哌嗪二酮的气相Hel光电子能谱及其量化计算

给出了哌嗪二酮的气相HeI紫外光电子能谱(UPS), 并进行了化合物分子的HAM/3, MNDO, MINDO/3, INDO, CNDO/2和EHMO等量子化学计算研究. UPS谱低电离能(<11.00 eV)区的四重峰被指认为分子体系中氧-氧, 氮-氮原子孤对轨道间的通过键相互作用导致的分裂峰. 表明HAM/3和MNDO计算法是预指该化合物实验电离能正确次序、轨道对称性类型以及通过键相互作用导致分裂大小的较好方法.     

用HAM/3法研究胞嘧啶及其甲基衍生物的光电子能谱与紫外光谱

本文用半经验SCF-MO-HAM/3方法计算了胞嘧啶和它的某些甲基衍生物的电离能、激发能和振子强度.指认了这些分子的紫外光电子能谱和紫外电子光谱.讨论了在紫外光电子能谱指认上与CNDO/S的不同之处.分析了胞嘧啶在磷酸三甲酯中可能存在的主要异构体形式.     

原子簇与有关分子的结构规则——Ⅲ.硼烷、碳硼烷、立方烷和棱柱烷的电子结构

本文用Asbrink,Fridh和Lindholm提出的自洽场近似分子轨道法HAM/3程序计算了若干典型的硼烷、碳硼烷、立方烷和棱柱烷的电子结构,以验证本文作者之一提出的结构规则:包括原子簇在内的无机和有机分子可以认为由若干分子片的组成,它们的结构类型可由四个数(nxcπ)来规定。     

咔唑及其N-取代衍生物的气相He I紫外光电子能谱与量子化学研 究

首次系列报道了9-H咔唑及其系列N-取代衍生物的气相HeI紫外光电子能谱,借助于Gauss-94采用RHF/3-21G基组对它们的几何构型进行优化,并用RHF/6-31G基组计算分子轨道及能级,计算的分子轨道特征和能量很好地反映了各谱带的特点和分子间电离能的变化规律。依计算结果,以及同系列分子间谱带及相应电离能的相互比较,对每个分子的UPS谱带给予指认,讨论了N-烷基化对π分子轨道的选择性去稳定化作用,并讨论了分子之间电离能的变化规律,得到一系列有益的结论。     

咔唑及其N-取代衍生物的气相He I紫外光电子能谱与量子化学研 究

首次系列报道了9-H咔唑及其系列N-取代衍生物的气相HeI紫外光电子能谱,借助于Gauss-94采用RHF/3-21G基组对它们的几何构型进行优化,并用RHF/6-31G基组计算分子轨道及能级,计算的分子轨道特征和能量很好地反映了各谱带的特点和分子间电离能的变化规律。依计算结果,以及同系列分子间谱带及相应电离能的相互比较,对每个分子的UPS谱带给予指认,讨论了N-烷基化对π分子轨道的选择性去稳定化作用,并讨论了分子之间电离能的变化规律,得到一系列有益的结论。     

咔唑及其N-取代衍生物的气相HeⅠ紫外光电子能谱与量子化学研究

首次系列报道了9-H咔唑及其系列N-取代衍生物的气相HeI紫外光电子能谱,借助于Gauss-94采用RHF/3-21G基组对它们的几何构型进行优化,并用RHF/6-31G基组计算分子轨道及能级,计算的分子轨道特征和能量很好地反映了各谱带的特点和分子间电离能的变化规律.依计算结果,以及同系列分子间谱带及相应电离能的相互比较,对每个分子的UPS谱带给予指认,讨论了N-烷基化对π分子轨道的选择性去稳定化作用,并讨论了分子之间电离能的变化规律,得到一系列有益的结论.     

气态肼的三种电子能谱和量子化学研究

本文应用X射线光电子能谱技术测得了气态肼的内层电子能谱、Auger电子能谱和价带电子能谱,对其电子结构进行了系统研究。又采用了不同能量的X射线为激发源,对比了Mg Ka 和 Zr M:价带能谱,定性地获得了肼的分子轨道的组成。本文对肼电子能谱进行了量子化学研究,用从头计算法给出了分子轨道波函数的成分,并指认了能谱,实验结果和计算值之间的一致性很好。     

推/拉电子取代基对PCBM结构及光谱性质影响的理论研究

应用密度泛函理论(DFT)方法计算[6,6]-苯基-C₆₁-丁酸甲酯(PCBM)及其苯环对位取代得到的4种衍生物的几何和电子结构. 采用第一激发能校正了分子的最低未占据分子轨道(LUMO)能级, 探讨了推/拉电子基团对分子前线轨道的影响. 在全优化几何构型的基础上, 采用含时密度泛函理论(TD-DFT)方法研究了电子吸收光谱特征和电荷转移态性质, 并讨论了推/拉电子基团对体系电子吸收光谱性质的影响. 通过对重组能和电子亲和势的计算, 预测了PCBM与4种衍生物的电子能力及电子迁移率大小的关系. 结果表明, 在PCBM中, 在苯环的对位引入推电子基团可以提高分子的前线轨道能级, 改变前线轨道电子云分布, 明显增强可见光范围内的吸收强度, 增加可见光范围内的电荷转移吸收, 且激发态的电荷转移随着引入基团推电子能力的增加而增强. 化合物5的激发态分子内电荷转移性质最强, 且具有较独特的光伏性质. 而在同样位置引入拉电子基团, 则降低了分子前线轨道能级对电子吸收光谱的影响.     

含苯并五元环方酸衍生物的二阶非线性光学性质的理论研究

利用从头算HF/6-31G*方法对用苯并五元环取代的方酸衍生物体系SQ1～SQ15进行几何构型优化和电子结构计算. 以优化后的构型为基础, 应用ZINDO方法计算电子光谱. 同时应用从头算CPHF/6-31G*方法和半经验FF/AM1, FF/PM3, FF/MNDO等有限场方法计算了分子的二阶非线性光学系数β_μ. 研究几何结构、电子结构和前线分子轨道能与β_μ之间的关系, 为设计性能优良的有机非线性光学材料提供理论指导, 并对这四种计算方法的结果进行了比较.     

Re_2(edt)_4的电子结构和电子吸收光谱的从头算研究

用密度泛函理论中的B3LYP/CEP-4G方法对Re2（edt）4进行了结构优化和自然键轨道计算,并用单电子激发组态相互作用方法（CIS）计算了Re2（edt）4的分子轨道和激发态。结果表明Re-Re之间不存在明显的三重键,进而很好地解释了Re2（edt）4分子的电子吸收光谱。     

Theoretical study of valance photoelectron spectra of hypoxanthine, xanthine, and caffeine using direct symmetry-adapted cluster/configuration interaction methodology

UV photoelectron spectra of hypoxanthine, xanthine, and caffeine, up to 20 eV, were calculated and compared with the experimental spectra reported in literature. The calculations were performed using a novel version of the quantum mechanical symmetry-adapted cluster/configuration interaction (SAC-CI) method termed, direct SAC-CI. The Duning/Huzinaga valance double-zeta D95+(d,p) Gaussian basis set was also employed with this method. The ionization energies and intensities were calculated, and the corresponding spectral bands were assigned. Natural bonding orbital (NBO) calculations were employed for better spectral band assignment. The calculated ionization energies and intensities reasonably produced the experimental photoelectron spectra.     

Electronic structure of TCNQ,studied with HAM/3

The electronic structure of tetracyanoquinodimethane (TCNQ) is calculated using the new semiempirical method HAM /3. The calculated photoelectron spectrum is in reasonable agreement with the measured spectrum. The excitation energies are obtained directly in HAM as the differences of the energies of the unoccupied and the occupied orbitals. The calculated UV spectrum is in good agreement with the measurements. The weak band at 5.3 eV, which earlier had been assumed to correspond to a forbidden transition, is allowed according to HAM . The electron affinity is also in reasonable agreement with the measured value. An explanation has been given for the experimental observation of several resonance states (negative electron affinities). p-Quinodimethane has also been studied.     

A HAM/3 study of substituted benzenes

The semiempirical HAM /3 method is used to study ionization potentials, electron affinities, heats of formation, stabilization energies, dipole moments, and charge of mono- and disubstituted benzenes. Ionization potentials and electron affinities are calculated with good accuracy. The ground state properties are generally not well calculated by HAM /3. Errors in heats of formation and dipole moments are up to 50 kcal/mol and 2.4 D .     

Ab initio Study on Ionization Energies of 1-Methyl-hypoxanthine

Six low-lying tautomers of 1-methyl-hypoxanthine have been studied at the B3LYP/aug-cc-pVDZ level. Two tautomers N7H and N9H with the comparable energies are far more stable than the others. The vertical ionization energies of the tautomers calculated with ab initio electron propagator theory in the P3/aug-cc-pVDZ approximation are in agreement with the experimental data from photoelectron spectroscopy. According to the calculated relative energies and the comparison between the simulated and the experimental photoelectron spectra, it demonstrates that there are at least two tautomers of 1-methyl-hypoxanthine in the gas-phase experiments.     

NMR, UV, FT-IR, FT-Raman spectra and molecular structure (monomeric and dimeric structures) investigation of nicotinic acid N-oxide: A combined experimental and theoretical study

In this work, the experimental and theoretical UV, NMR, and vibrational features of nicotinic acid N-oxide (abbreviated as NANO, C(6)H(5)NO(3)) were studied. The ultraviolet (UV) absorption spectrum of studied compound that dissolved in water was examined in the range of 200-800nm. FT-IR and FT-Raman spectra in solid state were observed in the region 4000-400cm(-1) and 3500-50cm(-1), respectively. The (1)H and (13)C NMR spectra in DMSO were recorded. The geometrical parameters, energies and the spectroscopic properties of NANO were obtained for all four conformers from density functional theory (DFT) B3LYP/6-311++G(d,p) basis set calculations. There are four conformers, C(n), n=1-4 for this molecule. The computational results identified the most stable conformer of title molecule as the C1 form. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. (13)C and (1)H nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, absorption wavelengths, HOMO and LUMO energies, were performed by CIS approach. Finally the calculation results were applied to simulate infrared, Raman, and UV spectra of the title compound which show good agreement with observed spectra.     

苏氨酸对甲苯磺酸盐及其酯化物的微波合成、表征及量化计算

以苏氨酸(Thr)和对甲苯磺酸(p-TsOH)为原料, 用一步法在微波反应仪中合成了离子液体苏氨酸对甲苯磺酸盐(Thr-TsOH), 并采用对甲苯磺酸法一步制得其甲酯和乙酯化合物ThrC1-TsOH和ThrC2-TsOH. 对合成的离子液体的理化性质进行了表征, 它们均具有较低的熔点(低于100 ℃), 但热稳定性相对较差. 结合量化计算理论方法初步探索了氨基酸酯化对熔点的影响. 采用DFT的B3LYP/6-311++G**方法对苏氨酸对甲苯磺酸及其甲酯、乙酯化合物3种分子进行构型优化及振动频率分析, 通过对分子中阴、阳离子间结合能的研究发现, 酯化不仅能减弱分子间氢键相互作用, 还能明显减弱分子内离子间相互作用, 从而降低体系的熔点.     

Lutidyl Radical Photoelectron Spectra Reveal Additive Substituent Effects on Benzyl Derivatives’ Ionization Energy

Understanding how isomerism influences photoelectron spectra helps in the assignment and analysis of reactive mixtures, especially for heterocycles with numerous isomers. Threshold photoelectron spectra of lutidyl radical isomers, i. e., benzyl derivatives with a nitrogen heteroatom and a methyl substituent, are recorded using vacuum ultraviolet synchrotron radiation. The radicals are produced by flash pyrolysis from aminomethyl methylpyridine precursors. Experimental ionization energies are determined to be 7.54, 7.50, and 7.45 eV for 2,4-, 2,6- and 3,5-lutidyl, respectively, in excellent agreement with composite method calculations. Franck–Condon simulations aid the TPES assignment but are also shown to exhibit artifacts if large-amplitude motions, notably the methyl internal rotation are assumed to be active in the double harmonic approximation. Based on calculated adiabatic ionization energies (AIE) of benzyl, picolyl, and xylyl radicals, the N and CH₃ substituent effects are found to be additive, position-dependent and decrease in the para>ortho≳meta order in magnitude with the nitrogen heteroatom increasing and the methyl substituent decreasing the AIE. These effects are discussed in light of the charge distribution upon ionization. The additivity of the substituent effects also helps predict the influence of substituents on the binding energy of the unpaired electron in analogous radicals.     

Assignment of photoelectron spectra by the help of density functional calculations

First adiabatic and vertical ionization energies were calculated by the density functional method using Becke's correlated functional for water, ammonia, the silyl radical, five-membered heterocycles, and naphtalene. The structure of the ionic ground state and that of the neutral was optimized separately. The calculated ionization energies and harmonic frequencies are in acceptable agreement with the observed values. The calculated geometrical changes are in agreement with the information deduced from the photoelectron spectra. © 1997 John Wiley & Sons, Inc.     

Threshold-photoelectron spectroscopic study of methyl-substituted hydrazine compounds

The valence shell electronic structures of methylhydrazine (CH(3)NHNH(2)), 1,1-dimethylhydrazine ((CH(3))(2)NNH(2)) and tetramethylhydrazine ((CH(3))(4)N(2)) have been studied by recording threshold and conventional (kinetic energy resolved) photoelectron spectra. Ab initio calculations have been performed on ammonia and the three methyl substituted hydrazines, with the structures being optimized at the B3-LYP/6-31+G(d) level of theory. The ionization energies of the valence molecular orbitals were calculated using the Green's function method, allowing the photoelectron bands to be assigned to specific molecular orbitals. The ground-state adiabatic and vertical ionization energies, as determined from the threshold photoelectron spectra, were IE(a) = 8.02 +/- 0.16 eV and IE(v) = 9.36 +/- 0.02 eV for methylhydrazine, IE(a) = 7.78 +/- 0.16 eV and IE(v) = 8.86 +/- 0.01 eV for 1,1-dimethylhydrazine and IE(a) = 7.26 +/- 0.16 eV and IE(v) = 8.38 +/- 0.01 eV for tetramethylhydrazine. Due to the large geometry change that occurs upon ionization, these IE(a) values are all higher than the true thresholds. New features have been observed in the inner valence region and these have been compared with similar structure in the spectrum of hydrazine. The effect of resonant autoionization on the threshold photoelectron yield is discussed. New heats of formation (Delta(f)H) are proposed for the three hydrazines on the basis of G3 calculations: 107, 94, and 95 kJ/mol for methylhydrazine, 1,1-dimethyhydrazine and tetramethylhydrazine, respectively. The previously reported Delta(f)H for tetramethylhydrazine is shown to be erroneous.