Analytic potential energy function of the SiH2(C2v, X1A1) radical using CCSD(T) theory in combination with quintuple correlation-consistent basis set

The coupled-cluster single-double withy a perturbative triple excitations CCSDT 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 SiH2C2v, 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 DeHSi—H and 1020.0095, 2074.8742　 and 2076.4762 cm-1 for the vibrational frequencies ν1a1, ν2a1 and ν3a1, respectively. The equilibrium geometry, harmonic frequency and potential energy curve of the SiHX2Π radical are calculated at the CCSDT/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 SiH2C2v, X1A1 radical is derived by using the many-body expansion theory. This function correctly describes the configuration and dissociation energy of the SiH2C2v, 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.