卤素双原子分子部分电子态的完全振动能谱和离解能

用代数方法(AM)可以获得双原子分子包含最高振动能级在内的所有高阶振动能级的完全振动能谱; 基于Leroy和Bernstein的能级表达式, 研究了卤族元素双原子分子Cl2-A’3∏(2u)、Br2-X1∑+g和I2-0+u电子态的完全振动能谱和离解能, 得到的理论结果与实验符合得很好.     

分子转动和激光脉冲对多光子激发控制的影响(英文)

用解析代数方法研究了分子转动和激光脉冲对双原子分子多光子激发控制的影响并推导得到不同转动通道下的分子振动激发几率的解析表达式.为了考察转动能级和考虑分子转动后与激光场夹角的变化对分子多光子振动激发和振动激发控制的影响,我们计算并比较了分子纯振动和加入分子转动两种情况,并分别给出了分子与极化激光场在不同取向角下三光子选择激发的图像.研究发现分子的转动能级对多光子非共振激发有修正作用,但是分子转动会降低多光子激发的选择性,而选择合适的激光脉冲形状有利于目标多光子激发控制的实现.文中还进一步讨论了激光脉冲初相位对分子多光子激发控制的影响,发现脉冲初相位对多光子激发过程有明显的调制作用.     

氢同位素双原子分子的解析势能函数

研究从重水中分离出T2 .首先,根据光谱常数导出氢同位素双原子分子Extended Rydberg的分析函数,基于同位素效应计算OT(X 2Пi)的光谱常数,有助导出三原子分子,如DTO 的解析势能函数.将这些Extended Rydberg解析势能函数用于氘交换分离氚的热力学与分子反应动力学研究.此外,由同位素位移极值得到当振动量子数vmax≈11.5,振动能级间隔△Ev(H2)≈△Ev(T2),若v△Ev(T2)和v>vmax时,△Ev(H2)<△Ev(T2).因而,温度较低时,平衡移向T2;温度较高时,平衡移向H2 .与文献结果相似 ,而导出方法不同.     

在激波波面中氧分子的非平衡离解

对强激波作用下双原子分子振动与离解耦合的非平衡离解过程进行了理论计算.本工作的特点是将计算起点建立在分子基本参数上,采用主方程理论处理振动与离解的耦合,振动跃迁几率用SSH理论计算,在离解限附近考虑多量子数跃迁并计及原子复合的影响.对O2－Ar体系,计算给出了在正激波后O2分子振动能级分布、振动弛豫时间、离解孕育时间、离解产物浓度、离解速率系数等物理量随时间的演化.计算结果分别与Camac 和Wray的实验相符.计算显示，在激波作用的后期,有准稳态的振动能级布居分布.计算结果显示，Park模型低估了非平衡离解速率系数,Hansen模型则高估了非平衡离解速率系数.     

从分子图像到热力学框架——物理化学教学的探讨与实践

化学的核心是基于原子分子的图像认识世界、创造物质,化学教育需要培养学生掌握相应的思维方式。在物理化学类课程建设中,浙江大学化学系尝试把宏观化学的基本理论框架,即热力学理论建立在原子分子水平上。具体地是先简述量子化学对单个原子、分子能级结构的处理,然后利用统计热力学的基本原理,从这些量子化的能级导出宏观系统的三个基石性概念(能量、熵、温度)和一条基本定律(熵增加原理),从而建立分子图像的热力学。在教学实践中,强调直接从原子分子层面切入、弱化热机理论、理论与实验结果直接关联。在本文中,我们通过几个教学实例来分享我们的教学经验。     

复合物C6H5CH3…Ar分子间的外部振动频率

利用双光子共振电离光谱和飞行时间质谱技术在超声分子束中观察到C6H5CH3…Ar的振动光谱.借助同位素光谱效应、内转动能级和分子间振动能级的理论计算,合理地归属了涉及CH3转动和Ar原子振动的光谱,并由此获得复合物分子间各种模式的振动频率.     

笼状碳氢化合物五环[5.4.0.02，6.03，10.05，9]十一烷的密度泛函理论研究

运用密度泛函理论,在B3LYP/6-31G**水平上,对典型高能量密度笼状化合物五环[5.4.0.02,6.03,10.05,9]十一烷（PCU）进行了理论计算。基于上述水平全优化分子结构的键长、键角及二面角求得PCU分子的张力能;用Monte-Carlo方法得到化合物的理论密度;由简谐振动分析求得IR谱,计算结果与实验良好相符;基于振动分析,由统计热力学求得PCU的热力学性质;采用GIAO方法求得PCU的13C-NMR和1H-NMR谱的化学位移,计算结果与实验结果的线性相关性均大于0.99,计算结果可辅助解析PCU的NMR谱。     

反应碰撞的动力学李代数描述

提出一种李代数方法描述分子反应碰撞问题．给出了含有主要动力学参量的S-矩阵元、分子碰撞跃迁几率以及反应体系能量统计平均值随时间演化的解析表达式．讨论了一个简单排斥势场中的原子-双原子分子共线反应体系，以阐明这种新方法的要点。     

Hückel分子轨道计算的割键法则及其应用

对于共轭分子的H(?)ckel分子轨道和能级计算,唐敖庆等提出了图论法.在前人的工作基础上,本文提出割键法则.文中首先引入键率的概念,将轨道系数和能级的计算问题转化为键率和能级的计算问题.遵守文中建立的割键法则,割断分子结构图中若干个键,同时改造原子的库仑积分,就能将复杂的分子结构图用互相独立的子图集合来代替.每个子图的久期行列式都应等于零.据此,就能建立起以能级和键率为未知数的方程组(称为键率方程组),解之即得能级和键率.由于子图结构简单,所以应用此法可使计算工作大为简化,此法广泛地适用于各种复杂的共轭分子.文中以杂基多基分子为例进行了计算.     

OCS电子基态势能面与振动光谱的理论研究

本文采用键长-键角内标系下的自洽场-组态相互作用方法精确计算了OCS分子的振动高激发态能级,并结合实验观测到的振动能级利用非线性最小二乘法优化电子基态势能函数中的势能参数。由优化所得的势能面计算出的振动激发态能级与50个实验观测到的振动能级比较,标准偏差为0.08cm^-^1。此外,还用该势能面计算了OCS同位素分子的振动能级,计算结果与实验值也十分吻合。     

Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties

Thermodynamic properties of selected small and medium size molecules were calculated using harmonic and anharmonic vibrational frequencies. Harmonic vibrational frequencies were obtained by normal mode analysis, whereas anharmonic ones were calculated using the vibrational self-consistent field (VSCF) method. The calculated and available experimental thermodynamic data for zero point energy, enthalpy, entropy, and heat capacity are compared. It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities. Limitations of the current VSCF method for low frequency modes have been partially removed by following normal mode displacements in internal, rather than Cartesian, coordinates.     

N-丙烯酰吩噻嗪异构体的量子化学研究

用量子化学从头算方法 ,在RHF/ 6_31G 的水平上 ,对N_丙烯酰吩噻嗪分子两种异构体进行了理论计算 ,优化得到了它们的平衡几何构型 ,并计算了它们的谐振动频率 .结果表明 :N_丙烯酰吩噻嗪分子两种异构体的稳定性不同 .用PM3/CIS和AM1/CIS方法计算了它们的电子光谱 ,得到了由基态到各激发态的垂直跃迁能和相应的振子强度 .这些结果对探讨N_丙烯酰吩噻嗪引发丙烯腈聚合的机理是有益的     

Theoretical investigation of molecular properties of the first excited state of the phenoxyl radical

A theoretical study of molecular, electronic, and vibrational properties of the first excited state of the phenoxyl radical, A 2B2, is presented. The calculated molecular geometries, vertical and adiabatic excitation energies, and harmonic vibrational frequencies are compared with analogous results obtained for the ground state. The calculated excitation energies correspond well to experimental data. The harmonic vibrational frequencies of the A 2B2 and the ground state are similar except for modes involving the vibrations of the CO bond.     

Parameterization and evaluation of a flexible water model

The thermodynamic, dielectric, and dynamic properties of a newly parameterized flexible water model are studied using molecular dynamics simulations. The potential function developed is based on the popular simple point charge (SPC) rigid model with the addition of appropriate harmonic and anharmonic energy terms for stretching and bending. Care was taken to account for the self-polarization and gas-phase monomer energy corrections during the parameterization, which have typically been ignored in past studies. The results indicate that an increased Lennard-Jones repulsive coefficient and slightly scaled partial charges are required when adding flexibility to the rigid model potential to reliably reproduce the experimental density, energy, and O ? O radial distribution function of water at 298 K and 1 atm. Analysis of the power spectrum derived from the H-velocity autocorrelation function allowed the water potential to be evaluated further and refined by adjusting the valence forces to fit the vibrational frequencies of the gas and liquid. Once a consistent set of parameters was determined, the static dielectric properties of the water model were calculated at two temperatures using the reaction field method to treat long-range forces and correlations. The dielectric constant of 75 ± 7 calculated at 300 K is in good agreement with the experimental value of 78.5. The Kirkwood g factor was also examined for temperature dependence and showed the correct increasing behavior with decreasing T. As a final check of the water potential, the free energies of solvation of a flexible water molecule and neon were predicted using thermodynamic perturbation methods. The calculated solvation energies of ?7.0 ± 0.8 for water and 2.7 ± 0.7 for neon are both consistent with the experimental values of ?6.3 and 2.7 kcal/mol. Comparisons are made throughout the study with the results of previous rigid and flexible model simulations. © 1995 by John Wiley & Sons, Inc.     

Origin of stability of the high-temperature, low-pressure Rh2O3 III form of rhodium sesquioxide

We present a first principles study of the equilibrium structures and relative thermodynamic stability of the three observed polymorphs of rhodium(III) sesquioxide. The thermodynamic Gibbs free energies for each phase are calculated as a function of P and T based on the electronic total energy, as well as vibrational energy and vibrational entropy contributions in the local harmonic (LH) approximation. The results confirm that Rh₂O₃ I is a low-temperature, low-pressure form and Rh₂O₃ II is a high-pressure form. A breakdown in the LH approximation at high T is then discussed and to address this breakdown an empirically corrected local harmonic (ECLH) approximation is introduced. ECLH demonstrates that the high-temperature, low-pressure form Rh₂O₃ III is entropically stabilized and produces a partitioning of phase space that is consistent with published experimental investigations.     

Converged vibrational energy levels and quantum mechanical vibrational partition function of ethane

The vibrational partition function of ethane is calculated in the temperature range of 200-600 K using well-converged energy levels that were calculated by vibrational configuration interaction, and the results are compared to the harmonic oscillator partition function. This provides the first test of the harmonic oscillator approximation for a molecule with more than five atoms. The absolute free energies computed by the harmonic oscillator approximation are in error by 0.59-0.62 kcal/mol over the 200-600 K temperature range.     

Conformational and thermodynamic properties of gaseous levulinic acid

Molecular modeling is used to determine low-energy conformational structures and thermodynamic properties of levulinic acid in the gas phase. Structure and IR vibrational frequencies are obtained using density functional and M?ller-Plesset perturbation theories. Electronic energies are computed using G3//B3LYP and CBS-QB3 model chemistries. Computed anharmonic frequencies are consistent with reported experimental data. Population analysis shows a boat- and a chainlike structure to be most abundant at 298 K, with increasing proportions of two other conformers at higher temperatures. Population mean distribution values for thermodynamic quantities are derived. At 298 K and 1 atm, the enthalpy of formation, entropy, and heat capacity are -613.1 ± 1.0 kJ·mol(-1), 407.4 J·mol(-1)·K(-1), and 132.3 J·mol(-1)·K(-1), respectively.     

Electron and Geometry Structure of Hydrogen-Bonded Complexes of Guanine with One Molecule Methanol. A DFT Level Study

Summary. The geometries, harmonic vibrational frequencies, and energies of eight hydrogen-bonded complexes of guanine with one molecule methanol are computed using the DFT (B3LYP) method together with the 6-31+G* basis functions. In the investigation two stable tautomers of guanine (oxo-amino N9H and oxo-amino N7H) were chosen. They were included in a variety of H-bonded complexes with one molecule methanol. In order to investigate the nature of the intermolecular bonds, the bonding energies and thermodynamic properties of the complexes were calculated.     

Vibrational investigation on FT-IR and FT-Raman spectra, IR intensity, Raman activity, peak resemblance, ideal estimation, standard deviation of computed frequencies analyses and electronic structure on 3-methyl-1,2-butadiene using HF and DFT (LSDA/B3LYP/B3PW91) calculations

FT-IR and FT-Raman (4000–100 cm⁻¹) spectral measurements of 3-methyl-1,2-butadiene (3M12B) have been attempted in the present work. Ab-initio HF and DFT (LSDA/B3LYP/B3PW91) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, IR intensities and Raman activities. Complete vibrational assignments on the observed spectra are made with vibrational frequencies obtained by HF and DFT (LSDA/B3LYP/B3PW91) at 6-31G(d,p) and 6-311G(d,p) basis sets. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The potential energy distribution (PED) corresponding to each of the observed frequencies are calculated which confirms the reliability and precision of the assignment and analysis of the vibrational fundamentals modes. The oscillation of vibrational frequencies of butadiene due to the couple of methyl group is also discussed. A study on the electronic properties such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties of the title compound at different temperatures reveal the correlations between standard heat capacities (C) standard entropies (S), and standard enthalpy changes (H).     

Electron and Geometry Structure of Hydrogen-Bonded Complexes of Guanine with One Molecule Methanol. A DFT Level Study

The geometries, harmonic vibrational frequencies, and energies of eight hydrogen-bonded complexes of guanine with one molecule methanol are computed using the DFT (B3LYP) method together with the 6-31+G* basis functions. In the investigation two stable tautomers of guanine (oxo-amino N9H and oxo-amino N7H) were chosen. They were included in a variety of H-bonded complexes with one molecule methanol. In order to investigate the nature of the intermolecular bonds, the bonding energies and thermodynamic properties of the complexes were calculated.