Structural, Spectroscopic and Vibrational Properties for Low-Lying Electronic States of LiCl

A multireference configuration interaction(MRCI) study has been carried out on the LiCl molecule. The potential energy has been calculated over a wide range of internuclear separation for the 21 low-lying electronic states of the LiCl molecule dissociating into Li(2S,2P,3S)+Cl(2P). The(4)1Σ+,(3)1Π, 1-33Σ+, 1-33Π,1,3,1,3Σ,(5)1Σ+,(4)3Σ+,(4)1Π,(4)3Π excited states are studied for the first time in theory. Molecular spectroscopic constants(Re, De,ωe, ωeχe, Be and αe) have been derived for the 9 bound states(X1Σ+,(3)1Σ+,(2)3Σ+,1,3,1,3Σ,(4)1Π,(4)3Π) with a regular shape, and the spectroscopic constants of ground states X1Σ+are in good agreement with available experimental and theoretical values. The relative diferences between experimental values and our values for Re, De, ωe, ωeχe, Be andαe are 1.02%, 0.60%, 1.72%, 9.46%, 2.0%, and 0.75%, respectively. Moreover, vibrational levels of 9 bound states, which have not been investigated experimentally, are computed.     

Potential energy curves and spectroscopic properties of X2∑ and A2П states of 13C14N

The potential energy curves(PECs) of X2+Σand A2Π states of the CN molecule have been calculated with the multireference configuration interaction method and the aug-cc-pwCV5Z basis set. Based on the PECs, all of the vibrational and rotational levels of the13C14N molecule are obtained by solving the Schro¨dinger equation of the molecular nuclear motion.The spectroscopic parameters are determined by fitting the Dunham coefficients with the levels. Both the levels and the spectroscopic parameters are in good qualitative agreement with the experimental data available. The analytical potential energy functions are also deduced from the calculated PECs. The present results can provide a helpful reference for future spectroscopy experiments or dynamical calculations of the molecule.     

LiAl分子基态、激发态势能曲线和振动能级

利用单双激发多参考组态相互作用方法获得了LiAl分子基态X¹∑⁺及七个激发态a³∏, A¹∏, b³∑⁺, c³∑⁺, B¹∏, C¹∑⁺, d³∏的势能曲线, 通过势能曲线得到各态的平衡核间距R_e, 进而求得绝热激发能和垂直激发能.计算结果表明:c³∑⁺ 电子态是一个不稳定的排斥态, A¹∏态是一个较弱的束缚态, 其余6个电子态均为束缚态; b³∑⁺与 c³∑⁺态之间存在预解离现象; 8个电子态分别解离到两个通道, 即Li(²S)+Al(²P⁰)与Li(²P⁰)+Al(²P⁰). 接着将势能曲线拟合到Murrel-Sorbie解析势能函数形式, 据此获得各态的光谱数据:基态X¹∑⁺的平衡键长为0.2863 nm, 谐振频率为316 cm^-1, 解离能D_e为1.03 eV, 激发态a³∏, A¹∏, b³∑⁺, c³∑⁺, B¹∏, C¹∑⁺, d³∏的垂直激发能依次为0.27, 0.83, 1.18, 1.14, 1.62, 1.81, 2.00 eV; 解离能依次为1.03, 0.82, 0.26, 排斥态, 1.54, 1.10, 0.93 eV, 相应谐振频率 ω_e为339, 237, 394, 排斥态, 429, 192, 178 cm^-1. 通过求解核运动的薛定谔方程找到了J=0时 LiAl分子7个束缚电子态的振动能级和转动惯量. 关键词： LiAl 光谱常数 势能曲线 振动能级     

Ab initio study of ground and low-lying excited states of MgLi and MgLi+ molecules with valence full configuration interaction and MRCI method

The ground and low-lying excited states of MgLi and MgLi⁺ molecules have been investigated. The potential energy curves and the permanent and transition dipole moments of the MgLi and MgLi⁺ molecules are determined making use of the multi-reference configuration interaction and valence full configuration interaction with large basis sets. The core–valence correlation and scalar relativistic correction are also taken into account with aug-cc-pCVQZ basis set and the third-order Douglas–Kroll Hamiltonian approximation, respectively. The transition dipole moments are used to evaluate the radiative lifetimes of the vibrational levels for the low-lying excited states of the MgLi and MgLi⁺ molecules. The derived spectroscopic constants of the ground and low-lying excited states are in good agreement with available experimental and theoretical works.     

基于非谐力场的HOI分子振动光谱研究

应用包含非迭代三激发(CCSD(T))、迭代三激发(CC3)及其变体(CCSDT-3)的耦合簇理论(CC)和密度泛函理论(DFT)之B3LYP方法,使用直到五阶的自洽相关一致基组aug-cc-pVxZ/aug-cc-pVxZ-PP(x=T, Q, 5),首先优化出HOI的平衡结构,接着在该结构附近采样势能点并将其在简正坐标下拟合成直到四阶的多项式力场,依据该力场结合振动自洽场(VSCF)、振动组态相互作用(VCI)和二阶振动微扰理论(VPT2)进行非谐振动分析,精确预期了HOI的基频、直到v₁+v₂+v₃=3的和频与倍频,得到其转动常数、旋振相互作用常数、非谐性常数和离心畸变常数,同时振子强度被估计,氘取代效应被进一步考察。结果表明：当前计算值与已知实验结果符合良好,其中耦合簇理论计算的振动光谱常数更加可靠,DFT误差明显偏大,但两者计算的振动频率却相当一致;并非基组越大,计算得到的非谐振动常数/频率与实验更符合,总体来讲CC3和CCSDT-3的结果更值得信赖;HOI/DOI都没有共振发生。     

SF分子基态及低激发态势能函数与光谱常数的研究

采用含Davidson修正的内收缩多参考组态相互作用的方法和考虑相对论修正, 在价态范围内的最大相关一致基 aug-cc-pV6Z 的条件下, 对SF分子的基态²∏及几个低激发态⁴∑^-, ²∑^-, ²Δ进行了势能扫描计算. 对SF分子的势能曲线进行拟合, 得到了该分子的光谱常数R_e, ω_e, ω_eχ_e, D₀, D_e, B_e和 α_e, 通过比较发现它们与已有的实验结果较为一致. 利用SF分子的势能曲线, 通过求解双原子分子核运动的径向Schrödinger方程得到J=0 时SF分子所计算各电子态的多个振动态. 对于每一振动态, 分别计算了振动能级、惯性转动常数和离心畸变常数. 关键词： SF 势能曲线 光谱常数 分子常数     

Spectroscopic investigations on NO＋（X1∑＋, a3∑＋, A1II） ion using multi-reference configuration interaction method and correlation-consistent sextuple basis set augmented with diffuse functions

Three low-lying electronic states （X1∑, a3∑＋, and A1II） of NO＋ ion are studied using the complete active space self-consistent-field （CASSCF） method followed by highly accurate valence internally contracted multi-reference configuration interaction （MRCI） approach in combination of the correlation-consistent sextuple basis set augmented with diffuse functions, aug-cc-pV6Z. The potential energy curves （PECs） of the NO＋（X1∑＋, a3∑＋, A1II） are calculated. Based on the PECs, the spectroscopic parameters Re, De, We, WeXe, ae, Be, and D0 are reproduced, which are in excellent agreement with the available measurements. By numerically solving the radial SchrSdinger equation of nuclear motion using the Numerov method, the first 20 vibrational levels, inertial rotation and centrifugal distortion constants of NO＋（X1∑＋, a3∑＋, A1II） ion are derived when the rotational quantum number J is equal to zero （J = 0） for the first time, which accord well with the available measurements. Finally, the analytical potential energy functions of these states are fitted, which are used to accurately derive the first 20 classical turning points when J = 0. These results are compared in detail with those of previous investigations reported in the literature.     

Configuration interaction studies on the spectroscopic properties of PbO including spin-orbit coupling

Lead oxide(Pb O), which plays the key roles in a range of research fields, has received a great deal of attention. Owing to the large density of electronic states and heavy atom Pb including in Pb O, the excited states of the molecule have not been well studied. In this work, high level multireference configuration interaction calculations on the low-lying states of Pb O have been carried out by utilizing the relativistic effective core potential. The effects of the core-valence correlation correction, the Davidson modification, and the spin–orbital coupling on the electronic structure of the Pb O molecule are estimated. The potential energy curves of 18 Λ-S states correlated to the lowest dissociation limit(Pb(~3P_g) + O(~3P_g)) are reported. The calculated spectroscopic parameters of the electronic states below 30000 cm~(-1), for instance, X~1Σ~+, 1~3Σ~+,and 1~3Σ~-, and their spin–orbit coupling interaction, are compared with the experimental results, and good agreements are derived. The dipole moments of the 18 Λ-S states are computed with the configuration interaction method, and the calculated dipole moments of X~1Σ~+and 1~3Σ~+are consistent with the previous experimental results. The transition dipole moments from 1~1Π, 2~1Π, and 2~Σ to X~1Σ~+and other singlet excited states are estimated. The radiative lifetime of several low-lying vibrational levels of 1~1Π, 2~1Π, and 2~1Σ~+ states are evaluated.     

AsCl自由基的基态及激发态的势能函数与光谱常数的研究

利用原子分子反应静力学推导出AsCl自由基的基态及激发态的理解极限. 采用完全活性空间自洽场和含Davidson 修正的内收缩多参考组态相互作用理论方法, 在aug-cc-pV5Z基组下对AsCl自由基进行结构优化计算及单点能扫描计算. 在AsCl自由基基态势能曲线的基础上, 通过Molcas程序拟合出了AsCl的光谱常数D_e, R_e, ω_e, ω_eχ_e, B_e 和α_e. 通过求解双原子分子核运动的径向Schrödinger方程, 找到了J=0 时该分子基态存在的40个振动态. 针对每一振动态, 计算了其振动能级、转动惯量B_ν和离心畸变常数D_ν, 与现有的实验及其他理论相比较, 本文的光谱参数和分子常数结果更准确. 关键词： AsCl 势能函数 光谱常数     

GeO分子激发态的电子结构和跃迁性质的组态相互作用方法研究

应用多参考组态相互作用方法计算了GeO分子的第一解离极限(Ge(³P_g)+O(³P_g))对应的18个Λ-S电子态的电子结构. 计算中纳入了Ge原子的3d轨道电子的内壳层-价壳层电子关联效应、标量相对论效应和Davidson修正. 基于计算的电子态的电子结构, 通过求解径向Schrödinger方程获得了束缚电子态的光谱常数R_e, T_e, ω_e, ω_eχ_e, B_e, 理论计算给出的这些电子态的光谱常数与之前的实验结果符合得很好. 计算了电子态的电偶极矩随核间距的变化, 分析了电子态的组态成分的变化对电偶极矩的影响. 计算的势能曲线表明, 激发态A¹Π, 1¹Σ^-, D¹Δ, a³Π, a’³Σ⁺, d³Δ 和 e³Σ^-的绝热激发能密集地分布于26000-37000 cm^-1范围内, 这些密集分布的电子态之间的相互作用对振动波函数有明显扰动作用. 借助于激发态之间的自旋-轨道耦合矩阵元, 阐明了邻近的激发态对A¹Π和a³Π的扰动作用. 基于计算的A¹Π-X¹Σ⁺和A’¹Σ⁺-X¹Σ⁺跃迁的电偶极跃迁矩和Franck-Condon 因子, 给出了A¹Π 和A’¹Σ⁺态的最低的六个振动能级的辐射寿命.     

Multireference configuration interaction potential curve and analytical potential energy function of the ground and low-lying excited states of CdSe

The potential energy curves (PECs) of the ground state ($^{3}\Pi )$ and three low-lying excited states ($^{1}\Sigma $, $^{3}\Sigma $,$^{ 1}\Pi )$ of CdSe dimer have been studied by employing quasirelativistic effective core potentials on the basis of the complete active space self-consistent field method followed by multireference configuration interaction calculation. The four PECs are fitted to analytical potential energy functions using the Murrel--Sorbie potential function. Based on the PECs, the vibrational levels of the four states are determined by solving the Schr\"{o}dinger equation of nuclear motion, and corresponding spectroscopic constants are accurately calculated. The equilibrium positions as well as the spectroscopic constants and the vibrational levels are reported. By our analysis, the $^{3}\Pi $ state, of which the dissociation asymptote is Cd($^{1}$S) + Se($^{3}$P), is identified as a ground state of CdSe dimer, and the corresponding dissociation energy is estimated to be 0.39\,eV. However, the first excited state is only 1132.49\,cm$^{ - 1}$ above the ground state and the $^{3}\Sigma $ state is the highest in the four calculated states.     

An ab initio investigation of the low-lying electronic states of BeH

Potential energy curves(PECs) for the ground state(X 2 Σ +) and the four excited electronic states(A 2 Π,B 2 Π,C 2 Σ +,4 Π) of a BeH molecule are calculated using the multi-configuration reference single and double excited configuration interaction(MRCI) approach in combination with the aug-cc-pVTZ basis sets.The calculation covers the internuclear distance ranging from 0.07 nm to 0.70 nm,and the equilibrium bond length R e and the vertical excited energy T e are determined directly.It is evident that the X2Σ+,A2Π,B2Π,C2Σ+ states are bound and 4Π is a repulsive excited state.With the potentials,all of the vibrational levels and inertial rotation constants are predicted when the rotational quantum number J is set to be equal to zero(J = 0) by numerically solving the radial Schr¨odinger equation of nuclear motion.Then the spectroscopic data are obtained including the rotation coupling constant ω e,the anharmonic constant ωexe,the equilibrium rotation constant Be,and the vibration-rotation coupling constant αe.These values are compared with the theoretical and experimental results currently available,showing that they are in agreement with each other.     

Investigation of the electronic structure of Be2+He and Be+He,and static dipole polarisabilities of the helium atom

The potential energy and spectroscopic constants of the ground and many excited states of the Be⁺He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be²⁺ core and the electron-He interactions by effective potentials. Furthermore, the core–core interactions are incorporated. This permits the reduction of the number of active electrons of the Be⁺He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin–orbit interaction. The core–core interaction for Be²⁺He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be⁺He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole moment has been determined for a large and dense grid of internuclear distances including the spin orbit effect. In addition, a vibrational spacing analysis for the Be²⁺He and Be⁺He ground states is performed to extract the He atomic polarisability.     

Vibronic spectra of aluminium monochloride relevant to circumstellar molecule

The A^1Π→ X^1Σ^+ transition system of aluminium monochloride is determined by using ab initio quantum chemistry.Based on the multi-reference configuration interaction method in conjugate to the Davidson correction(MRCI + Q), the potential energy curves(PECs) of the three electronic states are obtained. Transition dipole moments(TDMs) and the vibrational energy levels are studied by employing the aug-cc-pwCV5Z-DK basis set with 4220-active space. The rovibrational constants are first determined from the analytic potential by solving the rovibrational Schr ¨odinger equation, and then the spectroscopic constants are determined by fitting the vibrational levels, and these values are well consistent with the experimental data. The effect of spin–orbit coupling(SOC) on the spectra and vibrational properties are evaluated.The results show that the SOC effect has almost no influence on the spectroscopic constants of AlCl molecules. For the A^1Π→ X^1Σ^+transition, the highly diagonalized Frank–Condon factor(FCF) is f(00)=0.9988. Additionally, Einstein coefficients and radiative lifetimes are studied, where the vibrational bands include ν'= 0–19→ν'=0–9. The ro-vibrational intensity is calculated at a temperature of 296 K, which can have certain astrophysical applications. At present, there is no report on the calculation of Al Cl ro-vibrational intensity, so we hope that our results will be useful in analyzing the interstellar Al Cl based on the absorption from A^1Π→ X^1Σ^+.     

Ab initio calculation of the ground and first excited states of the lithium dimer

Based on a high level ab initio calculation which is carried out with the multireference configuration interaction method under the aug-cc-pVXZ (AVXZ) basis sets, X=T, Q, 5, the accurate potential energy curves (PECs) of the ground state ${\rm{X}}{}^{{\rm{1}}}{\rm{\Sigma }}_{g}^{+}$ and the first excited state ${\rm{A}}{}^{{\rm{1}}}{\rm{\Sigma }}_{u}^{+}$ of Li₂ are constructed. By fitting the ab initio potential energy points with the Murrell–Sorbie potential function, the analytic potential energy functions (APEFs) are obtained. The molecular bond length at the equilibrium (R_e), the potential well depth (D_e), and the spectroscopic constants (B_e, ω_e, α_e, and ω_eχ_e) for the ${\rm{X}}{}^{{\rm{1}}}{\rm{\Sigma }}_{g}^{+}$ state and the ${\rm{A}}{}^{{\rm{1}}}{\rm{\Sigma }}_{u}^{+}$ state are deduced from the APEFs. The vibrational energy levels of the two electronic states are obtained by solving the time-independent Schrödinger equation with the Fourier grid Hamiltonian method. All the spectroscopic constants and the vibrational levels agree well with the experimental results. The Franck–Condon factors (FCFs) corresponding to the transitions from the vibrational level (v′=0) of the ground state to the vibrational levels (v″=0–74) of the first excited state have been calculated. The FCF for the vibronic transition of ${\rm{A}}{}^{{\rm{1}}}{\rm{\Sigma }}_{u}^{+}$(v″=0) ←${\rm{X}}{}^{{\rm{1}}}{\rm{\Sigma }}_{g}^{+}$(v′=0) is the strongest. These PECs and corresponding spectroscopic constants provide reliable theoretical references to both the spectroscopic and the molecular dynamic studies of the Li₂ dimer.     

AlH~+离子5个Λ-S态和10个?态的光谱性质以及激光冷却的理论研究

利用考虑Davidson修正的内收缩多参考组态相互作用(icMRCI+Q)方法结合相关一致基组aug-ccpV6Z计算了AlH~+离子前两个离解极限对应的5个Λ-S态和10个?态的势能曲线.为了提高势能曲线的可靠性和精确性,计算中考虑了自旋轨道耦合效应、芯电子价电子相关和标量相对论修正以及将势能外推至完全基组极限.基于得到的势能曲线,获得了束缚和准束缚的4个Λ-S态和8个?态的光谱常数和振动能级,与已有的实验结果符合.计算了2(1/2)→X~2Σ_(1/2)~+和A~2Π_(3/2)→X~2Σ_(1/2)~+跃迁的跃迁偶极距.利用计算的精确的势能曲线和跃迁偶极矩,获得了2(1/2)~(第一势阱)(υ′=0, 1)→X~2Σ_(1/2)~+(υ′′)和A~2Π_(3/2)(υ′=0, 1)→X~2Σ_(1/2)~+(υ′′)跃迁的高度对角化分布的Franck-Condon因子(f_(00)和f_(11))和大的振动分支比;预测了2(1/2)~(第一势阱)(υ′=0, 1)和A~2Π_(3/2)(υ′=0, 1)态短的自发辐射寿命和窄的辐射宽度,这适合于AlH~+离子的快速激光致冷.所需的3束激光冷却波长都在紫外区域.这些结果表明了激光冷却AlH~+离子的可行性.此外,评估了自旋轨道耦合效应对光谱常数、振动能级和激光冷却AlH~+离子的影响.     

激光冷却OH分子的理论研究

采用高精度的多参考组态相互作用方法计算OH分子基态和第一激发态的势能曲线.为获得更精确的计算结果,在计算过程中考虑Davidson修正、标量相对论效应、核价相关效应和自旋轨道耦合效应.基于计算的Λ-S和?态的势能曲线,对一维径向薛定谔方程进行数值求解,得到各个电子态的光谱数据,与已报道的实验值和理论值相符合.获得OH分子的永久偶极矩、跃迁偶极矩、振动能级、Franck-Condon因子及辐射寿命,结果表明,A~2Σ~+→X~2Π跃迁具有高度对角化的Franck-Condon因子(0.9053)和短的辐射寿命(5.8363×10~(-7)s),符合激光冷却分子的条件.制定了激光冷却OH分子的具体方案,计算得到激光冷却跃迁A~2Σ~+→X~2Π所需的三束激光波长,主光束波长为307.1532 nm,两束重抽运激光波长为344.9163和349.7659 nm.计算结果为超冷OH分子的实验制备提供重要的理论依据.     

Ne-HCN体系v_3正则模下红外谱的理论研究

本文采用单双迭代耦合簇理论CCSD(T)方法,采用扩展的相关一致基组aug-cc-p VQZ以及中心键函数(3s3p2d2f1g),对Ne-HCN体系三维势能面和对应于HCN反对称伸缩振动(v_3正则模)下的红外谱进行了理论研究.在保持HCN分子质心不变的情况下,通过将对应不同正则坐标Q_3值的七个二维势能面进行六阶多项式插值可以得到Ne-HCN体系三维势能面.在振动绝热近似下,利用三维势V(Qi3,R,θ)计算得到体系基态v_3=0和第一激发态v_3=1两个振动平均势并用其计算了对应的振动能级.每个绝热势均有两个极小值分别对应于线性(全局极小)和近T型构型(局域极小).基态的全局极小值位于R=8.04 a0,阱深为-60.99 cm-1,第一激发态的全局极小值位于R=8.08 a0,阱深为-59.94 cm-1.在HCN分子v_3模式下,计算得到了104条红外谱线,并对该模式下的红外光谱常数进行预测.     

Ab initio configuration interaction study of the ground and low-lying excited states of ZnCd

The multi-reference configuration interaction (MRCI) electronic energy calculations have been carried out on the ground state (X1∑) as well as three low-lying excited states (3∑, 1∏, 3∏) of ZnCd dimer. Potential energy curves (PECs) are therefore generated and fitted to the analytical potential energy functions (APEFs) using the Murrel-Sorbie(MS) potential function. Based on the PECs, the vibrational levels of each state are determined by solving Schr(o)dinger equation of nuclear motion, and corresponding spectroscopic parameters are accurately calculated using the APEFs. The present values of spectroscopic parameters including equilibrium positions and dissociation energies areompared with other theoretical reports available at present.     

多参考组态相互作用方法研究ZnHg低激发态(1∏，3∏)的势能曲线和解析势能函数

采用多参考组态相互作用方法计算了ZnHg二聚体两个低激发∏态(¹∏，³∏)的原子间相互作用势能曲线. 用Murrel-Sorbie函数拟合得到了相应的解析势能函数，并用其计算力常数，进而确定了光谱常数. 所得结果与仅有的理论工作进行了比较. 基于所得势能曲线，通过解分子中原子核运动的薛定谔方程预测了各电子态的振动能级. 关键词： 势能曲线 解析势能函数 光谱常数 振动能级