CH,NH和OH自由基基态与低激发态分子结构与势能函数

用电子相关耦合簇方法CCSD(T)和aug-cc-pVTZ基函数计算研究了CH, NH和OH自由基分子基态与低激发态的结构与势能函数，导出了分子的光谱数据.结果表明，CH, NH和OH自由基分子基态分别为X²Π，X³Σ和X²Π，基态与低激发态的势能函数均可用Murrell-Sorbie function来表达.CH自由基分子低激发态a⁴Σ^－和⁶Σ^－的绝热 关键词： 电子相关耦合方法 势能函数 结构 自由基     

CH自由基在外电场中的分子结构和势能函数

运用密度泛函B3P86方法,结合Dunning的相关一致五重基cc-PV5Z,获得了CH自由基分子在不同外电场中的键长、偶极矩和振动频率等物理性质参数.通过分析物理性质参数的变化,判断离解电场所处的范围,设置合适的参数扫描该范围的单点能获得势能曲线.结果表明物理性质参数和势能值随外电场的变化而变化,且反向电场中变化幅度较大.利用Morse势模型拟合无外场下势能函数,得到的拟合参数与实验值吻合较好,采用偶极近似构建外电场下的势能函数模型,编制程序拟合对应的势能函数,得出拟合参数,进而计算临界离解电场参量,结果与数值计算值较为一致,说明构建的模型是可靠和准确的.这为分析外场下分子光谱、动力学特性和分子Stark效应冷却囚禁提供重要的理论和实验参考.     

Direct calculation of intermolecular potential energy surfaces

A variation perturbation method is presented for the direct calculation of intermolecular interaction energies. The theory is based on valence bond ideas but avoids the full evaluation of the matrix elements by expansion in powers of interchange, a procedure which is valid for small overlap between the systems. The participating excited states are regarded as polarized pseudo-states and are determined by optimizing the long-range multipole-multipole part of the interaction energy. The validity of these ideas is illustrated by a calculation of the He-He interaction. A remarkable simplification is pointed out, in which the interaction energy is given almost exactly by the sum of the repulsive term, calculated as zero + single interchange, plus the long-range interaction.     

Frequency optimized potential energy functions for the ground-state surfaces of HCN and HCP

Potential energy functions for the ground states of the linear triatomics HCN, HNC ($\text{X}\text{?}{}^1\text{Σ}{}^{\mathrm{+}}$) and HCP ($\text{X}\text{?}{}^1\text{Σ}{}^{\mathrm{+}}$) were derived, by minimizing the difference between the observed vibrational frequencies and those calculated from the potentials by a variational method. Good agreement is obtained between the observed and calculated spectra for HCN and HNC. For the HCP system, a secondary minimum is predicted to lie on the ground-state surface (linear HPC) having dimensions $\text{R}{}_{\mathrm{<mtext>HP</mtext>}}\text{= 1.43}\text{A}\text{?}$, $\text{R}{}_{\mathrm{<mtext>CP</mtext>}}\text{= 1.56}\text{A}\text{?}$, and an energy of 3.8 eV above the HCP ($\text{X}\text{?}{}^1\text{Σ}{}^{\mathrm{+}}$) minimum.     

Calculations of potential energy surfaces in the complex plane

Procedures are developed and tested for the numerical analytic continuation of the difference between two potential energy surfaces of the same symmetry in the vicinity of their complex-valued intersection. Rational fractions are used for curve-fitting ΔE as a function of either one or two independent, complex nuclear coordinates. The rational fractions are constructed from discrete values of ΔE(R, r) to exhibit the branch-point structure explicit in the complex square root function. For analytic continuation to values of the nuclear coordinates with small imaginary parts only real-valued input points are required. In order to analytically continue ΔE farther off the real-axis a few complex-valued input points must be used in addition to the real-valued data. The rational-fraction methods are tested for two systems : (a) the energy difference between the 3σ and 4σ states of HeH⁺⁺ and (b) the energy difference between the two lowest singlet states of H₃ ⁺ at collinear geometries. In both cases, the rational fractions accurately represent the actual potentials on the real axis and when analytically continued into the complex nuclear coordinate plane. In (b), the first derivatives of the rational fractions are calculated and found to be sufficiently accurate for semiclassical calculations on molecular collisions.     

MRCI potential energy curves and analytical potential energy functions for the X2∑+ and 2П states of BO molecule

t APEFs are accurate and can display the interaction between the atoms well. The present APEFs can be used to construct more complicated APEF or do some dynamic investigations.     

Exchange-Coulomb potential energy surfaces and related physical properties for Ne-N2

An exchange-Coulomb (XC) potential energy model is developed for the Ne-N₂ interaction. The construction of this new potential energy surface is based on recent results for the Heitler-London interaction energy, the long range dispersion energies, and the microwave spectra of the dimer. The adjustable parameters in the final XC1 potential energy surface have been determined by fitting the frequencies of three representative lines of the microwave spectrum for the two isotopomers ²⁰Ne-¹⁴N₂ and ²⁰Ne-¹⁵N₂ while simultaneously maintaining agreement with the experimental second virial coefficient data obtained with the initial (unadjusted XC0 potential. With no further adjustment of parameters, the final XC potential reproduces, within 0.005%, the frequencies of the 34 microwave transitions studied experimentally for four isotopomers of Ne-N₂. Excellent agreement with experiment is obtained also for the binary diffusion, the interaction viscosity, and the mixture viscosity (for all compositions) coefficients for all temperatures. Agreement with experiment for the relaxation cross-sections associated with viscomagnetic effects, and with the pressure broadening of depolarized Rayleigh light scattering, is very good given the level of computation used for the calculations and the accuracy with which some of these cross-sections currently can be determined from experimental data. Comparisons are made with predictions calculated from the three best literature potential energy surfaces or Ne-N₂. The final XC1 potential energy surface is overall the most reliable potential energy for this van der Waals complex to date. The flexibility still inherent in this potential can be exploited, if required, in future studies of the Ne-N₂ system.     

AuZn和AuAl分子基态与低激发态的势能函数与热力学性质

用密度泛函理论B3LYP方法计算研究AuZn和AuAl分子基态与低激发态的结构与势能函数,导出分子的光谱数据.结果表明,AuZn和AuAl分子基态分别为X²Σ和X¹Σ,基态与低激发态的势能函数均可用Murrell-Sorbie函数来表达.AuZn分子低激发态a⁴Σ的绝热激发能为43529kJ/mol,AuAl分子低激发态a³Σ的绝热激发能为19991kJ/mol.计算固体AuZn和AuAl的内能和熵时,近似以气体分子的电子能和振动能代替固体分子的内能,用电子熵和振动熵代替固体分子的熵.在此近似下,计算得到AuZn和AuAl基态与低激发态固态分子生成反应热力学性质与温度的关系. 关键词： AuZn和AuAl B3LYP 热力学性质 势能函数     

Analytical potential energy functions for the ground and some excited states of N2

The analytical potential energy functions have been calculated for the ground state X¹Σ⁺_g and four excited electronic states a¹Π_g, A³Σ⁺_u, B′³Σ^?_u and B³Π_g of N₂ molecule using the algebraic and energy-consistent methods (AM-ECM). Based on our previously published full AM vibrational energies and spectroscopic constants, the low-lying force constants f_n, the expansion coefficients a_n and the variational parameters λ in the AM–ECM potentials are determined for these states. The computed AM–ECM potential energy curve of each state is in excellent agreement with the experimental data and better than other analytical potentials.     

Efficient generation of flexible-monomer intermolecular potential energy surfaces

A new method of generating flexible-monomer intermolecular interaction potentials has been proposed. The method, based on symmetry-adapted perturbation theory, extends a rigid-monomer potential into a flexible-monomer one at a cost negligible compared to performing calculations on a full-dimensional grid (i.e., including internal degrees of freedom of monomers). The non-rigidity effects are accounted for by density-overlap integrals and by asymptotic expansion coefficients. Results for a model system (Ar-HF) demonstrate that the method recovers a substantial portion of these effects.     

New spectroscopic analyses and potential energy curves for the X1Σ+ and A1Σ+ states of NaH

The emission spectrum of NaH has been photographed in the ～6000–7300-Å region. Additional bands of the A¹Σ⁺ electronic transition have been analyzed and in particular the observed vibrational structure of the excited A state has been extended down to v′ = 0. New spectroscopic constants have been obtained, the v′ = 0 data leading to especially large changes in the constants of the anomalous A¹Σ⁺ state. New Rydberg-Klein-Rees (RKR) potential energy curves have been calculated up to v″ = 8 of the X¹Σ⁺ state and up to v′ = 20 in the A¹Σ⁺ state.     

The true potential energy curves for different states of SiO and SiS molecules

The true potential energy curves forX ¹ Σ ⁺, a³ π _r,A ¹ π,e ³ Σ ⁻,E ¹ Σ ⁺,c ³ π _i states of astrophysically important molecule SiO, whose spectra were observed in the sunspots, have been constructed using the method of Lakshman and Rao. Dissociation energy and ionization potential have been estimated as 65,350 cm⁻¹ and 92,854 cm⁻¹ respectively and found to be in good agreement with the values cited in literature. The true potential energy curves forX ¹ Σ ⁺,D ¹ π andE ¹ Σ ⁺ states of SiS molecule have been constructed by the same method and its dissociation energy in the ground state has been estimated using Hulburt-Hirschfelder potential function as 54,765 cm⁻¹ in good agreement with 53,250.9 cm⁻¹ given by Herzberg.     

The potential energy surfaces and the giant dipole resonances of46,48,50Ti

The low energy and giant dipole resonance properties of^46,48,50Ti have been investigated within the framework of the collective model of Gneuss and Greiner. The starting potential energy surfaces were taken from Rebel and Habs from which the low energy properties were compared with both an asymmetric rotator model and a shell model calculation. The giant dipole absorption cross sections compared favourably with the experimental data. However, the scarcity of data relating to theγ-scattering from the giant dipole resonance states to the low lying levels made any detailed comparison incomplete.     

Potential energy surfaces in algebraic molecular models using coherent states

The potential energy surfaces provided by the coherent states formalism for the case of interacting one-dimensional oscillators is investigated. The case of two interacting oscillators modelled with Morse potentials are considered in detail. First the traditional treatment is presented in order to identify the need to establish a new transformation between the parameters and the classical variables that allow the full Hamiltonian to be recovered. To this end the connection between the su(2) algebraic model and the usual treatment in configuration space was taken into account. It is shown that the coherent state approach when applied to recover the potential energy surface (PES) from a polyad preserving Hamiltonian is viable only in systems with a local mode behaviour. For molecules with a normal mode behaviour the approach is still valid, but the polyad must be broken in order to recover the PES. Our approach is evaluated through the calculation of the force constants for H₂O and CO₂, representative examples of local and normal behaviours.