7Li20,±1分子体系基态振-转能级的全电子计算

All-electron calculation of ground state vibration-rotation energy levels of 7Li20,±1 molecular systems

采用单参考与多参考耦合簇理论结合相关一致高斯基组计算研究了77Li2(0,±1)分子体系的电子基态的势能曲线,计算考虑了体系所有电子的关联效应与相对论效应,拟合得到了体系的光谱常数,并获得了电子基态的振动-转动能级信息.计算得到的中性与阳离子体系的光谱常数与实验值符合得很好;对于阴离子体系,平衡核间距的计算仍需进一步改进,其他光谱常数符合较好.计算结果表明,中性和阳离子体系基态波函数具有明显的单参考组态特点,而阴离子分子基态应采用多参考组态波函数描述.对于基态的振动-转动能级,与现有实验值符合得很好;尽管各种计算方法对阴离子基态的平衡核间距计算结果仍有差异,但振动能级间隔的结果相互符合得很好.本文的研究可为Li2分子体系基态,尤其是光谱学信息很少的阴离子体系的电子结构与光谱的精确研究提供了有用的光谱信息.

The investigation of spectroscopic information is important for understanding the mechanisms of molecular photochemical and photophysical reactions.As a prototype to study the electronic structures and spectra of diatomic molecular systems,the vibration-rotational spectra of alkali dimer and its ions have aroused considerable research interest in the last two decades.Single-reference and multi-reference coupled cluster theory in combination with correlation consistent Gaussian basis set are adopted to study the ground-state potential energy curves of 7Li2(0,±1)molecular systems.The correlation effect and relativistic effect of all the electrons are taken into account in the calculation.And the spectroscopic constants,including the equilibrium internuclear distance Re,the harmonic vibrational frequency we,the anharmonic constant wexe,the equilibrium rotational constant Be,and the dissociation energy De of the molecular system and vibration-rotational energy level information of the ground states are obtained by solving the radial Schr?dinger equations.The calculated spectroscopic constants of the neutral and positive ion system accord well with the experimental values;however for the negative ion system,the calculation of equilibrium internuclear distance needs further improving,and other spectroscopic constants are consistent well with the experimental values.The present computational results indicate that the ground state wave functions of neutral and positive ion systems have obvious single reference configuration characteristics,while the ground state of negative ion molecule system should be described with multireference configuration wave functions.The vibration-rotational energy levels of ground state with different theoretical methods are in good agreement with the experimental values.The vibrational-rotational energy levels and spectroscopic constants of neutral and positive ion systems are well reproduced,and some experimental information about spectrum is still lacking.Although the difference among the equilibrium internuclear distances for the ground state of the negative ion,obtained from different theoretical methods are still existent,the results of the vibrational level interval accord well with each other.This study provides useful information about spectrum for accurately investigating the electronic structures and spectra of the ground state of Li2 molecular system and its two isotopic molecules,especially for the negative ion system with little information about spectrum.