charge and each of the atoms C has a even smaller negative electronic density. PECs show that the energies at the structure of the cage closed to be destroyed are: 1) 2966.2 kJ·mol^-1, 2) 5619.2 kJ·mol^-1, 3) 5842.9 kJ·mol^-1, 4) 2054.5 kJ·mol^-1 and 5) 2222.2 kJ·mol^-1, respectively. The over-all elastic...