Investigation on analytic potential energy function of NH_2 radical using coupled-cluster theory in combination with the correlation-consistent basis sets

The coupled-cluster singles-doubles-approximatetriples [CCSD(T)] theory in combination with the series of the correlation-consistent basis sets of Dunning and co-workers are used to calculate the equilibrium geometries of NH2 radical.By careful comparison between the available experiments and the present results,the cc-pV5Z basis set is found to be the most suitable one for further calculations.The values obtained at this basis set are of 0.10247 nm for the equilibrium bond length RN-H,102.947° for the bond angle ∠HNH,4.2845 eV for the dissociation energy De and 1546.0342 cm-1,3379.5543 cm-1 and 3474.4784 cm-1 for the harmonic frequencies ν1(a1),ν2(a1) and ν3(b2),respectively.The equilibrium geometries,harmonic frequencies and potential energy curves of the ground-state NH radical and H2 molecules are calculated at the CCSD(T)/cc-pV6Z level of theory.The ab initio calculation points are fitted to the analytic Murrell-Sorbie function with the least-squares method.The spectroscopic parameters derived from the analytic potential energy functions are in good accord with the available experiments.The analytic potential energy function of the NH2(C2v,X2B1) radical is derived using the many-body expansion theory.This function correctly describes the configuration and dissociation energy of the ground-state NH2 radical.