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1.
Peroxy radicals and their derivatives are elusive but important intermediates in a wide range of oxidation processes. We observed pure rotational transitions of the water-hydroperoxy radical complex, H2O-HO2, in a supersonic jet by means of a Fourier transform microwave spectrometer combined with a double-resonance technique. The observed rotational transitions were found to split into two components because of the internal rotation of the water moiety. The molecular constants for the two components were determined precisely, supporting a molecular structure in which HO2 acts as a proton donor to form a nearly planar five-membered ring, and one hydrogen atom of water sticks out from the ring plane. The structure and the spectral splittings due to internal rotation provide information on the nature of the bonding interaction between open- and closed-shell species, and they also provide accurate transition frequencies that are applicable to remote sensing of this complex, which may elucidate its potential roles in atmospheric and combustion chemistry. 相似文献
2.
Sulfur difluioride has been identified and characterized from its microwave spectrum. The analysis of rotational transitions for both sulfur difluoride-32 and sulfur difluoride-34 shows that this molecular species has C(2v) symmetry with a bond length of 1.589 angstroms, a bond angle of 98 degrees 16', and a dipole moment of 1.05 Debye. 相似文献
3.
The rotational spectrum of a highly excited molecule is qualitatively different from its pure rotational spectrum and contains information about the intramolecular dynamics. We have developed a broadband Fourier transform microwave spectrometer that uses chirped-pulse excitation to measure a rotational spectrum in the 7.5- to 18.5-gigahertz range in a single shot and thereby reduces acquisition time sufficiently to couple molecular rotational spectroscopy with tunable laser excitation. After vibrationally exciting a single molecular conformation of cyclopropane carboxaldehyde above the barrier to C-C single-bond isomerization, we applied line-shape analysis of the dynamic rotational spectrum to reveal a product yield and picosecond reaction rate that were significantly different from statistical predictions. The technique should be widely applicable to dynamical studies of radical intermediates, molecular complexes, and conformationally flexible molecules with biological interest. 相似文献
4.
采用MPW1PW91/Aug-cc-pvqz方法及基组探索电场对OH自由基基态分子的总能量、键长、偶极矩、谐振频率、红外谱强度、电荷布居、HOMO和LUMO能级的影响.计算结果表明:MPW1PW91方法优化得到的核间距为Re=0.096 973nm,与实验值Re=0.096 96nm符合得非常好,只有0.001 3%的误差;振动频率为3 739.403cm~(-1),也与NIST数据库实验值3 737.76cm~(-1)一致;键长和红外谱强度随电场的增加先减小后增大;HOMO能和谐振频率分子总能量随电场的增加先增大后减小;偶极矩随电场增加线性地增加,LUMO能级随电场增加平缓地增加;E_g随外电场的增大先增大后减小.电场中OH自由基分子被激发至空轨道形成空穴时,该分子对电场强度具有选择性. 相似文献
5.
The first metal-xenon compound with direct gold-xenon bonds is achieved by reduction of AuF(3) with elemental xenon. The square planar AuXe(4)2+ cation is established by a single-crystal structure determination, with a gold-xenon bond length of approximately 274 picometers. The bonding between gold and xenon is of the final sigma donor type, resulting in a charge of approximately 0.4 per xenon atom. 相似文献
6.
Despite long study, a molecular picture of the mechanism of water reorientation is still lacking. Using numerical simulations, we find support for a pathway in which the rotating water molecule breaks a hydrogen bond (H-bond) with an overcoordinated first-shell neighbor to form an H-bond with an undercoordinated second-shell neighbor. The H-bond cleavage and the molecular reorientation occur concertedly and not successively as usually considered. This water reorientation mechanism involves large-amplitude angular jumps, rather than the commonly accepted sequence of small diffusive steps, and therefore calls for reinterpretation of many experimental data wherein water rotational relaxation is assumed to be diffusive. 相似文献
7.
Rotational spectra have traditionally been measured without a concurrent means of differentiating the molecular constituents of the sample. Here, we present an all-optical multipulse experiment that allows the correlated measurement of rotational and mass or photoelectron spectra by combining Fourier transform rotational coherence spectroscopy with resonance-enhanced multiphoton ionization. We demonstrate the power of this method with the determination of ground-state rotational constants and fragmentation channels for 10 different isotopes in a natural carbon disulfide sample. Three of the reported rotational constants were previously inaccessible by conventional spectroscopic techniques. 相似文献
8.
A monomeric arsinogallane containing a covalent gallium-arsenic bond has been prepared, and its molecular structure has been determined by x-ray crystallography. The compound reacted with tert-butanol at ambient temperature to yield the III-V semiconductor gallium arsenide as a finely divided amorphous solid. During the initial stages of the reaction small clusters of gallium arsenide were apparently present in solution. The band gaps of these particles, as observed by their absorption spectra, were larger than that of the bulk material. This work is a step toward the development of new molecular precursors for technologically important materials and the study of quantum size effects in small semiconductor particles. 相似文献
9.
Cruzan JD Braly LB Liu K Brown MG Loeser JG Saykally RJ 《Science (New York, N.Y.)》1996,271(5245):59-62
Measurement of the far-infrared vibration-rotation tunneling spectrum of the perdeuterated water tetramer is described. Precisely determined rotational constants and relative intensity measurements indicate a cyclic quasi-planar minimum energy structure, which is in agreement with recent ab initio calculations. The O-O separation deduced from the data indicates a rapid exponential convergence to the ordered bulk value with increasing cluster size. Observed quantum tunneling splittings are interpreted in terms of hydrogen bond rearrangements connecting two degenerate structures. 相似文献
10.
C L Coulter 《Science (New York, N.Y.)》1968,159(817):888-889
The crystal structure of the triethylammonium salt of cyclic uridine-3',5'-phosphate was solved by use of the tangent formula to refine phase angles based upon the positions of six of the atoms. The two independent uracil rings are planar and in the keto form. The base-sugar torsion angles are in the anti range. The sugar puckering is C3'-endo, and the ribose conformation about the C5'-C4' bond is transgauche. 相似文献
11.
Hawthorne MF Zink JI Skelton JM Bayer MJ Liu C Livshits E Baer R Neuhauser D 《Science (New York, N.Y.)》2004,303(5665):1849-1851
Rotary motion around a molecular axis has been controlled by simple electron transfer processes and by photoexcitation. The basis of the motion is intramolecular rotation of a carborane cage ligand (7,8-dicarbollide) around a nickel axle. The Ni(III) metallacarborane structure is a transoid sandwich with two pairs of carbon vertices reflected through a center of symmetry, but that of the Ni(IV) species is cisoid. The interconversion of the two provides the basis for controlled, rotational, oscillatory motion. The energies of the Ni(III) and Ni(IV) species are calculated as a function of the rotation angle. 相似文献
12.
Danzl JG Haller E Gustavsson M Mark MJ Hart R Bouloufa N Dulieu O Ritsch H Nägerl HC 《Science (New York, N.Y.)》2008,321(5892):1062-1066
Molecular cooling techniques face the hurdle of dissipating translational as well as internal energy in the presence of a rich electronic, vibrational, and rotational energy spectrum. In our experiment, we create a translationally ultracold, dense quantum gas of molecules bound by more than 1000 wave numbers in the electronic ground state. Specifically, we stimulate with 80% efficiency, a two-photon transfer of molecules associated on a Feshbach resonance from a Bose-Einstein condensate of cesium atoms. In the process, the initial loose, long-range electrostatic bond of the Feshbach molecule is coherently transformed into a tight chemical bond. We demonstrate coherence of the transfer in a Ramsey-type experiment and show that the molecular sample is not heated during the transfer. Our results show that the preparation of a quantum gas of molecules in specific rovibrational states is possible and that the creation of a Bose-Einstein condensate of molecules in their rovibronic ground state is within reach. 相似文献
13.
Lorenz KT Chandler DW Barr JW Chen W Barnes GL Cline JI 《Science (New York, N.Y.)》2001,293(5537):2063-2066
The preferred sense of product molecule rotation (clockwise or counterclockwise) in a bimolecular collision system has been measured. Rotationally inelastic collisions of nitric oxide (NO) molecules with Ar atoms were studied by combining crossed molecular beams, circularly polarized resonant multiphoton ionization probing, and velocity-mapped ion imaging detection. The observed sense of NO product rotation varies with deflection angle and is a strong function of the NO final rotational state. The largest preferences for sense of rotation are observed at the highest kinematically allowed product rotational states; for lower rotational states, the variation with deflection angle becomes oscillatory. Quantum calculations on the most recently reported NO-Ar potential give good agreement with the observed oscillation patterns in the sense of rotation. 相似文献
14.
根据有机化合物的构性相关规则 ,用演绎推理的方法建立了有机化合物构性相关分析的解析程序。这一解析程序把有机化合物的构性相关分析归纳成 5个步骤 ,即写出靶结构式 ,找出官能团 ,分析官能团和烃基中所含的每 1根化学键 ,考察分子中各结构单元之间产生的相互影响 ,最后分类总结出有机化合物的全部性能。 相似文献
15.
16.
Wang W Black SS Edwards MD Miller S Morrison EL Bartlett W Dong C Naismith JH Booth IR 《Science (New York, N.Y.)》2008,321(5893):1179-1183
How ion channels are gated to regulate ion flux in and out of cells is the subject of intense interest. The Escherichia coli mechanosensitive channel, MscS, opens to allow rapid ion efflux, relieving the turgor pressure that would otherwise destroy the cell. We present a 3.45 angstrom-resolution structure for the MscS channel in an open conformation. This structure has a pore diameter of approximately 13 angstroms created by substantial rotational rearrangement of the three transmembrane helices. The structure suggests a molecular mechanism that underlies MscS gating and its decay of conductivity during prolonged activation. Support for this mechanism is provided by single-channel analysis of mutants with altered gating characteristics. 相似文献
17.
Molecular metals normally require charge transfer between two different chemical species. We prepared crystals of [Ni(tmdt)2] (tmdt, trimethylenetetrathiafulvalenedithiolate) and carried out crystal structure analyses and resistivity measurements. The analyses and measurements revealed that these single-component molecular crystals are metallic from room temperature down to 0.6 kelvin. Ab initio molecular orbital calculations suggested that pi molecular orbitals form conduction bands. The compact molecular arrangement, intermolecular overlap integrals of the highest occupied and lowest unoccupied molecular orbitals, and tight-binding electronic band structure calculation revealed that [Ni(tmdt)2] is a three-dimensional synthetic metal composed of planar molecules. 相似文献
18.
Even in small molecules, the influence of electronic state on rotational and vibrational product energies is not well understood. Here, we use experiments and theory to address this issue in photodissociation of formaldehyde, H2CO, to the radical products H + HCO. These products result from dissociation from the singlet ground electronic state or the first excited triplet state (T1) of H2CO. Fluorescence spectra reveal a sudden decrease in the HCO rotational energy with increasing photolysis energy accompanied by substantial HCO vibrational excitation. Calculations of the rotational distribution using an ab initio potential energy surface for the T1 state are in very good agreement with experiment and strongly support dominance of the T1 state in the dynamics at the higher photolysis energies. 相似文献
19.
分子间的作用及其结构适应性 总被引：3，自引：0，他引：3
郭世豪 《湖南农业大学学报(自然科学版)》2001,27(2):148-150
某些分子间的作用无法的用范德华力、氢键、介电常数、偶极矩等化学基本理论来加以解释，引入控制论的方法对这些分析间的作用进行研究后的结果表明，选择性分析间引力很可能是分子是最强的物理作用，而分子间的化学作用亦与分子间的结构适应性密切相关。 相似文献
20.
以钛酸酯为前躯体,采用溶胶-凝胶法合成了TiO2改性的MQ硅树脂．就前躯体、MQ硅树脂及物料比对改性树脂热稳定性的影响进行了研究．同时,采用傅立叶红外光谱（Fourier Transform Infrared Spectrometer,FT-IR）对材料的分子结构进行了表征,采用热重分析（Thermogravimetric Aanlysis, TGA）对材料的热稳定性能进行了测试,采用扫描电镜（Scanning Electron Microscope, SEM）对材料的表面形貌进行了扫描．结果表明,TiO2改性MQ硅树脂体系中存在Ti-O-Si共价键;当m（钛酸异丙酯）：m（MQ硅树脂）=3：5时,改性树脂的热稳定性最佳;改性树脂粒子颗粒大小约为100nm左右． 相似文献