Study On Spectral Characteristics For C₂^- And CP⁺

The carbon elements widely distribute in the nature. Carbon-containing compound is the main component of fossil fuels and atmospheric greenhouse gases. In addition, it is present in interstellar space. So the studies of structure and spectral properties of carbide molecules play a very important role in materials science, astronomy, combustion, and environmental fields. However, experimental studies on C₂^- anion and CP⁺ cation are poor, and theoretical data are also not complete.In this paper, these C₂^- and CP⁺ are studied based on the quantum chemistry ab initio calculation principles. The wavefunctions of the valence electrons are optimized by the state-averaged Complete Active Space Self-Consistent Field?CASSCF? method after the Hartree�Fock calculation. Subsequently, the wavefunctions of CASSCF are used in the internally contracted MRCI in combination of the correlation-consistent basis set at the level of AV5 Z. Then, the potential energy curves of X²?+ g, A²?_u, B²?+ u, 4?+ g, 4?_u and 4?+ u six low-lying excited electronic states of C₂^- anion in the separation from 0.8 to 5.0 ? and the 1,3?, 1?+, 3?- and 1? five low-lying excited electronic states of CP⁺ cation are calculated with same way in the separation from 0.8 to 5.0 ? are obtained including Davidson correction, core-valence correlation and scalar relativistic effect. LEVEL program is used to solve the radial Schr?dinger equation of molecular system to obtain the corresponding vibrational energy levels and Franck-Condon?F-C? factor. Then, the corresponding spectral parameters of C₂^- anion and CP⁺ cation are determined by least squares fitting. We also use the Breit-Pauli operator to calculate the spin-orbit coupling splitting curves and spin-orbit coupling constant of A²?_u state of C₂^- anion and 3? and 3?- states of CP⁺ cation. In addition, we also calculated the transition dipole moment?TDM? of A²?_u- X²?+ g state and B²?+ u- X²?+ g state of C₂^- anion and 1?+- 1? state and 3?-- 3? state of CP⁺ cation. Based on the TDMs and the F-C factors, we calculated radiation lives of A²?_u and B²?+ u states of C₂^- anion 1?+- 1? and 3?--3? states of CP⁺ cation, and oscillator strength of B²?+ u state of C₂^- anion.In this paper, these values of spectroscopic constants, radiative lifetimes and oscillator strength well agree with experimental results. Furthermore, there is a high barrier on the potential well of 4?_u state of C₂^- anion. We speculated that this may be caused by avoiding to intersect with a higher symmetry of the same spin states. The spin-orbit coupling constants of A²?_u state of C₂^- anion perfected the theories spectroscopic data, and also very close to the experimental value. The results of CP⁺ cation are in agreement with the theoretical spectroscopic data, and also close to the experimental value. Our results may provide some reference data for the experimental measurements.