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排序方式: 共有151条查询结果,搜索用时 15 毫秒
71.
Benniston AC Harriman A Li P Patel PV Sams CA 《The Journal of organic chemistry》2006,71(9):3481-3493
The synthesis of a series of binuclear complexes comprising bis(2,2':6',2' '-terpyridine)ruthenium(II) and -osmium(II) centers connected via a geometrically constrained 4,4'-biphenyl bridge is described. These compounds have been prepared by a "synthesis-at-metal" approach as well as by the conventional method of synthesizing the ligand and subsequently attaching the metal center. A computational investigation into the behavior of the biphenyl-based bridges has been used to provide lowest-energy conformations and to estimate the degree of internal fluctuation about the mean torsion angle. It is shown that the length of the constraining strap determines both the torsion angle and the internal flexibility, with longer straps twisting the biphenyl group so as to relax stereochemical interactions between the linking oxygen atoms. Longer straps can be formed from poly(ethylene glycol) residues that provide an additional binding site for small cations. Electrospray mass spectrometry carried out on solutions of these crown ether-like bridges confirmed that Li+, Na+, and K+ ions bind in the form of 1:1 complexes. This range of compounds should permit rational examination of how the torsion angle affects the rate of through-bond electron transfer, electron exchange, and charge shift. 相似文献
72.
The Fourier transform infrared spectrum of tropolone(OH) vapor in the 1175-1700 cm(-1) region is reported at 0.0025 and 0.10 cm(-1) spectral resolutions. The 12 vibrational fundamentals in this region of rapidly rising vibrational state density are dominated by mixtures of the CC, CO, CCH, and COH internal coordinates. Estimates based on the measurement of sharp Q branch peaks are reported for 11 of the spectral doublet component separations DS(v) = |Delta(v) +/- Delta(0)|. Delta(0) = 0.974 cm(-1) is the known zero-point splitting, and three a(1) modes show tunneling splittings Delta(v) approximately Delta(0), four b(2) modes show splittings Delta(v) approximately 0.90Delta(0), and the remaining four modes show splittings Delta(v) falling 5-14% from Delta(0.) Significantly, the splitting for the nominal COH bending mode nu(8) (a(1)) is small, that is, 10% from Delta(0). Many of the vibrational excited states demonstrate strong anharmonic behavior, but there are only mild perturbations on the tautomerization mechanism driving Delta(0). The data suggest, especially for the higher frequency a(1) fundamentals, the onset of selective intramolecular vibrational energy redistribution processes that are fast on the time scale of the tautomerization process. These appear to delocalize and smooth out the topographical modifications of the zero-point potential energy surface that are anticipated to follow absorption of the nu(v) photon. Further, the spectra show the propensity for the Delta(v) splittings of b(2) and other complex vibrations to be damped relative to Delta(0). 相似文献
73.
Fourier transform spectra of mono-13C ethylene have been recorded in the 8.4-14.3-μm spectral region (700-1190 cm−1) using a Bruker 120 HR interferometer at a resolution of 0.0017 cm−1 allowing the extensive study of the set of resonating states {101, 81, 71, 41, 61}. Due to the high resolution available as well as the extended spectral range involved in this study, a much larger set of line assignments are now available. The present analysis has lead to the determination of more accurate spectroscopic constants, including interaction constants, than were obtained in earlier studies. In particular, the following band centers were derived: ν0(ν10) = 825.40602(30) cm−1, ν0(ν8) = 932.19572(15) cm−1, ν0(ν7) = 937.44452(10) cm−1, ν0(ν4) = 1025.6976(14) cm−1. Finally a synthetic spectrum was generated leading to the assignment of a number of 13C12CH4 lines observed in an earlier heterodyne spectroscopic study. 相似文献
74.
Norman C. Craig Matthew C. Leyden Amie K. Patchen Thomas A. Blake Robert L. Sams 《Journal of Molecular Spectroscopy》2010,262(1):49-60
Assignments of the vibrational fundamentals of cis- and trans-1,3,5-hexatriene are reevaluated with new infrared and Raman spectra and with quantum chemical predictions of intensities and anharmonic frequencies. The rotational structure is analyzed in the high-resolution (0.0013-0.0018 cm−1) infrared spectra of three C-type bands of the trans isomer and two C-type bands of the cis isomer. The bands for the trans isomer are at 1010.96 cm−1 (ν14), 900.908 cm−1 (ν16), and 683.46 cm−1 (ν17). Ground state (GS) rotational constants have been fitted to the combined ground state combination differences (GSCDs) for the three bands of the trans isomer. The bands for the cis isomer are at 907.70 cm−1 (ν33) and 587.89 cm−1 (ν35). GS rotational constants have been fitted to the combined GSCDs for the two bands of the cis isomer and compared with those obtained from microwave spectroscopy. Small inertial defects in the GSs confirm that both molecules are planar. Upper state rotational constants were fitted for all five bands. 相似文献
75.
V. Malathy Devi D. Chris Benner C.P. Rinsland M.A.H. Smith R.L. Sams T.A. Blake Jean-Marie Flaud Keeyoon Sung L.R. Brown A.W. Mantz 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(17-18):2481-2504
Ethane is a prominent contributor to the spectrum of Titan, particularly in the ν9 region centered near 822 cm?1. To improve the spectroscopic line parameters at 12 μm, 41 high-resolution (0.0016–0.005 cm?1) absorption spectra of C2H6 were obtained at sample temperatures between 211 and 298 K with the Bruker IFS 120HR at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington. Two additional spectra were later recorded at ~150 K using a new temperature-stabilized cryogenic cell designed for the sample compartment of the Bruker IFS 125HR at the Jet Propulsion Laboratory (JPL) in Pasadena, California. A multispectrum nonlinear least-squares fitting program was applied simultaneously to all 43 spectra to measure the line positions, intensities, N2- and self-broadened half-width coefficients and their temperature dependences. Reliable pressure-induced shift coefficients could not be obtained, however, because of the high congestion of spectral lines (due to torsional-split components, hot-band transitions as well as blends). Existing theoretical modeling of this very complicated ν9 region permitted effective control of the multispectrum fitting technique; some constraints were applied using predicted intensity ratios, doublet separations, half-width coefficients and their temperature dependence exponents in order to determine reliable parameters for each of the two torsional-split components. For 12C2H6, the resulting retrievals included 17 pQ and rQ sub-bands of ν9 (as well as some pP, rR sub-bands). Positions and intensities were measured for 3771 transitions, and a puzzling difference between previously measured ν9 intensities was clarified. In addition, line positions and intensities were obtained for two 12C2H6 hot bands (ν9+ν4?ν4, ν9+2ν4?2ν4) and the ν9 band of 13C12CH6, as well as several hundred presently unidentified transitions. N2- and self-broadened half-width coefficients were determined for over 1700 transitions, along with 1350 corresponding temperature dependence exponents. Similar to N2- and self-broadened half-width coefficients, their temperature dependence exponents were also found to follow distinctively different patterns. However, while the self- and N2-broaded widths differed by 40%, the temperature dependence exponents of the two broadening gases were similar. The variations of the observed half-width coefficients and their temperature dependences with respect to J, K quantum numbers were modeled with a set of linear equations for each K. The present broadening coefficients compared well with some of the prior measurements. 相似文献
76.
Norman C. Craig Michael C. Moore Robert L. Sams 《Journal of Molecular Spectroscopy》2006,235(2):181-189
The 2,3-13C2 isotopomer of butadiene was synthesized, and its fundamental vibrational fundamentals were assigned from a study of its infrared and Raman spectra aided with quantum chemical predictions of frequencies, intensities, and Raman depolarization ratios. For two C-type bands in the high-resolution (0.002 cm−1) infrared spectrum, the rotational structure was analyzed. These bands are for ν11 (au) at 907.17 cm−1 and for ν12 (au) at 523.37 cm−1. Ground state and upper state rotational constants were fitted to Watson-type Hamiltonians with a full quartic set of centrifugal distortion constants and two sextic ones. For the ground state, A0 = 1.3545088(7) cm−1, B0 = 0.1469404(1) cm−1, and C0 = 0.1325838(2) cm−1. The small inertial defects of butadiene and two 13C2 isotopomers, as well as for five deuterium isotopomers as previously reported, confirm the planarity of the s-trans rotamer of butadiene. 相似文献
77.
Profeta LT Sams RL Johnson TJ Williams SD 《The journal of physical chemistry. A》2011,115(35):9886-9900
Glyoxal, methylglyoxal, and 2,3-butanedione (diacetyl) are all known biomass burning effluents and suspected aerosol precursors. Pressure-broadened quantitative infrared spectra of glyoxal, methylglyoxal, and diacetyl vapors covering the 520-6500 cm(-1) range are reported at 0.112 cm(-1) resolution, each with a composite spectrum derived from a minimum of 10 different sample pressures for the compound, representing some of the first quantitative intensity data for these analytes. Many vibrational assignments for methylglyoxal are reported for the first time, as are some near-IR and far-IR bands of glyoxal and diacetyl. To complete the vibrational assignments, the far-infrared spectra (25-600 cm(-1)) of all three vapors are also reported, those of methylglyoxal for the first time. Density functional theory and ab initio MP2 theory are used to help assign vibrational modes. Potential bands for atmospheric monitoring are discussed. 相似文献
78.
A design of polarization-maintaining retro-reflectors(PMRRs) for folded-path applications is proposed and analyzed.The prism-based scheme enables the output light,which is parallel to the input,to have an identical state of polarization.The principle of the design is theoretically verified,and the related error is analyzed due to possible manufacturing imperfection.The maximum spatial angle error is ±2.75°.The effect on the extinction ratio and insertion loss is also discussed,which further proves the design’s feasibility in practical applications. 相似文献
79.
本文证明了n+k多体系(k≥4)的全部可能的封闭网均可以通过若干相应的子n+3相多体系的拼合运算得出,从而为具体构造n+k相多体系(k≥4)的全部合理的封闭网,提供了基本方法。 相似文献
80.
在文献[1]中,我们导出了超导临界温度T-c的一个严格级数表式.本文讨论这个级数的收敛范围,以及通过解析延拓来扩展收敛范围的可能性.结论是:我们的Tc级数(指文献[1]原来的级数,或者经过延拓后的级数)在∞>λ>λ0的整个范围内,都是收敛的.这里λ0是Matsubara表象中使决定Tc的方程具有正实数解的最小的λ值.它实际上就是库伦赝势.因此,也许除了少数非常弱耦合的超导体以外,我们的Tc级数能适用于一切超导体. 相似文献