BrCl紫外光电子能谱实验及理论研究

采用紫外光电子能谱研究了影响大气臭氧浓度的重要卤素互化物一氯化溴的精细电离能谱．实验得到BrCl的第一绝热电离能和垂直电离能分别为10．95eV和11．00eV．BrCl的最高占据轨道6π电离产生了明显的旋轨分裂谱带．这对旋轨分裂谱带分别清晰地显示出4个振动精细结构峰．频率分析显示BrCl分子最高占据轨道为弱反键性质．比较了HF方法和外壳层格林函数方法(OVGF)对电离能的计算结果,并对实验值进行了分析比较及指认．采用实验构型OVGF方法给出的电离能结果无论在低电离能区还是在高电离能区都和实验值一致,特别是第一垂直电离能10．988eV与实验值11．00eV非常好地吻合．     

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。     

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。     

利用紫外光电子能谱-质谱研究CF3自由基的大气光化学反应

利用建立的光化学反应装置和自行研制的紫外光电子能谱-光电离质谱(PES-PIMS),对CF3自由基与O2和CO的光化学反应进行了研究.对不稳定物种CF3OC(O)OOC(O)OCF3的电子结构以及电离解离的机理进行了分析研究.结果表明,CF3OC(O)OOC(O)OCF3的光电子能谱上出现的两个谱带分别来源于氧原子的孤对电子和CF3基团上F原子的孤对电子的电离,其中前者比后者更容易电离.实验得到CF3OC(O)OOC(O)OCF3的第一垂直电离能为13.21eV,而利用OVGF方法得到的计算值为13.178eV,二者吻合很好.结合光电离质谱,发现在HeI紫外光辐射下,CF3OC(O)OOC(O)OCF3发生一次电离后,母体离子通过C—O键的断裂发生异裂,随后形成碎片离子CF3OCO 和CF3 .研究表明,结合光化学反应装置的紫外光电子能谱-光电离质谱有望在瞬态物种的大气光化学反应研究中得到广泛应用.     

XNCS→XSCN (X=Cl,Br)异构化的实验与量子化学研究

捕获得到了纯净化合物ClSCN和BrSCN紫外光电子能谱图,OVGF方法计算的ClSCN和BrSCN的电离能与实验值吻合很好,并用该方法首次预测了ClNCS和BrNCS的电离能．讨论了XNCS→XSCN(X=Cl,Br)的异构化过程,首次优化得到了四元环过渡态的构型．着重从电子密度拓扑分析计算了反应进程中的各点,讨论了反应进程中键的断裂和生成,上述反应都经历了三元环过渡结构,找到了这类反应的“能量过渡态”和“结构过渡态”．     

苯并噻唑衍生物的气相HeI紫外光电子能谱(UPS)及量子化学研究

对苯并噻唑系列衍生物的气相HeI紫外光电子能谱(UPS)进行了研究．首次报道 了五种化合物的紫外光电子能谱，利用Gaussian94从头算的量子化学计算方法对其 进行了计算，并结合计算结果对各个分子体系的谱图进行了指认．研究结果表明： 分子的电离能受取代基性质的影响，取代基的给电子能力越大，体系的共轭效应越 强，电离能就越低．对苯并噻唑衍生物而言，6-位取代基对电离能的影响大于2-位 取代基的影响．     

SiBr~4及其不同离子态的电子结构研究: 紫外光 电子能谱(PES)和理论研究

本文详细报道了SiBr~4的紫外光电子能谱(PES)及该化合物不同离子态(X^2T~2,A^2T~1,B^2E,C^2T~2等)的电子结构和性质。实验测得对应基态离子态的绝热电离能I~a(X^2T~2←X^1A~1)=10.532eV,X^2T~2离子态的振动频率为(450±30)cm^-^1。结合理论计算对紫外光电子能谱进行了指认和分析,结果表明X^2T~2,A~2T~1两个离子态存在明显的自旋-轨道耦合作用,自旋-轨道耦合导致的分裂分别为：0.27ev和0.53eV。此外,不同计算方法比较显示外层格林函数方法计算得到电离能与实验吻合很好。     

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.     

o-，m-，p-IC6H4OCH3的电子结构和取代基效应

采用紫外光电子能谱（UPS）手段结合理论计算研究了有机卤化物o-,m-,p-IC6H4OCH3的电子结构和取代基效应．在碘原子和甲氧基两个供电子基团的共同作用下,这三种碘代苯甲醚的第一电离能均低于相应的碘苯和苯甲醚．通过取代基效应研究表明碘代苯甲醚为富电子体,因此在有机合成反应中具有较高的反应活性．     

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。     

Theoretical determinations of ionization potentials of dopamine

Adiabatic and vertical ionization potentials (IPs) of nine conformers of dopamine in the gas phase are determined using density functional theory (DFT) B3LYP, B3P86, B3PW91 methods and high level ab initio HF method with 6-311++G** basis set, respectively. And the nine stable cationic states have been found in the ionization process of dopamine. Vertical ionization potentials of nine conformers of dopamine are calculated using the older outer-valence Green’s function (OVGF) calculations at 6-311++G** basis set. Vibrational frequencies and infrared spectrum intensities of G1b and G1b⁺ at B3LYP/6-311++G** level are discussed.     

An ab initio correlated study of the potential energy surface for the HOBr.H2O complex

The potential energy surface (PES) for the HOBr.H(2)O complex has been investigated using second- and fourth-order M?ller-Plesset perturbation theory (MP2, MP4) and coupled cluster theory with single and doubles excitations (CCSD), and a perturbative approximation of triple excitations (CCSD-T), correlated ab initio levels of theory employing basis sets of triple zeta quality with polarization and diffuse functions up to the 6-311++G(3dp,3df ) standard Pople's basis set. Six stationary points being three minima, two first-order transition state (TS) structures and one second-order TS were located on the PES. The global minimum syn and the anti equilibrium structure are virtually degenerated [DeltaE(ele-nuc) approximately 0.3 kcal mol(-1), CCSD-T/6-311++G(3df,3pd) value], with the third minima being approximately 4 kcal mol(-1) away. IRC analysis was performed to confirm the correct connectivity of the two first-order TS structures. The CCSD-T/6-311++G(3df,3pd)//MP2/6-311G(d,p) barrier for the syn<-->anti interconversion is 0.3 kcal mol(-1), indicating that a mixture of the syn and anti forms of the HOBr.H(2)O complex is likely to exist.     

Reaction of AgN3 with SOCl2: evidence for the formation of thionyl azide, SO(N3)2

Pure thionyl azide SO(N(3))(2), which is the only gaseous reaction product, has been generated in a vacuum by the heterogeneous reaction of SOCl(2) vapor with AgN(3) at room temperature at a SOCl(2) vapor pressure of 1 x 10(-3) Torr. Evidence for the formation of SO(N(3))(2) is given by on line photoelectron spectroscopy (PES) combined with outer valence Green's function (OVGF) calculations with the 6-311++G(2df) basis set. The good agreement between the PES experiment and the OVGF calculation shows that SO(N(3))(2) has C(1) symmetry. The first ionization energy of SO(N(3))(2) is 10.18 eV.     

Photoelectron spectra and electronic structures of some chlorosulfonyl pseudohalides

The electronic structures of chlorosulfonyl pseudohalide ClSO2X (X = Cl, NCO, N3) are studied by photoelectron spectroscopy (PES) combined with the OVGF calculation at 6-311++G(3df) basis sets. The first ionization potentials for ClSO2NCO and ClSO2N3 are determined to be 12.02 and 11.43 eV, respectively, for the first time, and their features in the PE spectra were assigned based on comparison with related compounds and with high level quantum calculations. Photoelectron spectra of ClSO2NCO and ClSO2N3 suggest that the interactions between chlorine "lone-pair" electrons and two pseudohalogen groups have significant effect on the HOMOs of two compounds, besides the influence of their electronegativity on the first ionization energies.     

He I photoelectron spectroscopy and theoretical investigation on diaceto disulfide, CH3C(O)OSSOC(O)CH3

A novel species, diaceto disulfide (CH3C(O)OSSOC(O)CH3), has been generated through the heterogeneous reaction between sulfur monochloride (S2Cl2) and silver acetate (AgOC(O)CH3). Photoelectron spectroscopy (PES) and theoretical calculations are performed to investigate its electronic and geometric structures. This molecule exhibits gauche conformation with both C=O groups syn to the S-O bond. The dihedral angle around the S-S bond is calculated to be -93.1 degrees at the B3LYP/6-311++G(3df,3pd) level. After structural optimizations of the most stable conformer, a theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) was performed. The ionization energies of different bands in the photoelectron spectrum are in good agreement with the calculated values from the OVGF method. The first vertical ionization energy of CH3C(O)OSSOC(O)CH3 is determined to be 9.83 eV by photoelectron spectroscopy, which corresponds to the ionization of an electron mainly localized on the sulfur 3p lone pair molecular orbital.     

Computational Exploration of Conformations of Glycine-Arginine and a Deduced Model on Global Minimum Configurations of Dipeptides in Gas Phase

An extensive computational study on the conformations of gaseous dipeptide glycinearginine, GlyArg, has been performed. A large number of trail structures were generated by systematically sampling the potential energy surface (PES) of GlyArg. The trial structures were successively optimized with the methods of PM3, HF/3-21G^*, BHandHLYP/6-31G^*, and BHandHLYP/6-311++G^** in order to reliably find the low energy conformations. The conformational energies were finally determined with the methods of BHandHLYP, camB3LYP, B97D, and MP2 using the basis set of 6-311++G(3df,3pd). The results establish firmly that gaseous GlyArg exists primarily in its canonical form, in sharp contrast with ArgGly that adopts the zwitterionic form. Important data such as the rotational constants, dipole moments, vertical ionization energies, temperature distributions and IR spectra of the low energy conformers are represented for the understanding of the future experiments. Moreover, considering the global minima of all amino acids and many dipeptides, combined with the hydrophobicities of amino acids, a model predicting whether the global minimum configuration of a dipeptide is canonical or zwitterionic is developed.     

Comparison of some representative density functional theory and wave function theory methods for the studies of amino acids

Energies of different conformers of 22 amino acid molecules and their protonated and deprotonated species were calculated by some density functional theory (DFT; SVWN, B3LYP, B3PW91, MPWB1K, BHandHLYP) and wave function theory (WFT; HF, MP2) methods with the 6-311++G(d,p) basis set to obtain the relative conformer energies, vertical electron detachment energies, deprotonation energies, and proton affinities. Taking the CCSD/6-311++G(d,p) results as the references, the performances of the tested DFT and WFT methods for amino acids with various intramolecular hydrogen bonds were determined. The BHandHLYP method was the best overall performer among the tested DFT methods, and its accuracy was even better than that of the more expensive MP2 method. The computational dependencies of the five DFT methods and the HF and MP2 methods on the basis sets were further examined with the 6-31G(d,p), 6-311++G(d,p), aug-cc-pVDZ, 6-311++G(2df,p), and aug-cc-pVTZ basis sets. The differences between the small and large basis set results have decreased quickly for the hybrid generalized gradient approximation (GGA) methods. The basis set convergence of the MP2 results has been, however, very slow. Considering both the cost and the accuracy, the BHandHLYP functional with the 6-311++G(d,p) basis set is the best choice for the amino acid systems that are rich in hydrogen bonds.     

DFT-GIAO calculations of 19F NMR chemical shifts for perfluoro compounds

The (19)F NMR shieldings for 53 kinds of perfluoro compounds were calculated by the B3LYP-GIAO method using the 6-31G(d), 6-31+G(d), 6-31G(d,p), 6-31++G(d,p), 6-311G(d,p), 6-311++G(d,p), 6-311G(2d,2p), 6-311++G(2d,2p), 6-311++G(2df,2p), 6-311++G(3d,2p), and 6-311++G(3df,2p) basis sets. The diffuse functions markedly reduce the difference between the calculated and experimental chemical shifts. The calculations using the 6-31++G(d,p) basis set give the chemical shifts within 10 ppm deviations from experimental values except for the fluorine nuclei attached to an oxygen atom, a four- and a six-coordinated sulfur atom, and FC(CF(3))(2) attached to a sulfur atom.     

An exploration of conformational search of leucine molecule and their vibrational spectra in gas phase using ab initio methods

An extensive exploration of the conformational space has been carried out to characterize all possible gas phase structures of leucine. A total of 324 unique trial structures for canonical leucine were generated by considering all possible combinations of single bond rotamers. All trial structures were optimized at the B3LYP/6-311G* level of the DFT method. A total of 77 unique and stationary canonical conformers were found. Further, 15 most stable conformers were reoptimized at B3LYP/6-311++G** level and their respective relative energies, vertical ionization energies, hydrogen bonding patterns, rotational constants and dipole moments were calculated. A single point energy calculations for leucine conformers have also been done at both B3LYP/6-311++G(2df, p) and MP2/6-311++G(2df, p) levels. The good agreement between our estimates of rotational constants for two most stable conformers and available experimental measurements supports the reliability of the B3LYP/6-311++G** level of theory for describing the conformational behavior of leucine molecule. The proton affinity and gas phase basicity were also determined. Using the statistical approach, conformational distributions at various temperatures have also been performed and analyzed. Vibrational spectra were also calculated. It is also observed that zwitterions of leucine are not stable in gas phase.     

Microwave spectrum of 3-butyne-1-thiol: evidence for intramolecular S-H...pi hydrogen bonding

The microwave spectrum of 3-butyne-1-thiol has been studied by means of Stark-modulation microwave spectroscopy and quantum-chemical calculations employing the B3LYP/6-311++G(3df,2pd), MP2/aug-cc-pVTZ, MP2/6-311++G(3df,2pd), and G3 methods. Rotational transitions attributable to two conformers of this molecule were assigned. One of these conformers possesses an antiperiplanar arrangement of the atoms S-C1-C2-C3, while the other is synclinal and stabilized by the formation of an intramolecular hydrogen bond between the H-atom of the thiol group and the pi-electrons of the C[triple bond]C triple bond. The energy difference between these conformers was estimated to be 1.7(4) kJ mol(-1) by relative intensity measurements, with the hydrogen-bonded conformer being lower in energy. The spectra of five vibrationally excited states of the synclinal conformer were observed, and an assignment of these states to particular vibrational modes was made with the aid of a density functional theory (DFT) calculation of the vibrational frequencies at the B3LYP/6-311++G(3df,2pd) level of theory.