共查询到20条相似文献,搜索用时 15 毫秒
1.
Maksim KunitskiStefan Knippenberg Andreas DreuwBernhard Brutschy 《Vibrational Spectroscopy》2011,56(1):13-18
1-Butene was investigated by rotational femtosecond degenerate four-wave mixing spectroscopy (fs DFWM) under supersonic expansion conditions as well as by quantum chemical calculations. Fs DFWM is a time-resolved rotational Raman spectroscopy, which allows for precise determination of rotational constants. The experimental fs DFWM spectrum was successfully reproduced by a fitted simulation using a single structure ascribed to the gauche conformer of 1-butene. The obtained rotational constants A = 22.6 ± 1.7 GHz, B = 4.1554 ± 0.0004 GHz and C = 4.0550 ± 0.0004 GHz are in excellent agreement with the ones from microwave spectroscopy. The cis conformer was not observed in the fs DFWM spectrum recorded under the low-temperature conditions of a supersonic expansion. The absence of the cis form along with simulations of a fs DFWM spectrum indicate that the cis conformer is at most equally but most likely less stable than the gauche rotamer. The experimental findings were supplemented by high level quantum chemical calculations, which predict the gauche form to have lower total energy than the cis structure. 相似文献
2.
Brügger G Frey HM Steinegger P Balmer F Leutwyler S 《The journal of physical chemistry. A》2011,115(34):9567-9578
We combine femtosecond time-resolved rotational coherence spectroscopy with high-level ab initio theory to obtain accurate structural information for the nonpolar molecules cyclohexane (C(6)H(12)) and cyclohexane-d(12) (C(6)D(12)). We measured the rotational B(0) and centrifugal distortion constants D(J), D(JK) of the v = 0 states of C(6)H(12) and C(6)D(12) to high accuracy, for example, B(0)(C(6)H(12)) = 4306.08(5) MHz, as well as B(v) for the vibrationally excited states ν(32), ν(6), ν(16) and ν(24) of C(6)H(12) and additionally ν(15) for C(6)D(12). To successfully reproduce the experimental RCS transient, the overtone and combination levels 2ν(32), 3ν(32), ν(32) + ν(6), and ν(32) + ν(16) had to be included in the RCS model calculations. The experimental rotational constants are compared to those obtained at the second-order M?ller-Plesset (MP2) level. Combining the experimental and calculated rotational constants with the calculated equilibrium bond lengths and angles allows determination of accurate semiexperimental equilibrium structure parameters, for example, r(e)(C-C) = 1.526 ± 0.001 ?, r(e)(C-H(axial)) = 1.098 ± 0.001 ?, and r(e)(C-H(equatorial)) = 1.093 ± 0.001 ?. The equilibrium C-C bond length of C(6)H(12) is only 0.004 ? longer than that of ethane. The effect of ring strain due to the unfavorable gauche interactions is mainly manifested as small deviations from the C-C-C, C-C-H(axial), and C-C-H(equatorial) angles from the tetrahedral value. 相似文献
3.
Kummli DS Lobsiger S Frey HM Leutwyler S Stanton JF 《The journal of physical chemistry. A》2008,112(38):9134-9143
We combine femtosecond time-resolved rotational coherence spectroscopy with high-level ab initio theory to obtain accurate structural information for the nonpolar antiaromatic molecule 1,3,5,7-cyclooctatetraene (C8H8, COT) and its perdeuterated isotopomer COT-d8 (C8D8). We measure the rotational B0 and centrifugal distortion constants D(J), D(JK) of the v = 0 states of COT and COT-d8 to high accuracy, e.g. B0 (COT) = 2710.329(56) MHz, as well as B(v) for the v = 1 states nu6, nu11, nu17, nu22, and nu41/nu42 of COT. The experimental rotational constants are compared to those obtained from calculations at the coupled-cluster with single, double, and perturbative triples [CCSD(T)] level. The latter also take into account vibrational averaging effects of the ground and vibrationally excited states. Combining the experimental and calculated rotational constants with the calculated equilibrium bond lengths and angles allows us to determine accurate equilibrium structure parameters, e.g., r(e) (C-C) = 147.0 +/- 0.05 pm, r(e) (C=C) = 133.7 +/- 0.1 pm, and r(e) (C-H) = 107.9 +/- 0.1 pm. The equilibrium C-C and C=C bond lengths of COT are compared to those of 1,3-butadiene. The expected effect of decreased pi-electron delocalization due to the twisting of adjacent C=C double bonds in COT relative to butadiene is observed for the C-C bonds but not for the C=C bonds. 相似文献
4.
The microwave rotational spectrum of propargyl benzene has been studied and its stable conformation has coplanar carbon atoms. This planar structure is confirmed independently by the value of its Pcc second moment consistent with only a pair of H atoms out of the plane, by its rotational spectrum obeying a- and b-type and not c-type selection rules, by its display of spectra of nine rather than six distinguishable monosubstituted 13C isotopomers, by the absence of tunneling splittings, and by the insensitivity of Pcc to 13C isotopic substitution. This conformation is also observed in its isoelectronic analogue, benzyl cyanide. The structure is stabilized by an effective hydrogen bond between an ortho C-H and the π electrons of the triple bond. 相似文献
5.
A highly accurate combined experimental and theoretical investigation has been conducted on p-toluidine (4-methylaniline) in its vibrational and electronic ground state. 相似文献
6.
Structural phase transition and 5f-electrons localization of PuSe explored by ab initio calculations
An investigation into the structural phase transformation, electronic and optical properties of PuSe under high pressure was conducted by using the full potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method, in the presence and in the absence of spin-orbit coupling (SOC). Our results demonstrate that there exists a structural phase transition from rocksalt (B 1) structure to CsCl-type (B 2) structure at the transition pressure of 36.3 GPa (without SOC) and 51.3 GPa (with SOC). The electronic density of states (DOS) for PuSe show that the f-electrons of Pu are more localized and concentrated in a narrow peak near the Fermi level, which is consistent with the experimental studies. The band structure shows that B 1-PuSe is metallic. A pseudogap appears around the Fermi level of the total density of states of B 1 phase PuSe, which may contribute to its stability. The calculated reflectivity R(ω) shows agreement with the available experimental results. Furthermore, the absorption spectrum, refractive index, extinction coefficient, energy-loss spectrum and dielectric function were calculated. The origin of the spectral peaks was interpreted based on the electronic structures. 相似文献
7.
Natural sphalerite samples collected from the Baia Sprie ore deposit (Romania) were analyzed through Raman spectroscopy, SEM-EDX and XRD. The most intense Raman lines at 300, 331 and 350 cm−1 were used to improve iron determination method from sphalerites by Raman spectroscopy. It is well known that the iron content of synthetic sphalerite can be quantified by measuring the height of Raman lines (h1, h3). By using the new h2/h3 and (h1 + h2)/h3 ratios and two additional linear equations, this method is improved and becomes suitable to natural sphalerites. The results are in good agreement with the SEM-EDX data. 相似文献
8.
The crystal structure of metastable Li2Si3O7 was determined from single crystal X-ray diffraction data. The orthorhombic crystals were found to adopt space group Pmca with unit cell parameters of , and . The content of the cell is Z=4. The obtained structural model was refined to a R-value of 0.035. The structure exhibits silicate sheets, which can be classified as [Si6O14] using the silicate nomenclature of Liebau. The layers are build up from zweier single chains running parallel to c. Raman spectra are presented and compared with other silicates. Furthermore, the structure is discussed versus Na2Si3O7. 相似文献
9.
The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective. 相似文献
10.
Silvère André Lydia Saint Cristau Sabine Gaillard Olivier Devos Éric Calvosa Ludovic Duponchel 《Analytica chimica acta》2015
The Food and Drug Administration's (FDA) process analytical technology (PAT) framework has been initiated to encourage drug manufacturers to develop innovative techniques in order to better understand their processes and institute high level quality control which allows action at any point in the manufacturing process. While Raman spectroscopy and chemometrics have been successfully used to predict concentration of conventional metabolites in cell cultures, it is really not the case for active substances. Thus, we propose, for the first time, an in-line and real-time prediction of recombinant antibody titer using an immersion probe link to a spectrometer without the tacking of samples. A good robustness of the method is observed on different culture batches and the contamination risk is drastically reduced which is an important issue in biotechnology manufacturing processes. 相似文献
11.
Zhang YH Guo L Yin PG Zhang R Zhang Q Yang SH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(10):2903-2907
A highly regular hexapod-like structure of PbS with six symmetric arms has been synthesized by a simple and mild chemical solution route. The hexapod-like PbS structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The results show that each arm is perpendicular to the other four, and opposite to the last one. The arms are about 0.3-0.6 microm long, which have about 40-60 nm tips and 150-200 nm base. And the arm shows an icicle-like structure and some clear steps, and grows along 100 directions. The most possible growth mechanism discussed herein is based on the characterization results. The Raman spectra of the hexapod-like PbS structure were investigated. The results show that our products are sensitive to the laser and can be photodegraded easily. 相似文献
12.
We have investigated the molecular structure and conformation of diethylmethylamine, C(4)H3C(2)H2N(1)[CH3]C(3)H2C(5)H3, by gas electron diffraction and vibrational spectroscopy with the aid of theoretical calculations. Diffraction data are consistent with a conformational mixture of 35(14)% tt + 27(14)% g+t + 20(17)% g−t + 18(23)% g+g+ where the numbers in parentheses denote three times the standard errors (3σ). Normal-coordinate analysis based on B3LYP/6-311+G** calculations supports the existence of the four conformers. The dihedral angle 1(C4C2N1C3) (= −2(C5C3N1C2)) of the tt conformer was 170(4)° whereas the 1 and 2 values of the other conformers were fixed at the B3LYP/6-311++G(2df,p) values: 72.4° and −163.3° for the g+t, −66.0° and −158.2° for the g−t, and 60.3° and 63.5° for the g+g+. Average values of the structural parameters (rg/Å and α/°) with 3σ are: r(N–C) = 1.462(2), r(C–C) = 1.523(3), r(C–H) = 1.113(2), CNC = 111.6(5), NCC = 114.5(5), NCH/CCHMe = 110.6(5). 相似文献
13.
Hiroshi Kojima Kosaku Sakeda Teijiro Ichimura Masao Takayanagi 《Journal of Molecular Structure》2003,655(1):185-190
Laser-induced fluorescence (LIF) excitation spectra of m-methylanisole in a supersonic jet were measured. Two series of progressions were observed in the spectrum, originating at 36048 and 36115 cm−1, which were successfully assigned to the transitions to the methyl internal rotational vibronic levels of the two isomers, i.e. cis and trans isomers, with the aid of hole-burning spectrum measurements and quantum-chemical calculations. The progression for the trans isomer was observed up to the 6a1 band, while only the 3a1 band in addition to the 0a1 and 1e bands was observed for the cis isomer. This finding can be explained by the conformational change upon the electronic excitation; the 60° rotation of the methyl torsional angle takes place for the trans isomer but not for the cis isomer. 相似文献
14.
Heavy atom structure and conformer stabilities of cyclopropyl carbinol from rotational spectroscopy and ab initio calculations 总被引:1,自引:0,他引:1
Josh J. Newby Rebecca A. Peebles Sean A. Peebles 《Journal of Molecular Structure》2005,740(1-3):133-142
A remeasurement of the rotational spectra of the normal and hydroxyl deuterated isotopomers of cyclopropyl carbinol (cyclopropane methanol, (CH2)2CH(CH2OH)) using Fourier-transform microwave spectroscopy has provided refined rotational constants and centrifugal distortion constants for this molecule. Rotational constants for an additional four singly substituted 13C isotopomers, the OD isotopomer, and the 18O isotopomer are consistent with a conformer in which the OH group forms an intramolecular hydrogen bond with the edge of the cyclopropyl ring. The observed a-type transition frequencies for the normal and deuterated species are in reasonable agreement with a previous microwave study (although some frequencies differ by several hundred kilohertz), but the few b- and c-type lines that were measured in the range of our spectrometer were found to differ by several megahertz from the previous literature measurements, leading to A rotational constants that differ significantly from those reported previously. The refined rotational constants for the normal isotopic species are A=12470.7795(23) MHz, B=3236.4678(7) MHz, C=2894.4831(7) MHz, while those of the deuterated species are A=12069.2653(24) MHz, B=3177.1540(8) MHz and C=2826.2658(7) MHz. Results of ab initio optimizations on seven conformers for this molecule carried out at the MP2/6-311+G(d,p) level will be compared with the experimentally determined structural parameters. 相似文献
15.
Evan G. Robertson Danielle E. Martin Chris D. Thompson Richard J.S. Morrison John G. Philis 《Chemical physics letters》2008,463(1-3):29-32
Sec-butylbenzene has been investigated using resonant two-photon ionization (R2PI) and UV–UV hole-burning spectroscopy aided by ab initio calculations. All three conformers predicted from theory are observed in the spectrum, and are assigned by rotational band contour analysis. The most strongly populated conformer (G1) has a gauche arrangement of the side chain dihedral angle τ2(C1CαCβCγ). The populations of the anti (A) and the remaining gauche conformer (G2) are about 7% and 2%, respectively. The alpha methyl group is found to significantly affect the conformational preferences in sec-butylbenzene (sec-BB), compared to n-propylbenzene in which the anti conformer is favored. 相似文献
16.
Studies of the surface wettability and hydrothermal stability of methyl-modified silica films by FT-IR and Raman spectra 总被引:1,自引:0,他引:1
Fourier transform infrared (FT-IR) and Raman spectroscopy were employed to study the hydrothermal stability and the influence of surface functional groups on the surface wettability of methyl-modified silica films. The surface free energy parameters of the silica films were determined using the Lifshitz-van der Waals/acid–base approach. The thermal decomposition mechanisms of the CH3 groups in the methyl-modified silica material are proposed. The results show that with the increase of methyltriethoxysilane (MTES)/tetraethylorthosilicate (TEOS) ratio, the surface free energy and surface wettability of the silica films decrease greatly. This is mainly because of the contribution of the acid–base term; the intensity of Si–CH3 groups increases at the expense of the intensity of O–H groups in the samples. The surfaces of the methyl-modified silica films exhibited predominantly monopolar electron-donicity. The contact angle on the silica film surface reaches its maximum value when calcination is performed at 350 °C. Thermogravimetric analysis implies that some low molecular weight species, such as H2, CH4, and C, are eliminated upon thermal decomposition of the –CH3 groups. The Si–CH3 and –CH3 vibrational bands diminish in intensity as the calcination temperature is increased, disappearing completely when the calcination temperature is increased to 600 °C. When the calcination temperature is increased to 750 °C, the free carbon and CSi4 species will be formed. 相似文献
17.
《Angewandte Chemie (International ed. in English)》2017,56(16):4392-4430
Raman spectroscopy is an emerging technique in bioanalysis and imaging of biomaterials owing to its unique capability of generating spectroscopic fingerprints. Imaging cells and tissues by Raman microspectroscopy represents a nondestructive and label‐free approach. All components of cells or tissues contribute to the Raman signals, giving rise to complex spectral signatures. Resonance Raman scattering and surface‐enhanced Raman scattering can be used to enhance the signals and reduce the spectral complexity. Raman‐active labels can be introduced to increase specificity and multimodality. In addition, nonlinear coherent Raman scattering methods offer higher sensitivities, which enable the rapid imaging of larger sampling areas. Finally, fiber‐based imaging techniques pave the way towards in vivo applications of Raman spectroscopy. This Review summarizes the basic principles behind medical Raman imaging and its progress since 2012. 相似文献
18.
W. Jeremy Jones Dale K. Thomas Daniel W. Thomas Graham Williams 《Journal of Molecular Structure》2004,708(1-3):145-163
Traditional approaches to the use of Raman spectroscopy as an aid to the determination of local order parameters in liquid crystalline materials have employed polarizations of the excitation source and/or the analyser which are orthogonal to the liquid crystalline director. The present paper describes a Raman study, which seeks to take advantage of the additional information available from examining the complete range of orientations of the director in relation to these polarization directions. A theory is developed which shows how it is possible to use this additional information to derive more reliable values of the P2 and P4 local order parameters in homogeneous and twisted nematic liquid crystal cells. 相似文献
19.