~7Li_2分子A^1Σ_u^+态的平衡几何、离解能及其谐振频率

The Accurate Equilibrium Internuclear Separation,Dissociation Energy and Harmonic Frequency for the State A^1Σ_u^+ of Dimer ~7Li_2

利用分子反应静力学的原理,确定了7Li2分子A1Σ+态的离解极限;利用SAC-CI方法、使用6-311G、6-311++G、6-311G(3df,3pd)、6-311++G(3df,3pd)、D95(3df,3pd)、D95、D95V、D95V(d,p)、cc-PVTZ和AUG-cc-PVTZ等基组,对7Li2分子A1Σu+态的平衡几何进行了优化计算,且将计算结果与精细的单点能扫描结果进行了比较.分析表明,由单点能扫描获得的平衡核间距应更为合理.同时也得出了AUG-cc-PVTZ基组为最优基组的结论.在0.14~1.5 nm范围内对该态进行了单点能扫描,并用最小二乘法拟合出了其解析势能函数.从得到的解析势能函数出发,计算了该态的力常数(f2、f3和f4)及谐振频率(ωe),进而计算了其他光谱常数(Be,αe和ωeχe),理论值与实验结果一致.同时为便于分析和比较,对基态X1Σg+也进行了相应的计算.

The reasonable dissociation limit of the A^1∑^＋u state of dimer ^7Li2 is attained using the molecular reaction dynamics theory. The geometry optimization of this state is made using a symmetry-adapted-cluster configuration-interaction （SAC-CI） method at such basis sets as 6-311G,6-311 ＋ ＋ G,6-311G（3df,3pd） ,6-311 ＋ ＋ G（3df,3pd）, D95 ,D95 （3df,3pd） ,D95V,D95V（d,p）,cc-PVTZ and AUG-cc-PVTZ in Gaussian03 program package. And the equilibrium internuclear separation comparison is made between the geometry optimization （OPT） results and the fine single-point energy scanning （SPES） ones. The analyses point out that the SPES results are more reasonable than the OPT ones. And the conclusion is gained that the AUG-cc-PVTZ basis set is the most suitable one for the A^1∑^＋u state. The whole potential energy curve is further scanned at the SAC-CI/AUG-cc-PVTZ theory level over a wide internuclear separation range from 0.14 to 1.5 nm,and then has a least squares fitted to the analytic Murrell- Sorbic function form. The force constants （f2、f3 and f4 ） and the harmonic frequency （ωe） of this state is calculated according to the analytic potential energy function. And then other spectroscopy data （B3 ,αe, and ωeХe ） are calculated. It shows that there is an excellent agreement between present calculations and the experimental data about the equilibrium internuclear separation, dissociation energy and the harmonic frequency. At the same time, the corresponding calculations are made for the ground state X^1∑^＋ for convenient comparison.