CFCl3的理论和紫外光电子能谱研究

采用紫外光电子能谱(PES)和量子化学方法,研究了以CFCl3化合物为代表的系列化合物(CFCl3、CF2Cl2、CF3Cl、CCl4)不同离子态的电子结构和性质。结果表明,四种化合物CF3Cl、CF2Cl2、CFCl3、CCl4的第一电离能依次下降。结合从头算自洽场分子轨道(abinitioSCFMO)和外壳层格林函数法(OVGF)计算对化合物的PES进行了分析和指认,表明化合物的外层轨道中Cl的孤对电子成分对电离能存在明显的影响;外层格林函数法计算得到电离能与实验吻合很好;同时发现在外壳层格林函数法计算结果中由于考虑相关能,得到的分子轨道存在能级顺序的交错。     

缩胺基硫脲衍生物电子结构的HeI紫外光电子能谱研究

报道了一组具有生物活性的缩胺基硫脲衍生物电子结构的HeI紫外光电子能谱(PES)研究。PES谱的指认借助于对有类似原子基团的小分子的PES结果以及对每个研究分子的MNDO量子化学计算,同时由PES实验最低电离能(IP_s/eV)预指了该类衍生物间的相对生物活性大小,而研究分子最高占有轨道(HOMO)的π键属性促进了人们对这类衍生物生物活性的了解。     

缩胺基脲衍生物HeI PES和电子结构的研究

利用HeI紫外光电子能谱(PES)首次得到一组缩胺基脲衍生物的PES谱图。并利用RHF(6-31G^*^*)计算了它们的电子结构,解析了实验谱,分析和说明与实验电离能所对应的分子轨道的特征。论证了计算结果与实验值间很好的相符关系。并通过实验和计算结果,讨论了这类化合物取代基的影响和为何缺乏生物活性。     

PAN和PPN的HeI光电子能谱（PES）

给出了两个重要的大气污染化合物PAN和PPN的紫外光电子能谱（PES）。为了 指认PES谱,对两个分子实施了HF和OVGF方法的理论计算,并给出了它们各自的优 化几何构型、PES谱低电离能区的两个分离（PAN）为11.42 eV和12.07 eV;PPN为 11.08 eV和11.79 eV）被归于分子中主要体现“NO_2”基团贡献的最高占有分子轨 道（HOMO）和次最高占有分子轨道（SHOMO）电子电离作用结果。而PPN的第一电离 能11.08 eV低于PAN的11.42 eV,是由于PPN分子中增加的“CH_2”基团电子的给予 作用,这为PPN应具有较大的生物毒性提供合理的解释。     

邻硝基乙酰苯胺衍生物电子结构的UPS研究

本文报道邻硝基乙酰苯胺衍生物的HeI紫外光电子能谱(PES), 同时也给出了邻硝基苯胺衍生物的PES谱。PES谱的指认由相应分子的MNDO计算所支持, 并指出带有不同取代基基团的邻硝基乙酰苯胺合成耐高温喹啉高聚物的难易依赖于PES所测化合物分子的最低电离能(IP)。     

两种影响生态环境的亚硝基取代烷烃的电子结构

采用紫外光电子能谱实验(PES)和量子化学方法对两种影响生态环境的亚硝基取代烷烃RONO[R=(CH3)2CH,(CH3)3CO]的电子结构进行了分析和讨论。实验得到两种化合物的第一电离能分别为10.37eV和10.12eV,结合从头算自洽场分子轨道(abinitioSCFMO)计算和外壳层格林函数法(OVGF)计算对PES进行了分析和指认。研究表明化合物中取代基效应对电离能存在明显的影响;外层格林函数法计算得到电离能与实验吻合很好;同时发现在外层格林函数计算结果中由于考虑相关能,得到的分子轨道存在能级顺序的交错。实验和理论计算结果进一步证实亚硝基取代烷烃是产生烷基氧自由基(RO^.)的很好的源物种,这为深入研究由它们产生的对环境破坏有着重要影响的相应自由基奠定了基础。     

苯氰基衍生物气相HeI紫外光电子能谱研究

气相Hel（21．22eV）紫外光电子能谱（UPS）能从孤立分子的分子轨道特性上，给出研究分子的轨道能量、电子结构以及成键特性的大量信息．UPS谱的特性揭示了被电离分子轨道的成键性质，而量子化学计算能正确地指认UPS谱带的归属，从而化合物的UPS研究从分子轨道的属性上提供了研究体系的实验和理论基础．苯基腈（C6H5CN）的UPS已有过研究［1-3］，但作为系列分子的间-二氰基苯（1）、对-二氰基苯（2）、1；2，4，5-四氰基苯（3）的HeI光电子能谱未见报道．这一系列分子的特点是-CN取代的数目和位置不同，通过这些分子UPS的研究找…     

杜鹃花科植物有毒成分的电子结构及构效关系

本文应用INDO方法, 对由杜鹃花科植物中提取分离的九个化合物进行了量子化学计算, 得到了分子轨道波函数等多种电子结构信息, 并计算了这些化合物活性部位的分子静电势, 得到了静电势图。用分子图形技术与药理性质相同的其它生物碱类毒素进行了空间结构比较。研究了它们的电子结构特征和活性部位, 讨论了作用机理及电子结构与毒性之间的关系。     

噻吩多烯基噻吩酮系列化合物的气相紫外光电子能谱研究

本文提供了噻吩多烯基噻吩酮系列化合物的气相HeI光电子能谱(UPS), 并进行了每个研究分子的MNDO量子化学计算。 表明乙烯基基团的数目与其分子的HOMO实验电离能(L~p)呈线性递降关系。MNDO计算结果不但很好地指认了每个研究分子UPS谱的归属, 而且从分子轨道特性上提供了该类化合物分子为三岔共轭体系的理论基础。     

分子晶体电子能带的结构特征

本文研究了分子晶体电子能带的结构,指出:分子晶体电子能带的位置由分子的分子轨道能级决定,而能带宽度由各个分子中分子轨道间的相互作用决定。由此出发,提出了计算分子晶体的电子能带的简便方法。     

VUV and photoelectronic spectra of methylstannane. Theoretical and experimental approach

The vacuum ultraviolet (VUV) and photoelectron spectra of SnH₃CH₃ were recorded between 6.20 and 11.28 eV and between 8 and 17 eV, respectively. Spectra were interpreted using ab initio CI calculations. The photoelectron spectrum confirmed the low SnC bond energy. The first two ionization potentials (IP) observed were attributed to the ionization of the a₁ (10.65 eV) and e orbitals (11.15 and 11.60 eV, split by the Jahn-Teller effect), thereby showing an inversion of IPs compared with ethane. Similarly, the first two bands of the VUV spectrum (at 7.04 and 7.72–8.16 eV) were attributed to a₁ and e transitions towards the Rydberg s orbital. A splitting of the same order of magnitude as that of the photoelectron spectrum could be noted in the E state. Observed transitions between 8.65 and 10 eV showed a strong interaction between the Rydberg p MO and the σ^*_SnC antibonding orbital. Primarilyvalence transitions were encountered beyond 10 eV.     

The electronic states of 1,2,4-triazoles: a study of 1H- and 1-methyl-1,2,4-triazole by vacuum ultraviolet photoabsorption and ultraviolet photoelectron spectroscopy and a comparison with ab initio configuration interaction computations

The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1,2,4-triazoles, the first ionization energy bands show complex vibrational structure on the low-energy edges of otherwise unstructured bands. Detailed analysis of these bands confirms the presence of three ionized states. The 6-7 eV VUV spectral region shows an unusual absorption plateau, which is interpreted in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The "fingerprint" of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C-H is substantially out of plane.     

The Jahn-Teller effect in CH(3)CN(+) (X(2)E) and CD(3)CN(+) (X(2)E) studied by zero kinetic energy photoelectron spectroscopy

The Jahn-Teller effect in CH(3)CN(+) (X(2)E) and CD(3)CN(+) (X(2)E) has been found experimentally by zero kinetic energy (ZEKE) photoelectron spectroscopy using coherent extreme ultraviolet (XUV) radiation. The vibronic bands of CH(3)CN(+) (X(2)E) and CD(3)CN(+) (X(2)E) at about 4500 cm(-1) above the ground states have been recorded. The spectra consist mainly of the Jahn-Teller active C-C[triple bond]N bending (v(8)), the CN stretching (v(2)), the CH(3) (CD(3)) deforming (v(6)), and the C-C stretching (v(4)) vibronic excitations. The Jahn-Teller active vibronic bands (v(8)) have been assigned with a harmonic model including linear and quadratic Jahn-Teller coupling terms, taking into account only the single mode vibronic excitation. The ionization potentials of CH(3)CN and CD(3)CN have also been determined, and their values are 12.2040(+/-0.001) and 12.2286(+/-0.001) eV, respectively.     

Importance of vibronic effects on the circular dichroism spectrum of dimethyloxirane

We present a theoretical study on the vibrational structure of a circular dichroism (CD) spectrum using time-dependent density-functional theory in combination with a Franck-Condon-type approach. This method is applied to analyze the complex CD spectrum of dimethyloxirane, which involves delicate cancellations of positive and negative CD bands. Our approach reveals that these cancellations are strongly affected by the shapes of the CD bands, and that it is vital for an accurate simulation of the spectrum to take the different envelopes of these bands into account. One crucial point in some former theoretical studies on this compound, which were restricted to vertical excitations, was the appearance of a strong negative CD band in the energy range of 7.0-7.5 eV, which is not present in the experimental spectrum. We can explain the disappearance of this 2B band by a strong vibrational progression along normal modes with C-O stretching character, so that the band extends over an energy range of almost 1.1 eV. Thus, it overlaps with many other (mostly positive) CD bands, leading to a cancellation of its intensity. The dominant vibrational features in the experimental spectrum can be assigned to the 1B, 3B, and 5B bands, which show several clear vibrational peaks and a total bandwidth of only 0.3-0.5 eV. In order to obtain close agreement between the simulated and the experimental spectrum we have to apply small shifts to the vertical excitation energies that enter the calculation. These shifts account both for possible errors in the time-dependent density-functional theory calculations and for the neglect of differential zero-point energy between ground and excited states in our gradient-based vertical Franck-Condon approach.     

Experimental investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part II. Vibrational analysis of the A 2E"3-X 2E"2 electronic transition

Laser-induced fluorescence (LIF) and laser-excited dispersed fluorescence (LEDF) spectra of the cycloheptatrienyl (tropyl) radical C7H7 have been observed under supersonic jet-cooling conditions. Assignment of the LIF excitation spectrum yields detailed information about the A-state vibronic structure. The LEDF emission was collected by pumping different vibronic bands of the A 2E"3<--X 2E"2 electronic spectrum. Analysis of the LEDF spectra yields valuable information about the vibronic levels of the X 2E"2 state. The X- and A-state vibronic structures characterize the Jahn-Teller distortion of the respective potential energy surfaces. A thorough analysis reveals observable Jahn-Teller activity in three of the four e'3 modes for the X 2E"2 state and two of the three e'1 modes for the A 2E"3 state and provides values for their deperturbed vibrational frequencies as well as linear Jahn-Teller coupling constants. The molecular parameters characterizing the Jahn-Teller interaction in the X and A states of C7H7 are compared to theoretical results and to those previously obtained for C5H5 and C6H6+.     

Ab initio and electron propagator theory study of boron hydrides

Boron hydrides (BH3, B2H6, B3H7, B4H10, B5H9, and B5H11) and their cations are studied by the coupled cluster CCSD(T) theory, the second-order Mller-Plesset (MP2) perturbation method, and the electron propagator theory in the partial third-order quasi-particle approximation, using the 6-311G(d,p) basis set. The vertical ionization potential energies are calculated, indicating an excellent agreement with the experimental data from photoelectron spectroscopy. Assignments to the experimental spectra are made on the basis of the present computational analyses. A significant Jahn-Teller effect on BH3+ leads to two states, 2A1 and 2B2, with the split energy of 0.14 eV. The triple and double B-H-B bridges are formed in B2H6+ and b-B3H7+, respectively. A new B-H-B bridge is formed while two B-B bonds are broken in B5H11+. The Jahn-Teller effect lowers the symmetry of B5H9 (C4v) to B5H9+ (C2) but slightly influences the structure of ara-B4H10 (C2v). The calculated properties of geometries, vibrational frequencies, and energies are compared with the experimental data available in the literatures.     

Collision-energy-resolved Penning ionization electron spectroscopy of bromomethanes (CH3Br, CH2Br2, and CHBr3) by collision with He*(2(3)S) metastable atoms

Ionization of bromomethanes (CH3Br, CH2Br2, and CHBr3) upon collision with metastable He*(2(3)S) atoms has been studied by means of collision-energy-resolved Penning ionization electron spectroscopy. Lone-pair (nBr) orbitals of Br4p characters have larger ionization cross sections than sigma(C-Br) orbitals. The collision-energy dependence of the partial ionization cross sections shows that the interaction potential between the molecule and the He*(2(3)S) atom is highly anisotropic around CH3Br or CH2Br2, while isotropic attractive interactions are found for CHBr3. Bands observed at electron energies of approximately 2 eV in the He*(2(3)S) Penning ionization electron spectra (PIES) of CH2Br2 and CHBr3 have no counterpart in ultraviolet (He I) photoionization spectra and theoretical (third-order algebraic diagrammatic construction) one-electron and shake-up ionization spectra. Energy analysis of the processes involved demonstrates that these bands and further bands overlapping with sigma(C-Br) or piCH2 levels are related to autoionization of dissociating (He+ - Br-) pairs. Similarly, a band at an electron energy of approximately 1 eV in the He*(2(3)S) PIES spectra of CH3Br has been ascribed to autoionizing Br** atoms released by dissociation of (unidentified) excited states of the target molecule. A further autoionization (S) band can be discerned at approximately 1 eV below the lone-pair nBr bands in the He*(2(3)S) PIES spectrum of CHBr3. This band has been ascribed to the decay of autoionizing Rydberg states of the target molecule (M**) into vibrationally excited states of the molecular ion. It was found that for this transition, the interaction potential that prevails in the entrance channel is merely attractive.     

Vibronic structure of the permanganate absorption spectrum from time-dependent density functional calculations

The UV absorption spectrum of the permanganate anion is a prototype transition-metal complex spectrum. Despite this being a simple d0 Td system, for which a beautiful spectrum with detailed vibrational structure has been available since 1967, the assignment of the second and third bands is still very controversial. The issue can be resolved only by an elucidation of the intricate vibronic structure of the spectrum. We investigate the vibronic coupling by means of linear-response time-dependent density functional calculations. By means of a diabatizing scheme that employs the transition densities obtained in the TDDFT calculations in many geometries around Re, we construct a Taylor series expansion in the normal coordinates of a diabatic potential energy matrix, coupling 24 excited states. The simulated vibronic structure is in good agreement with the experimental absorption spectrum after the adjustment of some of the calculated vertical excitation energies. The peculiar blurred vibronic structure of the second band, which is a very distinctive feature of the experimental spectrum, is fully reproduced in the calculations. It is caused by the double-well shape of the adiabatic energy surface along the Jahn-Teller active e mode of the allowed 1E state arising from the second 1T2 state, which exhibits a Jahn-Teller splitting into 1B2 and 1E states. We trace the double-well shape to an avoided crossing between two diabatic states with different orbital-excitation character. The crossing can be explained at the molecular orbital level from the Jahn-Teller splitting of the set of 7t2{3d(xy), 3d(xz), 3d(yz)} orbitals (the LUMO + 1), to which the excitations characterizing the diabatic states take place. In contrast to its character in the two well regions, at Re the 2(1)T2 state is not predominantly an excitation to the LUMO + 1, but has more HOMO - 1 --> LUMO (2e = {3d(x2-y2), 3d(z2)}) character. The changing character of the 2(1)T2 - 1E state along the e mode implies that the assignment of the experimental bands to single orbital transitions is too simplistic intrinsically. This spectrum, and notably the blurring of the vibronic structure in the second band, can be understood only from the extensive configurational mixing and vibronic coupling between the excited states. This solves the long-standing assignment problem of these bands.     

Electronic structure and molecular properties of the heptacyanorhenate [Re(CN)7]3- and [Re(CN)7]4- complexes

We report scalar relativistic and Dirac scattered wave (DSW) calculations on the heptacyanorhenate [Re(CN)7](3-) and Re(CN)7(4-) complexes. Both the ground and lowest excited states of each complex split by spin-orbit interaction by about 0.3 eV. The calculated molecular electronegativities chi indicate that the open-shell complex is less reactive than the closed-shell complex, in agreement with experimental observations. The calculations indicate that the ground state spin density is highly anisotropic and that spin-orbit effects are responsible for the magnetic anisotropy of the molecular g tensor of the Re(CN)7(3-) complex. The calculated optical electronic transitions for both complexes with a polarizable continuum model using a time-dependent density functional (TDDFT)/B3LYP formalism are in reasonable agreement with those observed in the absorption spectrum.     

Analysis of the intermolecular interactions between CH3OCH3, CF3OCH3, CF3OCF3, and CH2F2, CHF3

The intermolecular interaction energy curves of CH(3)OCH(3)-CH(2)F(2), CF(3)OCH(3)-CH(2)F(2), CF(3)OCF(3)-CH(2)F(2), CH(3)OCH(3)-CHF(3), CF(3)OCH(3)-CHF(3), and CF(3)OCF(3)-CHF(3) complexes were calculated by the MP2 level ab initio molecular orbital method using the 6-311G** basis set augmented with diffuse polarization functions. We investigate the fluorine substitution effects of both methane and dimethyl ether on intermolecular interactions. In addition, orientation dependence of intermolecular interaction energies is also studied with utilizing eight types of orientations. Our analyses demonstrate that partial fluorinations of methane make electrostatic interaction dominant, and consequently enhance attractive interaction at several specific orientations. On the contrary, fluorine substitutions of dimethyl ether substantially decrease the electrostatic interaction between ether and CH(2)F(2) or CHF(3); thus, there is no such characteristic interaction between the C-H of fluorinated methane and ether oxygen of CF(3)OCF(3) as conventional hydrogen bonding, due to reduced polarity of fluorinated ether. The combination of different pairs of the electrostatic interaction is therefore responsible for the intermolecular interaction differences among the complexes investigated herein and also their orientations.