Substitution reactions between gaseous ions and neutral substrate molecules are of ongoing high interest. To investigate these processes in a qualitative and quantitative manner, we have constructed a device, with which a defined amount of a volatile substrate can be mixed with a defined amount of helium gas and added into a three‐dimensional quadrupole ion trap. From the known inner volume of the device, the known ratio nsubstrate:nHe of the mixture, and the determined absolute partial pressure of helium in the ion trap, we can derive the partial pressure of the substrate in the ion trap and, thus, convert the directly observable pseudo–first‐order rate constants of the substitution reactions into absolute bimolecular rate constants. We have tested the device by investigating a series of SN2 reactions of Br ? and CF3CH2O ? anions as well as ligand exchange reactions of ligated Na+ cations. As the obtained results suggest, the described device makes it possible to determine the bimolecular rate constants of substitution reactions as well as other ion‐molecule reactions with satisfactory accuracy and reliability. 相似文献
In this communication, γ‐phenyl‐γ‐butyrodithiolactone (DTL1) is presented as the first example of a new type of control agent. The styrene polymerization carried out at 60 °C in the presence of DTL1 exhibits living characteristics, without consuming DTL1 during the process. This unprecedented behavior was explained by a mechanism based on the reversible formation of a persistent radical adduct between the DTL1 and the polystyrene macroradicals.
One of the most interesting problems of modern physics is the realization of nanoparticles in macroscopic quantum states, in which they behave as a quantum objects. These states can only be implemented at ultra-low translational temperatures that have not been achieved so far. Here we develop a novel method for optical cooling of CaF2:Yb3+ nanocrystals, which is based on the coherent population transfer induced in the impurity ions by ultraviolet Raman pulses. A doped nanocrystal localized in a radio-frequency trap is cooled due to the photon recoil from the pulses of varied intensity. The proposed method allows to obtain nanocrystals with translational temperatures of the order of 10?9 K, which indicates that the nanocrystal approaches a macroscopic quantum state. 相似文献
The accessibility of the critical parameters for the superfluid to Mott insulator quantum phase transition in a 2D permanent
magnetic lattice is investigated. We determine the hopping
matrix element J, the on-site interaction U, and hence the ratio J/U, in the harmonic oscillator wave function approximation.
We show that for a range of realistic parameters the critical values of J/U, predicted by different methods for the Bose-Hubbard
model in 2D, such as mean field theory and Monte Carlo simulations, are accessible in a 2D permanent magnetic lattice. The
calculations are performed for a 2D permanent magnetic lattice created by two crossed arrays of parallel rectangular magnets
plus a bias magnetic field. 相似文献
We discuss the zero temperature phase diagram of a dilute gas with three fermionic species. We make use of solvable limits to conjecture the behavior of the system in the “unitary” regions. The physics of the Thomas-Efimov effect plays a role in these considerations. We find a rich phase diagram with superfluid, gapless superfluid and inhomogeneous phases with different symmetry breaking patterns. We then discuss one particular possible experimental implementation in a system of 6Li atoms and the possible phases arising in this system as an external magnetic field is varied across three overlapping Feshbach resonances. We also suggest how to experimentally distinguish the different phases. 相似文献
A study of an efficient blue light‐emitting diode based on a fluorescent aryl polyfluorene (aryl‐F8) homopolymer in an inverted device architecture is presented, with ZnO and MoO3 as electron‐ and hole‐injecting electrodes, respectively. Charge‐carrier balance and color purity in these structures are achieved by incorporating poly(9,9‐dioctylfluorene‐co‐N‐(4‐butylphenyl)‐diphenylamine (TFB) into aryl‐F8. TFB is known to be a hole‐transporting material but it is found to act as a hole trap on mixing with aryl‐F8. Luminance efficiency of ≈6 cd A?1 and external quantum efficiency (EQE) of 3.1% are obtained by adding a small amount (0.5% by weight) of TFB into aryl‐F8. Study of charge injection and transport in the single‐carrier devices shows that the addition of a small fraction of hole traps is necessary for charge‐carrier balance. Optical studies using UV–vis and fluorescence spectroscopic measurements, photoluminescence quantum yield, and fluorescence decay time measurements indicate that TFB does not affect the optical properties of the aryl‐F8, which is the emitting material in these devices. Luminance efficiency of up to ≈11 cd A?1 and EQE values of 5.7% are achieved in these structures with the aid of improved out‐coupling using index‐matched hemispheres. 相似文献
The electrical properties of oxides grown on 3C-SiC by rapid thermal processing in various oxidizing and annealing atmospheres are investigated using a quasi-static method. According to the anomalous capacitance hump, the existence of two types of traps, interface and near interface oxide traps, is observed in quasi-static. By monitoring the sweep-rate measurement of the quasi-static current related to electron tunneling from interface traps to near-interface oxide traps, a profile of the traps in response time can be obtained. Based on the extracted parameters of the carrier traps, we demonstrate that the near SiO2/3C-SiC interface is significantly improved when using 100% N2O compared to 100% O2 or even N2-O2 dilution as oxidizing gas. Also, we show that incorporating N2 during the oxidation in O2 is not favourable for the reduction of the near-interface oxide traps. 相似文献
In this article we report an expression for the thermoluminescence light, which is derived from the set of differential equations by assuming negligible retrapping, but without resorting to the quasi-equilibrium approximation. The expression has been employed for analysing the glow curve of KMgF3:Lu fluoroperovskite compounds. 相似文献