Electron-vibration approximate method for hydrogen isotope compounds Al2O3X2 (X= H, D, T)

The geometric configurations, vibration frequencies and thermodynamics properties of Al2O3X2 (X= H, D, T) molecular clusters with lower energy are optimized using the B3LYP/6-311++g (d, p) method. The changes of entropy, enthalpy and Gibbs free energy of the reactions between Al2O3 and hydrogen (deuterium or tritium) gas are calculated by the solid electron-vibration approximate method and thermodynamic formulae at temperatures of 298, 398, 498, 598, 698, 798, 898, 998 and 1098 K, and then the relationships between the equilibrium pressure of hydrogen (deuterium or tritium) gas and temperature in these reactions are obtained. The results show that the ground state of the gaseous Al2O3H2 is Al2O3X2 (X= H, D, T) (1A') Cs. Hydrogen can be displaced by deuterium; deuterium can be displaced by tritium in the reactions between Al2O3 and X2 with the productions of solid Al2O3X2 which relates to ground gaseous Al2O3X2 with Cs symmetry. This displacement sequence is opposite to that in the reactions between titanium and X2. These displacement effects are very weak, and they are weaker and weaker as the temperature increases.