BeC分子基态和低激发态光谱性质和解析势能函数

BeC是一个具有丰富低激发电子态的分子,本文基于动态权重完全活性空间自冾场方法获得的参考波函数,采用多参考组态相互作用方法对BeC分子进行高精度的从头计算,获得了BeC分子X~3Σ~-,A~3Π,b~1Δ,c~1Π和d~1Σ~+共5个电子态的势能曲线.为了获得精确的光谱结果,在计算中考虑了标量相对论效应修正,并把相互作用能外推至完全基组极限.在此基础上获得了这些态的光谱常数和偶极距,以及一些允许跃迁的跃迁偶极距、弗兰克-康登因子和辐射寿命.最后,通过扩展的Rydberg函数拟合获得了基态势能曲线精确的解析表达式.

Spectroscopic properties and analytical potential energy function of ground and low-lying excited states of BeC moleule

Diatomic molecule BeC has a complex electronic structure with a large number of low-lying excited states that are all strongly bound electronic states. Thus, the BeC molecule has the abundant spectral information. In this work, the potential energy curves and wavefunctions of X³Σ^-, A³Π, b¹Δ, c¹Π and d¹Σ⁺ states of the BeC molecule are calculated by using the internally contracted multi-reference configuration interaction (MRCI) approach, which is based on the use of a dynamically weighted complete active space self-consistent field (DW-CASSCF) procedure. To improve the reliability and accuracy of calculation, the scalar relativistic corrections and the extrapolation of potential energy to the complete basis set limit are taken into account. On the basis of the calculated potential energy curves and wavefunctions, the spectroscopic constants (T_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e, α_e, and D_e) and permanent dipole moments of those states are determined, the results of which are in good agreement with the existing available experimental and theoretical values. The obtained permanent dipole moments indicate that the electrons transfer from Be to C and the polarity for molecule is Be^δ+ C^δ-. The transition properties of the spin-allowed A³Π-X³Σ^-, c¹Π-b¹Δ, c¹Π-d¹Σ⁺ transitions are predicted, including the transition dipole moments, Franck-Condon factors, and radiative lifetimes. The radiative lifetimes for the A³Π-X³Σ^- transitions are predicated to be at a μs level, and the good agreement with previous theoretical values is found. Radiative lifetimes for c¹Π-b¹Δ and c¹Π-d¹Σ⁺ transitions are also evaluated at the levels of μs and ms, respectively. The PEC for the ground state is fitted into accurate analytical potential energy functions by using the extended-Rydberg potential function.