Theoretical Investigations On The Spectroscopic Properties For Some Low-lying Electronic States Of NCl And NH Molecules

Potential energy function (PEF) is a comprehensive description of molecular electronic states under the Born-Oppenheimer approximation, which, on the other hand, reflects the mechanic properties,geometrical properties and spectroscopic properties. The potential energy functions of diatomic molecules and radicals are fundamental for the reason that the only variable in this function is the internuclear distance. Therefore, it is the best way for further study of molecular spectroscopy, molecular reaction dynamics as well as atomic and molecular collision to better know the PEFs of diatomic molecules.On the other hand, it is also important how we obtain the analytical forms of potential energy functions to ensure the accuracy of spectroscopic constants. In this paper, the complete active space self-consistent field (CASSCF) method was adopted to provide optimal orbit for the subsequent calculation and the internally contracted multi-reference configuration interaction (icMRCI) calculations were then carried out at the level of correlation consistent basis set AV6Z. With the method above, the potential energy curves (PECs) of NCI (22 ?-S) as well as NH (12 ?-S) radicals were finally plotted. To maintain the accuracy of spectroscopic constants in the present work, various corrections were counted in, including the Davidson modification, core-valence correlation correction and scalar relativistic corrections as well.Notably, the total potential energy was extrapolated to the level of complete basis set (CBS) limit which avoided the basis set truncation errors. To obtain the fine structure spectra of NCI and NH radicals, we included spin orbit coupling effect in our calculations using the Breit-Pauli operator. As a result, the potential energy curves of NCI radical split into 51 while that of NH radical turned into 25. All the spectroscopic constants (De, Te, Re, ?e, ?exe, ?eye, Be and ?e) for the bound states of NCl and NH radicals were predicted by solving the rovibrational Schrodinger equation with Numerov's method. Finally, we evaluated the radiative lifetimes of several transitions (b1?0+-X3?0+-,a1 ?2-X3?0+-, 11?1-X3?0+-,13?1-X3?0+-,13?1+-X3?0+-, 23?0--X3?0+-and 23-?0+--X3?0-+) of NCl as well as A3?-X3?-, c1?-a1?, 23? -X3?-and 23?-A3?of NH radical by their potential energy curves and the corresponding dipole moments.Overall, most of the investigations on the low-lying states involved in this paper are original and newly carried out. With all possible corrections included, the theoretical results in this paper show excellent agreement with that of the available theoretical calculations and experiment measurement. Thus our work would serve both theoretical calculations and experiment researches in the future.