The Study On The Potential Energy Curves Of CN Radical

Quantum Chemical calculation method is one of the most important ways to study the energy level structure and other properties of molecules. It is based on the calculation of the molecular potential energy curves or surfaces whose accuracy depends on the calculation of the correlation energy. It is ideal to expand the wave function to full configuration interaction functions to get the whole correlation energy. But it is impractical because of the too large dimensions resulted from this expansion. So various approximation methods were put out. Among which, multiple reference double excitation configuration-interaction (MRD-CI) method has a good accuracy because it considers all the configurations which have larger contribution to the whole wave function.Transient molecules are short-lived species, which often exist as intermediates of chemical, physical and biological processes. They are the keys for deep understanding of chemical dynamics and molecule structure. CN, as one of the few special and relatively stable free radical, has always been of interest to physicists and chemists, and has been investigated both extensively and intensively.In this thesis, the multireference single and double excitation configuration interaction (MRD-CI) method was employed to calculate the potential energy curves of the ground electronic state X~2∑~+ and the first excited electronic state A~2∏_i of CN. The reference configurations consist of all the configurations which lower the energy at least larger than 0.002Hartree. From the calculation the equilibrium positions of ground state and excited state, as well as the first excitation energy are obtained. We also compare the two calculated potential energy curves with the RKR potential energy curves resulted from the experimental data. They are consistent with each other very well. Consequently, we can expect to get the molecular constants from our results which will be helpful to the experimental work.