Novel synthesis of enamines by iridium-catalyzed dehydrogenation of tertiary amines

A novel route to enamines is reported, the dehydrogenation of tertiary amines catalyzed by a "pincer-ligated" iridium catalyst.     

SF6 ground-based infrared solar absorption measurements: long-term trend, pollution events, and a search for SF5CF3 absorption

Infrared solar spectra recorded with the Fourier transform spectrometer in the McMath solar telescope complex on Kitt Peak (31.9°N latitude, 111.6°W, altitude), southwest of Tucson, Arizona, have been analyzed to retrieve average SF₆ tropospheric mixing ratios over a two-decade time span. The analysis is based primarily on spectral fits to absorption by the intense, unresolved ν₃ band Q branch at . A best fit to measurements recorded with SF₆ near typical background concentrations yields a SF₆ increase in the average tropospheric mixing ratio from (10⁻¹² per unit volume) in March 1982 to in March 2002. The long-term increase by a factor of 3.34 over the time span is consistent with the rapid growth of surface mixing ratios measured in situ at Northern Hemisphere remote stations, though the infrared measurements show a large scatter. Average tropospheric mixing ratio enhancements above background by 2-3 orders of magnitude have been identified in spectra recorded on 5 days between November 1988 and April 1997. These spectra were individually analyzed in an attempt to detect the strongest 8- band of SF₅CF₃, a molecule recently identified with an atmospheric growth that has closely paralleled the rise in SF₆ during the past three decades. Absorption by the strongest SF₅CF₃ band was predicted to be above the noise level in the Kitt Peak spectrum with the highest average mean tropospheric SF₆ mixing ratio, assuming the reported atmospheric SF₅CF₃/SF₆ ratio and a room temperature absorption cross sections reported for the SF₅CF₃ 903-cm⁻¹ band. An upper limit of 8×10¹⁵ for the SF₅CF₃ total column was estimated for this case. We hypothesize that the highly elevated SF₆ levels above Kitt Peak resulted from a local release experiment rather than production via electrochemical fluoridation of intermediate products, the proposed source of atmospheric SF₅CF₃. The absence of the SF₅CF₃ feature in the spectra with elevated SF₆ is consistent with the absence of SF₅CF₃ reported in a pure SF₆ sample.     

Mechanism of alkane transfer-dehydrogenation catalyzed by a pincer-ligated iridium complex

The mechanism of (PCP)Ir-catalyzed transfer-dehydrogenation has been elucidated for the prototypical substrate/acceptor couple, COA/TBE, at 55 degrees C (COA = cyclooctane; TBE = tert-butylethylene). The catalytic cycle may be viewed as the sum of two reactions: (i) hydrogenation of TBE by (PCP)IrH2 and C-H addition of a second mole of TBE to give (PCP)IrH(tert-butylvinyl), and (ii) dehydrogenation of COA by (PCP)IrH(tert-butylvinyl) to give (PCP)IrH2, COE, and TBE. These two stoichiometric reactions have been observed independently and their kinetics determined. The overall catalysis has also been monitored in situ, and (PCP)IrH2 and (PCP)IrH(tert-butylvinyl) have been observed as the resting states; the ratio of these two complexes is found to be proportional to [TBE]2. Based upon the proportionality constant thus obtained and the catalytic rate as a function of [TBE] (which reaches a maximum at ca. 0.3 M), the respective rate constants for the hydrogenation and dehydrogenation segments can be obtained. Good agreement is found between the rates independently obtained from stoichiometric and catalytic runs. Within the overall TBE-hydrogenation reaction, labeling experiments indicate that the rate-determining step is the reductive elimination of TBA (2,2-dimethylbutane) from (PCP)IrH(tert-butylethyl) (which is formed via insertion of TBE into an Ir-H bond of (PCP)IrH2). Based upon considerations of microscopic reversibility, it can be further inferred that the rate-determining step for the alkane dehydrogenations is C-H addition (and not beta-H elimination).     

Search for the lepton family number violating process nu(mu)e(-) --> mu(-)nu(e)

The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to perform a search for the lepton number violating process nu(mu)e(-)-->mu(-)nu(e), and to measure the cross section of the standard model inverse muon decay process nu(mu)e(-)-->mu(-)nu(e). NuTeV measures the inverse muon decay asymptotic cross-section slope sigma/E to be (13.8 +/- 1.2 +/- 1.4) x 10(-42) cm(2)/GeV. The experiment also observes no evidence for lepton number violation and places one of the most restrictive limits on the cross-section ratio sigma(nu(mu)e(-)-->mu(-)nu(e))/sigma(nu(mu)e(-)-->mu(-)nu(e)) < or = 1.7% at 90% C.L. for V-A couplings and < or = 0.6% for scalar couplings.     

平面电磁波的表示及偏振旋转方向的判定

在给出平面波偏振旋转方向定义的基础上写出电磁波的几种表示方式，并以其中某些量的性质来判断波的偏振旋转方向。在物理教学中也可体现出这种定义的优越性。     

激光雷达观测的武汉上空中层顶附近重力波活动及谱分布

利用钠共振荧光激光雷达于 1 996年3月 1～ 3日在武汉对中层顶 ( 75～ 1 0 5km)高度的钠原子层进行了探测 .通过分析探测数据得到了该区域的相对大气密度起伏及垂直波数谱分布 .平均大气密度起伏均方根值为 5 % ,平均谱斜率为 - 2 .2 3.     

Infrared spectral radiance of hot HF and DF in the Δv = 1 bands region as seen through an atmospheric path

Individual spectral line parameters of the Δv = 1 HF bands at elevated temperatures have been generated. Line by line, layer by layer, spectral radiance and absorptance calculations have been compared with previous experimental results. The HF lines and a recent compilation of infrared atmospheric spectral line parameters have been used to compute the infrared spectral radiance from a hot HF source and a given atmospheric path on a line by line, layer by layer basis.     

Electron cooling of high-Z ion beams parallel to a guidemagnetic field

The cooling of high-Z ion beams through collisions with electrons whose temperature parallel to a guide magnetic field is considerably lower than their perpendicular temperature is considered. For initial electron temperatures, magnetic fields, and charged-particle densities, electrons tend to be trapped in the vicinity of their nearest ion neighbor. This results in an energy exchange with the ions that is qualitatively different from conventional models, where electron cooling is described in terms of small angle collisions or within the linearized dielectric response theory. Such models are justified for situations where the potential energy of interactions is small compared to the relevant kinetic energy; e.g. for light ions. For the case of high-Z ions, however, it is the trapping process itself that drives the cooling. Using a variety of parameterizations of the electron shielding of the ions, it is found that resulting steady-state ion temperature parallel to the magnetic field is less than a factor of ten higher than the original parallel electron temperature. The e-folding times of approach to the equilibrium temperature have been found to be on the order of a few milliseconds for Z in the range of 20 and above. This result is encouraging with respect to the production of ultracold beams or even a crystalline heavy-ion state     

Vibrational Raman scattering temperature measurements

Experimental data and analyses are presented for the determination of gas temperature by measurements of vibrational Raman scattering intensity ratios of Stokes Q-branch fundamental bands. The method is demonstrated for two thermal equilibrium experiments: (1) CO₂ (a gas well-suited for use in multi-component mixtures near ambient temperatures) in a test cell, and (2) N₂ (a gas well-suited for use at elevated temperatures) in a flame. This method of temperature measurement is of particular value for non-thermal equilibrium conditions, for which vibrational excitation temperatures can be assigned to each pair of vibrational level corresponding to observable Raman bands.