41,841 research outputs found
Intra- and Intermolecular C−H Activation by Bis(phenolate)pyridineiridium(III) Complexes
A bis(phenolate)pyridine pincer ligand (henceforth abbreviated as ONO) has been employed to support a variety of iridium complexes in oxidation states I, III, and IV. Complexes (ONO)IrL_2Me (L = PPh_3, PEt_3) react with I_2 to cleave the Ir–C bond and liberate MeI, apparently via a mechanism beginning with electron transfer to generate an intermediate Ir(IV) complex, which can be isolated and characterized for the case L = PEt_3. The PPh_3 complex is transformed in benzene at 65 °C to the corresponding phenyl complex, with loss of methane, and subsequently to a species resulting from metalation of a PPh_3 ligand. Labeling and kinetics studies indicate that PPh_3 is the initial site of C–H activation, even though the first observed product is that resulting from intermolecular benzene activation. C–H activation of acetonitrile has also been observed
gauge vector field on a codimension-2 brane
In this paper, we obtain a gauge invariant effective action for a bulk
massless gauge vector field on a brane with codimension two by using a
general Kaluza-Klein (KK) decomposition for the field. It suggests that there
exist two types of scalar KK modes to keep the gauge invariance of the action
for the massive vector KK modes. Both the vector and scalar KK modes can be
massive. The masses of the vector KK modes contain two parts,
and , due to the existence of the two extra
dimensions. The masses of the two types of scalar KK modes and
are related to the vector ones, i.e.,
and . Moreover, we
derive two Schr\"{o}dinger-like equations for the vector KK modes, for which
the effective potentials are just the functions of the warp factor.Comment: 15 pages,no figures, accepted by JHE
Null geodesics and gravitational lensing in a nonsingular spacetime
In this paper, the null geodesics and gravitational lensing in a nonsingular
spacetime are investigated. According to the nature of the null geodesics, the
spacetime is divided into several cases. In the weak deflection limit, we find
the influence of the nonsingularity parameter on the positions and
magnifications of the images is negligible. In the strong deflection limit, the
coefficients and observables for the gravitational lensing in a nonsingular
black hole background and a weakly nonsingular spacetime are obtained.
Comparing these results, we find that, in a weakly nonsingular spacetime, the
relativistic images have smaller angular position and relative magnification,
but larger angular separation than that of a nonsingular black hole. These
results might offer a way to probe the spacetime nonsingularity parameter and
put a bound on it by the astronomical instruments in the near future.Comment: 15 pages, 5 figures, 1 tabl
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