The coupled-cluster single-double withy a perturbative triple excitations ［CCSD（T）］ theory in combination with the quintuple correlation-consistent basis set （cc-pV5Z） of Dunning and co-workers is employed to determine the equilibrium geometry, dissociation energy and vibrational frequencies of the SiH2（C2v, X1A1） radical. By comparison, excellent agreement can be found between the present results and the experiments. The values obtained at cc-pV5Z are 0.15163 nm for the equilibrium bond length RSi—H, 92.363° for the bond angle α of H—Si—H, 3.2735 eV for the dissociation energy De（HSi—H） and 1020.0095, 2074.8742 and 2076.4762 cm-1 for the vibrational frequencies ν1（a1）, ν2（a1） and ν3（a1）, respectively. The equilibrium geometry, harmonic frequency and potential energy curve of the SiH（X2Π） radical are calculated at the CCSD（T）/aug-cc-pV5Z level of theory. The ab initio points are fitted to the Murrell-Sorbie function with the least-squares method. The spectroscopic parameters, whether directly determined by the Gaussian03 program package or they are derived from the analytic potential energy function， conform almost perfectly with the available experimental results. The analytic potential energy function of the SiH2（C2v, X1A1） radical is derived by using the many-body expansion theory. This function correctly describes the configuration and dissociation energy of the SiH2（C2v, X1A1） radical. Two symmetrical saddle points have been found at （0.312, 0.160 nm） and （0.160, 0.312 nm）, respectively. And the barrier height is found to be 0.5084 eV.
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