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排序方式: 共有225条查询结果,搜索用时 15 毫秒
191.
Li S Schmidt JR Piryatinski A Lawrence CP Skinner JL 《The journal of physical chemistry. B》2006,110(38):18933-18938
Vibrational spectral diffusion denotes the time-dependent fluctuations of a solute's vibrational frequencies due to local environmental dynamics. Vibrational line shapes are weakly sensitive to spectral diffusion, whereas three-pulse vibrational echoes are much more sensitive. We report here on theoretical studies of spectral diffusion of the asymmetric stretch of the azide anion in heavy water. We run a classical molecular dynamics simulation of rigid azide in rigid water, and at every time step we calculate the azide's anharmonic asymmetric stretch frequency using an optimized quantum mechanics/molecular mechanics method developed earlier. This generates a frequency trajectory, which we use to calculate the absorption line shape and integrated three-pulse echo intensity. Our results for both the line width and the integrated echo intensity are in excellent agreement with experiment. Our calculated frequency time-correlation function is in excellent agreement with experiment for long times (greater than 250 fs) but differs considerably from experiment at short times; our theoretical correlation function has a very pronounced oscillation, presumably due to intermolecular azide-water hydrogen-bond stretching dynamics. 相似文献
192.
Joseph A. Connor Nabila I. El-Saied Jose A. Martinho-Simoes Henry A. Skinner 《Journal of organometallic chemistry》1981,212(3):405-410
Microcalorimetric measurements at 520–523 K of the heats of thermal decomposition and of iodination of bis-(benzene)molybdenum and of bis-(toluene)tungsten have led to the values (kJ mol?): ΔHof[Mo(η-C6H6)2, c] = (235.3 ± 8) and ΔHof[W(η6-C7H8)2, c] = (242.2 ± 8) for the standard enthalpies of formation at 25°C. The corresponding ΔHof(g) values, using available and estimated enthalpies of sublimation, are (329.9 ± 11) and 352.2 ± 11) respectively, from which the metalligand mean bond-dissociation enthalpies, (Mo—benzene) = (247.0 ± 6) and (W—toluene) = (304.0 ± 6) kJ mol?1, are derived. 相似文献
193.
van den Brink HB Blok HP Bobeldijk I Bouwhuis M Dodge GE Harakeh MN Hesselink WH Ireland DG de Jager CW Jans E de Jonge N Kalantar-Nayestanaki N Kasdorp WJ Ketel TJ Konijn J Lapikás L van Leeuwe JJ van der Meer RL Nooren GJ Norum BE Passchier E Pellegrino AR Spaltro CM van der Steenhoven G Steijger JJ Templon JA Theunissen JA van Uden MA de Vries H de Vries R de Witt Huberts PK 《Physical review letters》1995,74(18):3561-3564
194.
We suggest an architecture for quantum computing with spin-pair encoded qubits in silicon. Electron-nuclear spin-pairs are controlled by a dc magnetic field and electrode-switched on and off hyperfine interaction. This digital processing is insensitive to tuning errors and easy to model. Electron shuttling between donors enables multiqubit logic. These hydrogenic spin qubits are transferable to nuclear spin-pairs, which have long coherence times, and electron spin-pairs, which are ideally suited for measurement and initialization. The architecture is scalable to a highly parallel operation. 相似文献
195.
Erik M. Muller John Smedley Jen Bohon Xi Yang Mengjia Gaowei John Skinner Gianluigi De Geronimo Michael Sullivan Marc Allaire Jeffrey W. Keister Lonny Berman Annie Héroux 《Journal of synchrotron radiation》2012,19(3):381-387
Two transmission‐mode diamond X‐ray beam position monitors installed at National Synchrotron Light Source (NSLS) beamline X25 are described. Each diamond beam position monitor is constructed around two horizontally tiled electronic‐grade (p.p.b. nitrogen impurity) single‐crystal (001) CVD synthetic diamonds. The position, angle and flux of the white X‐ray beam can be monitored in real time with a position resolution of 500 nm in the horizontal direction and 100 nm in the vertical direction for a 3 mm × 1 mm beam. The first diamond beam position monitor has been in operation in the white beam for more than one year without any observable degradation in performance. The installation of a second, more compact, diamond beam position monitor followed about six months later, adding the ability to measure the angular trajectory of the photon beam. 相似文献
196.
M.Robin Bendall Thomas E. Skinner 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,134(2):331-349
To provide the most efficient conditions for spin decoupling with least RF power, master calibration curves are provided for the maximum centerband amplitude, and the minimum amplitude for the largest cycling sideband, resulting from STUD+ adiabatic decoupling applied during a single free induction decay. The principal curve is defined as a function of the four most critical experimental input parameters: the maximum amplitude of the RF field,RFmax, the length of the sech/tanh pulse,Tp, the extent of the frequency sweep,bwdth,and the coupling constant,Jo. Less critical parameters, the effective (or actual) decoupled bandwidth,bweff, and the sech/tanh truncation factor, β, which become more important asbwdthis decreased, are calibrated in separate curves. The relative importance of nine additional factors in determining optimal decoupling performance in a single transient are considered. Specific parameters for efficient adiabatic decoupling can be determined via a set of four equations which will be most useful for13C decoupling, covering the range of one-bond13C1H coupling constants from 125 to 225 Hz, and decoupled bandwidths of 7 to 100 kHz, with a bandwidth of 100 kHz being the requirement for a 2 GHz spectrometer. The four equations are derived from a recent vector model of adiabatic decoupling, and experiment, supported by computer simulations. The vector model predicts an inverse linear relation between the centerband and maximum sideband amplitudes, and it predicts a simple parabolic relationship between maximum sideband amplitude and the productJoTp. The ratiobwdth/(RFmax)2can be viewed as a characteristic time scale, τc, affecting sideband levels, with τc≈Tpgiving the most efficient STUD+ decoupling, as suggested by the adiabatic condition. Functional relationships betweenbwdthand less critical parameters,bweffand β, for efficient decoupling can be derived from Bloch-equation calculations of the inversion profile for a single sech/tanh pulse. Residual splitting of the centerband, normally associated with incomplete or inefficient decoupling, is not seen in sech/tanh decoupling and therefore cannot be used as a measure of adiabatic decoupling efficiency. The calibrated experimental performance levels achieved in this study are within 20% of theoretical performance levels derived previously for ideal sech/tanh decoupling at high power, indicating a small scope for further improvement at practical RF power levels. The optimization procedures employed here will be generally applicable to any good combination of adiabatic inversion pulse and phase cycle. 相似文献
197.
A study of the thermal decomposition of an acetylene–ethane-d6 mixture indicates that the rate constant for hydrogen abstraction from acetylene by methyl is more than 20 times less than for abstraction from ethane. Isotopic exchange is initiated by a rapid reaction between product D atoms and C2H2. A series of experiments involving the reactions of a D2–acetylene mixture indicated that a molecular exchange process was also occurring, and it was shown that d[C2HD]/dt = k[D2]0.7[C2H2]0.3, effective activation energy = 15.8 kcal/mol. This mechanism made an insignificant contribution to isotope exchange in C2H2–C2D6 mixtures. 相似文献
198.
I. M. Skinner 《Optical and Quantum Electronics》1986,18(5):345-354
A simple method to obtain accurate explicit approximation formulae for the properties of an elliptical dielectric waveguide is explained. As examples, expressions for the propagation constant, geometric birefringence, and generalized two-dimensional Petermann spot-size are derived for step refractive index profiles. 相似文献
199.
200.