Abstract: Density functional(B3LYP) method has been used to optimize the possible structures of PdH2 and YH2 molecules by contracted valence basis set(SDD) for Pd and Y atoms, the 6-311＋＋G** basis set for H atom. The results show that the ground state of PdH2 molecule is C2v symmetry and X 1A1 state. The parameters of structure and the harmonic frequencies are RPdH=0.1692 nm, ∠HPdH=29.4°, De=5.5212 eV and ν1=1470.1 cm－1,ν2=1007.9 cm－1,ν3=2907.0 cm－1 respectively. The results also show that the ground state of YH2 molecule is C2v symmetry and X 2A1 state. The parameters of structure and the harmonic frequencies are RYH=0.1962 nm,∠HYH=114.3°, De=5.6691 eV and ν1=1457.9 cm－1,ν2=475.9 cm－1,ν3=1506.3 cm－1 respectively. The potential energy functions of PdH2 and YH2 have been derived from the normal equation fitting and the many-body expansion theory which is successfully used for describing the equilibrium geometry of PdH2 and YH2.Molecular reaction kinetics of Pd ＋ H2 and Y ＋ H2 based on this potential energy function is discussed briefly.

Key words: PdH2, YH2, Molecular structure, Potential energy function