Density functional method (B3LYP) has been used to optimize the possible structures of PdY and PdYH molecules by contracted valence basis set (SDD) for Pd and Y atoms and the 6-311＋＋G** basis set for H atom. The results show that the ground states of PdY and PdYH molecules are X²Σ^＋ and X¹A' states, respectively. The equilibrium geometry R＝0.24168 nm, dissociation energy D_e＝2.8261 eV, and spectral constants ω_e＝254.0656 and ω_ex_e＝0.60391 cm^－1 of PdY (C_∞v) molecule have been obtained, respectively. For PdYH (C_s) molecule, the equilibrium geometry, dissociation energy and harmonic frequency were calculated, and the results show that R_PdY＝0.24281 nm, R_YH＝0.19824 nm, ∠PdYH＝116.7157° and D_e＝5.6146 eV, and ν₁ (a')＝348.2909 cm^－1, ν₂ (a')＝243.3382 cm^－1, ν₃ (a') ＝1442.2695 cm^－1, respectively. Analytical potential energy function for the PdYH has been derived for the first time using many-body expansion method, which was successfully used for describing the equilibrium geometry of PdYH. Molecular reaction kinetics of Pd(¹S_g)＋Y(²D_g)＋H(²S_g) based on this potential energy function is being studied under way.

Key words: PdY, PdYH, relativistic effective core potential, many-body expansion potential energy function