Abstract: Possible ground state structures, harmonic frequency and dissociation energy of SeO_x(x=1,2) free radical are optimized by different methods and base sets included in Gaussian 09. Among them, QCISD(T)/6-311+G(2df) and B3LYP/6-311G(3d2f) are the most suitable for SeO, SeO₂. Calculation results are in good agreement with experiment. For SeO free radical, Murrell-Sorbie potential energy functional constant are calculated, according to which spectral parameters and force constants are shown. It provides basis for further investigation on SeO_x(x=1,2). For SeO₂ free radical, force constants are calculated at the same time. And potential energy functions of SeO₂ are derived with many-body expansion theory. In a symmetric stretching vibration potential energy diagram of SeO₂, saddle points in reaction kinetics O+SeO→SeO₂ in the symmetry dilation potential energy are found. Activation energy is 48.24 kJ·mol^-1. A stable SeO₂ free radical could be formed as O atom with energy surpassing 0.5 eV.

Key words: SeO, SeO₂, spectral constant, potential energy function