Pu-n Pu-oh System, The Molecular Structure And Potential Functions

By using Density functional method B3LYP with SDDRECP constructured for Pu and Gaussian 98 and Gaussian 03, the equilibrium geometric structures and analytical potential energy functions for the plutonium compounds (PuN, PuO, PuH, PuN2 and PuOH) have been computed and studied in this paper. Besides, the thermodynamic functions (between 298.15K and 998.15) for PuOH system have been calculated out by using ab initio method. Moreover, thermodynamic stability of this system has also been analyzed.Firstly, the possible electronic states and the reasonable dissociation limits for plutonium compounds have been derived based on the atomic and molecular reaction statics and the group theoretical derivation of molecular electronic states. Then, the molecular structures for PuN, PuO, PuH, PuN, and PuOH have been optimized by using ab initio method, and the corresponding ground states and geometric structures are PuN(X6∑+, C∞v), PuO(X5∑-, C∞v), PuH(X8 ∑+, C∞v), PuN2 ( X3∑g-, D∞h) and PuOH (X6∑+, C∞v), respectively.The Murrell-Sorbie potential energy functions for the diatomic molecules PuN, PuO and PuH have been obtained according to the ab initio data through the last-square-fitting. The spectroscopic data and force constants for PuN, PuO and PuH have been derived from the potential energy functions. The analytical potential energy function for two structures of 3-atomic molecules (PuN2, PuOH) have also been derived by using many-body expansion method and they all successfully represent the equilibrium structures of ground states for 3-atomic molecules (PuN2, PuOH). Besides, they also describe the geometric structures and energy for the metastable structures of 3-atomic molecules. Moreover, molecular reaction kinetics of two 3-atomic molecules (PuN2, PuOH) based on these potential energy functions has been discussed in this paper.In the last section of this work, based on the RECP for Pu atom and the basis sets 6-311+G* and 6-311++G** for O and H atoms, respectively, the thermodynamic functions (between 298.15 and 998.15) for PuOH(g) molecule have been calculated by using density functional mouthed (B3LYP), and the formed thermodynamic function for PuOH(g) have also been worked out by thermodynamic method. Moreover, we have discussed the thermodynamic stability of PuOH(g) based on these data. Finally, we discussed the corrosion of plutonium in the Pu, O and H system. The results show that the reactions (H(g)+O(g)+Pu(s) â†' PuOH(g), Pu(s)+OH(g) â†' PuOH(g), PuH(g)+O(g)â†'PuOH(g) ) can react spontaneously between the temperature range (298.15 ~ 998.15). However, the reaction PuO(g)+H(g) â†' PuOH(g) can not react spontaneously between the same temperature range. This means that PuOH molecule cannot be formed through the reaction PuO(g)+H(g) â†'PuOH(g) or PuO molecule is so stable in chemical property that it is difficult for PuO molecule to react with H atom gas.