用耦合簇理论及系列相关一致基研究基态SH+ 和 SD+ 的光谱常数*

利用耦合簇理论CCSD(T)和相关一致基组cc-pVXZ和aug-co-pVXZ(X=2,3,4,5)计算了SH 和SD 的基态平衡几何re、谐振频率ωe和离解能De.计算结果表明,所用基组越大,得到的结果与实验值之间的差别就越小,因此我们选用了大基组aug-cc-pV5Z在0.07～2.50 nm的核间距范围内对SH 和SD 的基态进行单点能计算,并将计算结果拟合成了Murrell-Sorbie函数.利用得到的解析势能函数,计算了SH 和SD 的其余3个光谱常数(ωexe,αe和Be),其结果与实验值符合得相当好.     

基于Ne-HBr从头算CCSD(T)势的散射截面

利用非线性最小二乘法拟合在CCSD(T)/aug-cc-pVQZ理论水平下计算的相互作用能,得到了基态Ne-HBr复合物相互作用势的解析表达式.基于拟合的从头算CCSD(T)势,通过收敛的密耦计算得到了入射能量分别为40,60,80和100 meV时,Ne-HBr散射的微分截面和分波截面,详细讨论了态-态转动激发截面对总非弹性散射截面的影响和散射截面随能量的变化趋势.希望研究结果对该体系的散射实验和进一步的理论研究能提供参考信息.     

LiBr分子基态光谱常数和分子常数研究

采用高精度的量子化学从头计算多参考组态相互作用方法和相关一致基, 计算了LiBr分子基态的光谱常数和势能曲线. 为获得更准确的结果, 计算中还考虑了二阶Douglas-Kroll-Hess相对论修正对LiBr分子基态的平衡键长、谐振频率和离解能影响. 将计算得到的势能曲线拟合为Murrell-Sorbie解析势能函数形式, 并进一步计算得到LiBr分子基态的其它光谱常数,ωeχe, αe, Be, D0. 比较发现它们与实验值符合的非常好. 通过求解核运动径向Schrodinger方程, 找到了LiBr分子基态的全部振动态. 还计算了每一个振动态的振动能级、经典转折点和惯性转动常数, 这些结果与已有的实验值一致.     

POX(X=1,2)的光谱常数与从头算势能曲线

采用从头算的多种方法对PO、PO₂自由基的基态结构进行优化计算,结果表明：使用密度泛函（DFT）方法计算的结果最接近实验值.对PO双原子分子优选6-311G（3df）基组进行计算、扫描并拟合.对PO₂三原子分子优选出6-311+G（3df）方法计算结构参数、谐振频率、离解能及力常数,借助多体项展式理论导出PO₂自由基的势能函数并绘制等值势能图.发现：PO₂自由基的对称伸缩振动和旋转势能图中,在O+PO→OPO反应通道上都有鞍点出现,O原子需要越过0.55 eV的能量才能生成稳定的PO₂自由基.要形成PO₂自由基只能通过两等价的通道越过势垒才能形成.     

LiBr分子基态光谱常数和分子常数研究

采用高精度的量子化学从头计算多参考组态相互作用方法和相关一致基, 计算了LiBr分子基态的光谱常数和势能曲线. 为获得更准确的结果, 计算中还考虑了二阶Douglas-Kroll-Hess相对论修正对LiBr分子基态的平衡键长、谐振频率和离解能影响. 将计算得到的势能曲线拟合为Murrell-Sorbie解析势能函数形式, 并进一步计算得到LiBr分子基态的其它光谱常数,ωeχe, αe, Be, D0. 比较发现它们与实验值符合的非常好. 通过求解核运动径向Schrodinger方程, 找到了LiBr分子基态的全部振动态. 还计算了每一个振动态的振动能级、经典转折点和惯性转动常数, 这些结果与已有的实验值一致.     

用ab initio方法计算NaLi分子基态(X1∑+)的势能函数及光谱常数

运用原子分子群表示方法,首先确定NaLi分子的电子基态(X1∑ ).然后选用6-311 G(3df,2pd)基组优化计算得到NaLi分子基态(X1∑ )的平衡结构和离解能,采用电子相关QCISD(T)方法结合6-311 G(3df,2pd)基组对NaLi分子基态进行单点能扫描计算.最后用单点扫描计算值结合优化计算所得参数去拟合Murrell-Sorbie函数,得到了NaLi分子基态的势能函数.用该势能函数计算的光谱常数与实验结果符合得很好,表明拟合确定的势能函数能精确地描述基态NaLi分子的结构和性质.     

Ne-HBr复合物CCSD(T)势能面对转动非弹性分波截面的影响

利用非线性最小二乘法拟合在CCSD(T)/aug-cc-pVQZ理论水平下计算的相互作用能，得到了基态Ne-HBr复合物势能面的解析表达式.在此基础上，采用量子密耦方法计算了入射能量分别为40，60，80 和100meV时，Ne原子与HBr分子碰撞的分波截面，详细讨论了CCSD(T)势能面的长程吸引和短程各向异性相互作用对非弹性分波截面的影响.结果表明：(1)总非弹性分波截面主要来自j=0 →j′=1, 2跃迁.高J端的尾部极大是势能面长程吸引阱的贡献，主要来自j=0 →j′=1跃迁；低J端的主极大是短程排斥的贡献，主要来自j=0 →j′=2跃迁；极小值是短程排斥和长程吸引作用相互抵消的结果.(2)尽管不同入射能量时非弹性分波截面的峰值和极小值对应的总角动量量子数J各不相同，但它们对应于几乎相同的碰撞参数，取样势能面的相同部分.     

用ab initio方法计算NaLi分子基态（X^1∑^＋）的势能函数及光谱常数

运用原子分子群表示方法，首先确定NaLi分子的电子基态（X^1∑^＋）．然后选用6—311＋＋G（3df，2pd）基组优化计算得到NaLi分子基态（X^1∑^＋）的平衡结构和离解能，采用电子相关QCISD（T）方法结合6—311＋＋G（3df，2pd）基组对NaLi分子基态进行单点能扫描计算．最后用单点扫描计算值结合优化计算所得参数去拟合Murrell—Sorbie函数，得到了NaLi分子基态的势能函数．用该势能函数计算的光谱常数与实验结果符合得很好，表明拟合确定的势能函数能精确地描述基态NaLi分子的结构和性质．     

MRCI方法研究CSe(X1∑+)自由基的光谱常数和分子常数

采用内收缩多参考组态相互作用方法在0.08-2.5 nm的核间距范围内计算了CSe(X1∑+)自由基的势能曲线.为确保势能曲线的计算精度,C原子使用较大的相关一致基aug-cc-pV5Z,Se原子使用最大的相对论赝势基augcc-pV5Z-pp.对CSe(X1∑+)自由基的势能曲线进行了拟合,并进行了同位素识别,得到了该自由基6个主要同位素分子(12C74Se,12C76Se,12C77Se,12C78Se,12C80Se和12C82Se)的光谱常数De,D0,Re,ωe,ωexe,Be和αe,均与已有的实验结果较为一致.利用CSe(X1∑+)自由基的势能曲线,通过求解双原子分子核运动的径向Schr(o)dinger方程并进行同位素识别,找到了J=0时该自由基6个主要同位素分子的全部振动态.针对每一同位素分子的每一振动态,还分别计算了其振动能级、经典转折点和惯性转动常数等分子常数.文中的大部分光谱常数和分子常数属首次报道.     

Ne-Xe体系势能曲线和光谱研究

本论文对Ne-Xe体系的势能曲线和束缚态能级作了系统的研究.采用耦合簇CCSD(T)方法和超分子近似,以及aug-cc-PVXZ(X=T,Q,5)基组,计算了Ne-Xe体系的相互作用势,并采用三种方案外推得到基底限值,给出了不同基底和外推方法下的势能曲线平衡位置和势阱深度.计算了Ne-Xe体系振转能级和各同位素基振动态的纯转动跃迁频率,及相应的光谱常数,并与实验结果进行了比较.     

GeS分子基态和低激发态的势能曲线与光谱性质

本文以aug-cc-pv5Z为基组, 采用考虑Davidson修正的多参考组态相互作用方法(MRCI+Q)得到了GeS分子基态(X¹Σ⁺)和5个低激发态(1¹Σ, 1¹Δ, A¹Π, 1⁵Σ⁺, 2⁵Σ⁺)的势能曲线. 计算结果表明: 2⁵Σ⁺态为排斥态, 其余5个态为束缚态; 6个态有着共同的离解通道, 离解极限均为Ge(³P)+S(³P). 利用计算得到的势能曲线得了X¹Σ⁺, 1¹Σ^-, 1¹Δ, A¹Π和1⁵Σ⁺态的垂直跃迁能T_e, 平衡键长R_e, 离解能D_e, 谐振频率ω_e, 非谐性常数ω_ex_e及平衡位置的电偶极矩. X¹Σ⁺态的R_e 为2.034 Å, D_e 为5.728 eV, ω_e为571.73 cm^-1, ω_ex_e为1.6816 cm^-1, 平衡位置的电偶极矩为1.9593 Debye. 激发态1¹Σ, 1¹Δ, A¹Π, 1⁵Σ⁺的T_e 依次为25904.81, 26209.22, 32601.19, 43770.26 cm^-1; R_e依次为2.313, 2.322, 2.188, 2.8790 Å; D_e依次为2.524, 2.487, 1.694, 0.3036 eV, ω_e依次为358.90, 353.08, 376.32, 134.96 cm^-1; ω_ex_e依次为1.2421, 1.2151, 1.6608, 1.9095 cm^-1; 平衡位置的电偶极矩依次为1.3178, 1.4719, 1.5917, -1.9785 Debye. 通过求解核运动的薛定谔方程得到了J=0时X¹Σ⁺, 1¹Σ^-, 1¹Δ, A¹Π和1⁵Σ⁺态前30个振动态的振动能级G_v和分子常数B_v, 得到的结果和已有的实验值及其他理论值符合较好.     

Spectroscopic and ab initio characterization of the conformational states of the bis(perfluoro‐ ethanesulfonyl)imide anion (BETI−)

Ab initio calculations were combined with infrared and Raman studies to spectroscopically distinguish the two conformers of the BETI⁻ or bis(perfluoroethanesulfonyl)imide anion, [N(SO₂C₂F₅)₂]⁻, as was previously done for [N(SO₂CF₃)₂]⁻, the TFSI⁻ anion. BETI⁻ is predicted to exist, as does TFSI⁻, in two conformational states of C₂ and C₁ symmetries, the former being more stable by about 6 kJ mol⁻¹. This conformational isomerism produces weak Raman splittings that can be resolved only at low temperatures. Thus, solutions of LiBETI with glymes cooled down to 113 K exhibit a very intense Raman doublet at ∼745–740 cm⁻¹ characteristic of a quenched conformational equilibrium between the C₂ and C₁ conformers. Annealing of the (G3)₂:LiBETI solvate, where G3 is triglyme, leads to an ordered crystalline phase with all the anions in the C₂ conformation, as in the reference salt Me₄NBETI. This conclusion cannot be extended to all the systems in which the BETI⁻ anion interacts weakly with the cation, however, since the diglyme solvate, (G2)₂:LiBETI, contains both C₁ and C₂ anion conformers (in 2:1 ratio) at low temperatures independent of the sample's thermal history. The conformational splittings are larger in infrared, as illustrated by two absorption bands at 601 and 615 cm⁻¹ associated with the C₂ and C₁ anion conformers, respectively. It is possible to follow the relative intensities of these bands in a LiBETI solution with diglyme above room temperature up to 387 K. The C₂ conformer is found to be more stable than C₁ by 4.7 ± 0.7 kJ mol⁻¹. Copyright © 2006 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies,conformations and ab initio calculations of 1,2‐bis(trifluorosilyl)ethane (SiF3CH2CH2SiF3)

Infrared spectra of 1,2‐bis(trifluorosilyl)ethane (SiF₃CH₂CH₂SiF₃) were obtained in the vapour and liquid phases, in argon matrices and in the solid phase. Raman spectra of the compound as a liquid were recorded at various temperatures between 293 and 270 K and spectra of an apparently crystalline solid were observed. The spectra revealed the existence of two conformers (anti and gauche) in the vapour, liquid and in the matrix. When the vapour was chock‐frozen on a cold finger at 78 K and annealed to 150 K, certain weak Raman bands vanished in the crystal. The vibrational spectra of the crystal demonstrated mutual exclusion between IR and Raman bands in accordance with C_2h symmetry. Intensity variations between 293 and 270 K of pairs of various Raman bands gave ΔH(gauche—anti) = 5.6 ± 0.5 kJ mol⁻¹ in the liquid, suggesting 85% anti and 15% gauche in equilibrium at room temperature. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices, is the low‐energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted, and 34 anti and 17 gauche bands were tentatively identified. Ab initio and density functional theory (DFT) calculations were performed giving optimized geometries, infrared and Raman intensities and anharmonic vibrational frequencies for both conformers. The conformational energy difference derived in CBS‐QB3 and in G3 calculations was 5 kJ mol⁻¹. Copyright © 2009 John Wiley & Sons, Ltd.     

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     

Concentrated Fe(III)–nitrilotriacetate solutions: study by Raman spectroscopy and ab initio calculations

Fe(III)–nitrilotriacetate(NTA) aqueous solutions are used in various redox desulfurization processes. The nature of stable Fe–NTA complexes depends highly on parameters such as [Fe(III)] concentration, NTA/Fe ratio and pH value. These complexes can be characterized by potentiometric measurements or UV‐vis spectroscopy, but only at rather low concentrations. Using synthesis of solids, Raman spectra of these solids and ab initio calculations, a rational determination of the nature of complexes stable in water at high iron concentrations was proposed from the position sensitivity of the main low wavenumber band to the coordination sphere of iron cations. This band was assigned to ν(Fe N) stretching vibrations from ab initio calculations. Depending on the pH and NTA/Fe ratio of the prepared solutions, different species were identified from the Raman spectra. The present methodology can be extended to other metal–ligand systems to elucidate the nature of stable complexes in aqueous solution. Copyright © 2006 John Wiley & Sons, Ltd.     

Gaussian basis set of triple zeta valence quality for the atoms from K to Kr: Application in DFT and CCSD(T) calculations of molecular properties

A contracted basis set of triple zeta (TZ) valence quality for the atoms from K to Kr was constructed from fully-optimized Gaussian basis sets generated in this work. Gaussian polarization functions (d, f, and g symmetries), which were optimized at the second-order Mφller–Plesset level, were added to the TZ set. This extends earlier work on segmented contracted TZ basis set for atoms H-Ar. This set along with the BP86 non-hybrid and B3LYP hybrid functionals were used to calculate geometric parameters, dissociation energy, harmonic vibrational frequency, and electric dipole moment of a sample of molecules and, then, comparison with results obtained with other basis sets and with experimental data reported in the literature is done. CCSD(T) atomic excitation energies and bond lengths, dissociation energies, and harmonic vibrational frequencies of some diatomics were also evaluated. Using density functional theory and gauge-including atomic orbitals, ⁵⁷Fe and ⁷⁷Se nuclear magnetic resonance chemical shifts in Fe(C₅H₅)₂, H₂Se, (CH₃)SeH, CSe₂, SeCO, H₂CSe, and SeF₆ were calculated. Comparison with theoretical and experimental values previously published in the literature was done. It is verified that in general these results give good agreement with experimental and benchmark values.     

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.