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排序方式: 共有243条查询结果,搜索用时 31 毫秒
31.
Dobereiner GE Nova A Schley ND Hazari N Miller SJ Eisenstein O Crabtree RH 《Journal of the American Chemical Society》2011,133(19):7547-7562
A new homogeneous iridium catalyst gives hydrogenation of quinolines under unprecedentedly mild conditions-as low as 1 atm of H(2) and 25 °C. We report air- and moisture-stable iridium(I) NHC catalyst precursors that are active for reduction of a wide variety of quinolines having functionalities at the 2-, 6-, and 8- positions. A combined experimental and theoretical study has elucidated the mechanism of this reaction. DFT studies on a model Ir complex show that a conventional inner-sphere mechanism is disfavored relative to an unusual stepwise outer-sphere mechanism involving sequential proton and hydride transfer. All intermediates in this proposed mechanism have been isolated or spectroscopically characterized, including two new iridium(III) hydrides and a notable cationic iridium(III) dihydrogen dihydride complex. DFT calculations on full systems establish the coordination geometry of these iridium hydrides, while stoichiometric and catalytic experiments with the isolated complexes provide evidence for the mechanistic proposal. The proposed mechanism explains why the catalytic reaction is slower for unhindered substrates and why small changes in the ligand set drastically alter catalyst activity. 相似文献
32.
T.R. Canada R.A. Eisenstein C. Ellegaard P.D. Barnes J. Miller 《Nuclear Physics A》1973,205(1):145-167
The γ-decay of excited states in 210Bi up to 3330 keV excitation energy has been studied using the 209Bi(d, pγ)210Bi reaction. From the observed decay scheme, tentative Jπ values are made for 25 states. The excitation energies, (d, p) strengths and decay branching ratios of these states are compared with those calculated using the two-particle shell-model wave functions of Kim and Rasmussen and Kuo and Herling. 相似文献
33.
A. Rougé G. De Rosny P. Fleury B. Eisenstein P. Briandet P. Benkheiri P. Rivet A. Volte B. Bouquet B. DAlmagne A. Ferrer A. Jacholkowski P. Petroff F. Richard P. Roudeau J. Six D. Treille H. Yoshida 《Physics letters. [Part B]》1977,69(1):115-118
In π?p interactions at 9 GeV/c and 12 GeV/c, the forward production of N11680 and N11520 has been observed with features of nucleon exchange. The production of Δ1232 is strongly suppressed. 相似文献
34.
SCF wavefunctions with similar extended Gaussian bases for the series HCOX with X = H, OH (syn and anti), NH2, CN, and F yield closely similar charge deformation density maps in the formyl region of all six molecules. The differences, measured by moments of partitioned atomic deformation densities, correlate almost linearly with the Hammett substituent parameters σI and σR of the several substituents X. However, systematic deviations, especially in the carbon fragment, suggest the need for modified values of the inductive parameters σI for the correlation of these molecular charge densities. 相似文献
35.
36.
Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Duboscq JE Ecklund KM Ehrlich R Fields L Galik RS Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Stroiney S Sun WM Wilksen T Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N 《Physical review letters》2006,96(9):092003
We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively. 相似文献
37.
Adam NE Alexander JP Berkelman K Cassel DG Crede V Duboscq JE Ecklund KM Ehrlich R Fields L Galik RS Gibbons L Gittelman B Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Shepherd MR Stroiney S Sun WM Urner D Wilksen T Weaver KM Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C 《Physical review letters》2006,96(8):082004
We observe signals for the decays psi(3770) --> XJ/psi from data acquired with the CLEO detector operating at the CESR e+ e- collider with square root of s = 3773 MeV. We measure the following branching fractions Beta(psi(3770) --> XJ/psi and significances: (189 +/- 20 +/- 20) x 10(-5) (11.6sigma) for X = pi+ pi-, (80 +/- 25 +/- 16) x 10(-5) (3.4sigma) for X = pi0 pi0, and (87 +/- 33 +/- 22) x 10(-5) (3.5sigma) for X = eta, where the errors are statistical and systematic, respectively. The radiative return process e+ e- --> gamma psi(2S) populates the same event sample and is used to measure Gamma ee[psi(2S)] = (2.54 +/- 0.03 +/- 0.11) keV. 相似文献
38.
Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N Naik P Sedlack C Selen M White EJ Wiss J Shepherd MR Besson D Pedlar TK Cronin-Hennessy D Gao KY Gong DT Hietala J Kubota Y Klein T Lang BW Poling R Scott AW Smith A Dobbs S Metreveli Z Seth KK Tomaradze A Zweber P Ernst J Severini H Dytman SA Love W Mehrabyan S Savinov V Aquines O Li Z Lopez A Mendez H Ramirez J Xin B Huang GS Miller DH Pavlunin V Sanghi B Shipsey IP Adams GS Anderson M Cummings JP Danko I Napolitano J He Q Insler J 《Physical review letters》2006,96(8):081802
Using of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: pi+ pi- pi0 pi0, pi+ pi+ pi- pi- pi0, pi+ pi0 pi0, pi+ pi+ pi- pi0, eta pi0, and omega pi+ pi-. Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D --> pi pi rates allow us to extract the ratio of isospin amplitudes A(DeltaI = (3/2) / A(DeltaI = (1/2)) = 0.420 +/- 0.014(stat) +/- 0.016(syst) and the strong phase shift of delta1 = (86.4 +/- 2.8 +/- 3.3) degrees, which is quite large and now more precisely determined. 相似文献
39.
Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Duboscq JE Ecklund KM Ehrlich R Fields L Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Stroiney S Sun WM Wilksen T Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N Naik P 《Physical review letters》2006,96(12):121801
We present the first experimental limits on high-q2 contributions to charmless semileptonic decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias determinations of /Vub/ from inclusive measurements of B-->Xulupsilon. Using a wide range of models based on available theoretical input we set a limit of GammaWA/Gammab-->u<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of /Vub/. 相似文献
40.
M. Kellogg J.P. Eisenstein L.N. Pfeiffer K.W. West 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):6
Single-layer longitudinal and Hall resistances have been measured in a bilayer two-dimensional electron system at νT=1 with equal but oppositely directed currents flowing in the two layers. At small effective layer separation and low temperature, the bilayer system enters an interlayer coherent state expected to exhibit superfluid properties. We detect this nascent superfluidity through the vanishing of both resistances as the temperature is reduced. This corresponds to the counterflow conductivity rising rapidly as the temperature falls, reaching by . This supports the prediction that the ground state of this system is an excitonic superfluid. 相似文献