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.     

Experimental and theoretical ultraviolet spectra of haloindoles

The UV spectra of indole and the 4-, 5-, 6-, and 7-haloindoles (X=F, Cl, Br) have been recorded in methanol and calculated using time-dependent density functional theory. The lowest-energy UV absorption of each of the indoles is due to the HOMO-LUMO transition. This transition shifts to the red for the haloindoles relative to indole mainly as a result of the destabilization of the haloindole HOMOs.     

Vibrational spectra and density functional study of propylgermane

Raman and infrared spectra of propylgermane, CH₃CH₂CH₂GeH₃, and its Ge-deuterated analog, CH₃CH₂CH₂GeD₃, were investigated in their gaseous, liquid and solid states. The normal coordinate treatment was carried out by density functional theory (DFT) calculation, using B3LYP/6-31G^* and 6-311++G^** basis sets, and the corresponding fundamental vibrations were assigned. The trans (T) and gauche (G) forms around the central C–C bond coexisted in the gaseous and liquid states and only the T form existed in the solid state. From the temperature dependent measurements of the Raman spectra in the liquid state, the enthalpy difference was found to be ΔH(T−G)=−0.36±0.02 kcalmol⁻¹ with the T form being more stable. The energy differences between the isomers obtained by DFT calculations were ΔE(T−G)=−0.46 kcalmol⁻¹ and ΔE(T−G)=−0.87 kcalmol⁻¹ by the 6-31G^* basis set and 6-311++G^** basis set, respectively.     

Computational studies of the structure and vibrational spectra of hexafluorodisilane

Ab initio calculations predict that D_3d symmetry of Si₂F₆ is more stable than D_3h symmetry. The calculated potential barrier to internal rotation was 0.77, 0.73 and 0.78 kcal/mol using HF/6-31G*, B3LYP/6-31G* and MP2/6-31G* methods respectively, which was in good agreement with the experimental value between 0.51±0.10 and 0.73±0.14 kcal/mol. The optimized geometries, harmonic force fields, infrared intensities, Raman activities, and vibrational frequencies are reported for D_3d symmetry of Si₂F₆ from HF/6-31G* and B3LYP/6-31G*. A normal coordinate analysis was carried out. The average error between the scaled DFT frequencies obtained from the B3LYP/6-31G* calculation and observed frequencies was 4.2 cm⁻¹ and the average error between the scaled HF and observed frequencies was 2.2 cm⁻¹.     

Electronic absorption spectra and EPR spectra of irradiated silicate glasses

The election absorption spectra of sodium silicate glasses in the visible region and the EPR spectra of -irradiated two-component alkali silicate glasses have been studied. It has been established that the electron absorption spectra of these glasses have two bands in the visible region of the spectrum, while the EPR line with g=2.01 consists of two components. A comparison of the absorption spectral data with the EPR spectra showed that the band having a maximum around 4400 å and the -component of the doublet with g=2.01 are associated with the same hole center, of the type Si-O^–... Me⁺ while the band having a maximum around 6200 å and the -component of the doublet arise from a hole center of the type Si-O^–. The change in the ratio of the intensities of the - and -components with changes in the concentration and type of alkali metal is explained.     

Structure and vibrational spectra of the salts of mononitroalkanes

The molecular geometries of the anions of nitromethane and 2-nitropropane were optimised and their harmonic force fields were calculated by the RHF/6-311G(d,p), MP2/6-311G(d,p) and B3LYP/6-311G(d,p) methods. The force fields obtained made it possible to reliably interpret the IR and Raman spectra of the Na⁺ salt of nitromethane, d₂-nitromethane and 2-nitropropane. The assignment proposed significantly improves the interpretation of vibrational spectra known so far. Some general conclusions on geometry and vibrational spectra of the salts of mononitroalkanes studied are made. The hybrid density functional method used (B3LYP) is shown to be in better agreement with experimental data available than the Hartree–Fock methods.     

Si~2Cl~6分子的内旋转能垒和振动基频的理论研究

用从头算方法HF/6-31G^*^*和密度函方法B3LYP/6-31G^*^*,对Si~2Cl~6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si~2Cl~6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.18kJ/mol吻合得较好.对Si~2Cl~6分子的振动基频进行计算.用HF/6-31G^*^*SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^-^1,用B3LYP/6-31G^*^*未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^-^1.该密度泛函方法(B3LYP/~6-31G^*^*)的理论计算值比用HF/6-31G^*^*标度后的SQM力场计算的频率与实验值(除Si--Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si--Si键扭转振动基频的预测值。     

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n 相似文献   

Absorption spectra of thin film of polyaniline

The absorption spectra of thin film of polyaniline (PANI) on slide glass coated by a spin coater were measured as a function of the protonation state of PANI, the concentration of solution of PANI in NMP, drying temperature, and atmosphere. The absorbance value of the 950 nm peak and the ratio of the absorbance value at 950 nm to that of the 630 nm peak increases with increasing the protonation state of PANI. This is consistent with the observation of varying the conductivity with the protonation state. A modified molecular structure of PANI is proposed: where y and x are defined as the oxidation and the protonation states of PANI, respectively.     

FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular geometry of butylated hydroxy toluene

The FT-IR spectrum of 2,6-di-tert-butyl-4-methylphenol [butylated hydroxy toluene] was recorded in the region 4000-400 cm(-1). The FT-Raman spectrum of butylated hydroxy toluene was also recorded in the region 3500-50 cm(-1). The molecular structure and vibrational frequencies of butylated hydroxy toluene (BHT) have been investigated with combined experimental and theoretical study. Two stable conformers of the title compound were obtained from the result of geometry optimizations of these possible conformers. The conformer 1 is (approximately 2.6 kcal/mol) more stable than conformer 2. Geometry optimizations and vibrational frequency calculations were performed by BLYP and B3LYP methods using 6-31G(d), 6-31G(d,p) and 6-31+G(d,p) as basis sets. The scaled frequencies were compared with experimental spectrum and on the basis of this comparison; assignments of fundamental vibrational modes were examined. Comparison of the experimental spectra with harmonic vibrational wavenumbers indicates that B3LYP/6-31G(d) results are more accurate. Predicted electronic absorption spectra of BHT from TD-DFT calculation have been analyzed and compared with the experimental UV-vis spectrum. The calculated HOMO and LUMO energies show that the charge transfer occurs within the molecule.     

Photoelectron spectra and ion chemistry of imidazolide

The 351.1 nm photoelectron spectrum of imidazolide anion has been measured. The electron affinity (EA) of the imidazolyl radical is determined to be 2.613 +/- 0.006 eV. Vibrational frequencies of 955 +/- 15 and 1365 +/- 20 cm(-1) are observed in the spectrum of the (2)B1 ground state of the imidazolyl radical. The main features in the spectrum are well-reproduced by Franck-Condon simulation based on the optimized geometries and the normal modes obtained at the B3LYP/6-311++G(d,p) level of density functional theory. The two vibrational frequencies are assigned to totally symmetric modes with C-C and N-C stretching motions. Overtone peaks of an in-plane nontotally symmetric mode are observed in the spectrum and attributed to Fermi resonance. Also observed is the photoelectron spectrum of the anion formed by deprotonation of imidazole at the C5 position. The EA of the corresponding radical, 5-imidazolyl, is 1.992 +/- 0.010 eV. The gas phase acidity of imidazole has been determined using a flowing afterglow-selected ion tube; delta(acid)G298 = 342.6 +/- 0.4 and delta(acid)H298 = 349.7 +/- 0.5 kcal mol(-1). From the EA of imidazolyl radical and gas phase acidity of imidazole, the bond dissociation energy for the N-H bond in imidazole is determined to be 95.1 +/- 0.5 kcal mol(-1). These thermodynamic parameters for imidazole and imidazolyl radical are compared with those for pyrrole and pyrrolyl radical, and the effects of the additional N atom in the five-membered ring are discussed.     

Rovibrational spectra of bounded diatomic molecules

Spectra of a bounded diatomic molecule is studied numerically. Shifted Deng–Fan oscillator potential has been used to model the molecule. The accurate five‐point finite difference method has been used to solve the Schrödinger equation for rovibrational motion of the molecule. The energies of the bound states as well as free states of the molecule have been calculated. In addition, radial matrix elements like , n = 1, 2, and 3 have been calculated. These have been used to calculate the ‐pole static polarizabilities. The variation of bound state energies, matrix elements and ‐pole static polarizabilities with the boundary radius has also been studied. The Stark effect in case of this bounded system has also been investigated.     

Nuclear magnetic resonance spectra and structure of some alkyl vinyl sulphides

The NMR spectra of eight alkyl vinyl sulphides have been analyzed and the parameters compared with those obtained from an analogous series of oxygen derivatives. It is shown that a definite parallelism exists between chemical shifts and H? H coupling. Difference in absolute values have been explained by mesomeric interaction involving the ability of sulphur to accommodate a decet of electrons in its valence shell. By analogy with alkyl vinyl ethers, it is possible to predict a similar correlation between the spectral characteristics and relative reactivity of vinyl sulphides in cationic polymerization.     

Vibrational spectra and structure of cyclopentane and its isotopomers

The infrared and Raman spectra of vapor, liquid, and solid state cyclopentane and its d(1), 1,1-d(2), 1,1,2,2,3,3-d(6), and d(10) isotopomers have been recorded and analyzed. The experimental work was complemented by ab initio and density functional theory (DFT) calculations. The computations confirm that the two conformational forms of cyclopentane are the twist (C(2)) and bent (C(s)) structures and that they differ very little in energy, less than about 10 cm(-1) (0.1 kJ/mol). The bending angle for the C(s) form is 41.5° and the dihedral angle of twisting is 43.2° for the C(2) form. A reliable and complete vibrational assignment for each of the isotopomers has been achieved for the first time, and these agree very well with the DFT (B3LYP/cc-pVTZ) computations. The ab initio CCSD/cc-pVTZ calculations predict a barrier to planarity of 1887 cm(-1), which is in excellent agreement with the experimental value of 1808 cm(-1).     

NMR spectra, GIAO and charge density calculations of five-membered aromatic heterocycles

The B3LYP/6-31+G(d) molecular geometry optimized structures of 17 five-membered heterocycles were employed together with the gauge including atomic orbitals (GIAO) density functional theory (DFT) method at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p) and B3LYP/6-311+G(2d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants. The method of geometry optimization for pyrrole (1), N-methylpyrrole (2) and thiophene (7) using the larger 6-311++G(d,p) basis sets at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,p) and B3LYP/cc-pVTZ levels of theory gave little difference between calculated and experimental values of coupling constants. In general, the (1)H and 13C chemical shifts for all compounds are in good agreement with theoretical calculations using the smaller 6-31 basis set. The values of nJHH(n=3, 4, 5) and rmnJ(CH)(n=1, 2, 3, 4) were predicted well using the larger 6-31+G(d,p) and 6-311++G(d,p) basis sets and at the B3LYP/6-31+G(d,p), B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p) levels of theory. The computed atomic charges [Mülliken; Natural Bond Orbital Analysis (NBO); Merz-Kollman (MK); CHELP and CHELPG] for the B3LYP/6-311++G(d,p) geometry optimized structures of 1-17 were used to explore correlations with the experimental proton and carbon chemical shifts.     

Vibrational spectra and structure of sulfonium nitroimides

Vibrational spectroscopy and x-ray structure analysis have been used to investigate three new types of sulfonium nitroimides: N-nitrosulfylimides, N-nitrosulfoximides, and N,N-dinitrosulfodiimides. Structural parameters have been determined for the molecules , , and .Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2489–2496, November, 1991.     

Investigation of conformational stability and vibrational spectra of halomethylsulfonyl isocyanates

The conformational behavior and structural stability of chloro- and fluoromethylsulfonyl isocyanates were investigated by quantum mechanical DFT and ab initio MP2 calculations. The 6-311++G^** basis set was employed to include polarization and diffuse functions in the calculations. The molecules were found to exist in a mixture of two stable gauche conformations. The potential scans were calculated from which the rotational barriers could be estimated. The vibrational frequencies and spectra were computed at B3LYP/6-311++G^** level. The potential energy distributions were then calculated to provide tentative vibrational assignment for the normal modes of the stable conformers of both molecules.     

FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular conformational analysis of 2,5-di-tert-butyl-hydroquinone

The purpose of finding conformer among six different possible conformers of 2,5-di-tert-butyl-hydroquinone (DTBHQ), its equilibrium geometry and harmonic wavenumbers were calculated by the B3LYP/6-31G(d,p) method. The infrared and Raman spectra of DTBHQ were recorded in the region 400-4000 cm(-1) and 50-3500 cm(-1), respectively. In addition, the IR spectra in CCl(4) at various concentrations of DTBHQ are also recorded. The computed vibrational wavenumbers were compared with the IR and Raman experimental data. Computational calculations at B3LYP level with two different basis sets 6-31G(d,p) and 6-311++G(d,p) are also employed in the study of the possible conformer of DTBHQ. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA 4 program. The general agreement between the observed and calculated frequencies was established.     

DFT calculation and assignment of vibrational spectra of aryl and alkyl chlorophosphates

DFT calculations of vibrational spectra of chlorophosphates using wide range of basis sets and hybrid functionals were performed. Good agreement between calculated and experimental vibrational spectra was reached by the combination of non-empirical functional PBE0 with both middle and large basis sets. The frequencies of the stretching vibrations of the phosphate group calculated using semi-empirical functional B3LYP for all basis sets deviate significantly from the experimental values. The number of polarization functions on heavy atoms was shown to be a key factor for the calculation of vibrational frequencies of organophosphates. The importance of consideration of all the stable rotamers for a complete assignment of fundamental modes was shown.