Coupled-cluster single-double theory study on the analytic potential energy function of the SeN2 radicals

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The coupled-cluster single-double (CCSD) theory in combination with the quadruple correlation-consistent basis set (cc-pVQZ) of Dunning and co-workers is employed to estimate the equilibrium geometry, dissociation energy and vibrational frequencies of the SeN2 radical. The computational results show that the ground state of SeN2 has C2v symmetry and its ground electronic state is X1A1. The equilibrium parameters of the structure are RSe-N=0.1691 nm, RN-N=0.1970 nm, αN-Se-N =71.289°, and the dissociation energy is De=4.78 eV. The vibrational frequencies are ν1=326.9288 cm-1, ν2=808.0161 cm-1, and ν3=948.3430 cm-1, respectively. The whole potential curves for the ground electronic states of SeN and N2 are further scanned using the above method, the potential energy functions and relevant spectroscopic constants are then obtained by least square fitting to the Murrell-Sorbie function. Compared with other theoretical results and the experimental values, our computational results are very accurate. Then the analytic potential energy function of SeN2 is derived by many-body expansion theory. The potential curves correctly describe the configurations and the dissociation energy for the SeN2 radical.