The electron beam technique in carbon monoxide: Rotational transition probabilities

The electron beam fluorescence technique was developed to measure the rotational level population in the ground state of a carbon monoxide molecule. The data on rotational transition probabilities under ionization–excitation of CO (X¹Σ⁺) into the CO⁺ (B²Σ⁺) state by high energy electrons are presented, which noticeably differ from those predicted by the dipole excitation model. A flow in a free jet was used to obtain the experimental data in a low temperature rotationally equilibrium gas target. The probability matrix is represented in a compact form corresponding to the sudden approximation model.     

Total electron scattering cross-sections for carbon monoxide at low electron energies

Absolute total electron scattering cross-sections for carbon monoxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 22 electron energies varying from 0.73 to 9.14 eV with an accuracy of ±3%. The cross-sections obtained in the present experiment have been compared with other measurements and theoretical computations.     

一种在线式电子束能量测量方法

针对直线感应电子加速器中的束流特点,设计了一种在线式电子束能量测量方法。该方法使用分析磁铁和束位置探测器对电子束团切片平均能量进行测量,避免了束团取样带来的误差及测量过程对束流的影响,可以实现电子能量的在线测量。使用该方法对某强流直线感应电子加速器的电子束团能量进行了测量,获得了电子束团切片平均能量随时间变化的曲线,能量测量不确定度为0.177 MeV,能散度测量不确定度为0.39%。     

一种在线式电子束能量测量方法

针对直线感应电子加速器中的束流特点,设计了一种在线式电子束能量测量方法。该方法使用分析磁铁和束位置探测器对电子束团切片平均能量进行测量,避免了束团取样带来的误差及测量过程对束流的影响,可以实现电子能量的在线测量。使用该方法对某强流直线感应电子加速器的电子束团能量进行了测量,获得了电子束团切片平均能量随时间变化的曲线,能量测量不确定度为0.177 MeV,能散度测量不确定度为0.39%。     

A study of the electron quenching of excimers in a KrF* laser excited by a coaxial electron beam

Measurements of the output energy, the optical pulse length and the build-up time of the laser pulse, obtained with a coaxially e-beam pumped KrF^* laser, were performed varying the total gas fill pressure, the F₂ content and the e-beam current from 1–5 bar, 0.1–0.8% and 13.3–26.6 kA, respectively. The maximum specific extraction energy amounts to 64 J/l. The large range of measurements, especially at low F₂ concentrations, reveals the necessity to extend the kinetics of the F₂ chain in the usual computer model. With the introduction of electron quenching of KrF^* and ArF^* by dissociative attachment the predictions are also for low F₂ concentration in agreement with experiments.     

电子束在弯曲螺线管中的运动

为研究HIRFL-CSR电子冷却装置中电子束穿过电子冷却装置中弯曲螺线管后电子横向能量的变化,用POISSON程序计算出弯曲螺线管的磁场分布,考虑了空间电荷效应,用数值方法模拟计算了电子在弯曲螺线管中的运动情况,得到了电子束横向能量变化最小时磁场各分量与电子束能量和弯曲螺线管几何尺寸之间的关系,并获得了电子束横向能量在束流截面的空间分布。     

电子束在弯曲螺线管中的运动

 为研究HIRFL-CSR电子冷却装置中电子束穿过电子冷却装置中弯曲螺线管后电子横向能量的变化,用POISSON程序计算出弯曲螺线管的磁场分布,考虑了空间电荷效应,用数值方法模拟计算了电子在弯曲螺线管中的运动情况,得到了电子束横向能量变化最小时磁场各分量与电子束能量和弯曲螺线管几何尺寸之间的关系,并获得了电子束横向能量在束流截面的空间分布。     

An electron energy loss study of aluminum single crystals exposed to carbon monoxide

Aluminum single crystals of orientations {111}, {110}, and {100} were exposed at room temperature to carbon monoxide. The electron energy loss spectra of the exposed surfaces (> 20000 L) were essentially the same as those of clean surfaces. Since such spectra are very sensitive to small amounts of absorbate (e.g., 0.001 to 0.01 monolayer of oxygen), it is inferred that carbon monoxide does not adsorb on these clean low-order faces at room temperature. Similar results were obtained on polycrystalline and evaporated film samples. This finding contrasts with previous work on aluminum exposed to carbon monoxide.     

Multi-pulsed intense electron beam emission from velvet,carbon fibers,carbon nano-tubes and dispenser cathodes

The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources.The tested cathodes include velvet,carbon fibers,carbon nano-tubes(CNTs)and dispenser cathodes.The results indicate that all four are able to emit multi-pulsed beams.For velvet,carbon fiber and CNTs,the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse.For dispenser cathodes tested in the experiment,although there is a little difference from pulse to pulse for some reason,thermal-electric field emission may be the main process.     

Multi-pulsed intense electron beam emission from velvet, carbon fibers, carbon nano-tubes and dispenser cathodes

The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources. The tested cathodes include velvet, carbon fibers, carbon nano-tubes (CNTs) and dispenser cathodes. The results indicate that all four are able to emit multi-pulsed beams. For velvet, carbon fiber and CNTs, the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse. For dispenser cathodes tested in the experiment, although there is a little difference from pulse to pulse for some reason, thermal-electric field emission may be the main process.     

Coadsorption of oxygen and carbon monoxide on tungsten: Desorption spectra,electron stimulated desorption and field emission microscopy

CO/W desorption spectra are characterized by an α state and multiple β states; using electron stimulated desorption (ESD) the α state was shown to comprise two sub-states, α₁ and α₂. In this paper the consecutive interactions of O₂ and CO on W are investigated using ESD, flash desorption and field emission microscopy (FEM).Desorption spectra show that the α-CO state is displaced by O₂, in two stages. The ESD probe provides an identification of the first stage with the removal of the α₁-CO state, and energy analysis of ESD ions reveals a large energy shift (～ ? 1.5 eV) during O₂ coadsorption which can be attributed to an incresae in the α₁-CO WC bond length of ～ 0.15 Å. During this O₂-induced displacement, the two β peaks converge into a single peak at the β₁ position; this is ascribed to adatom interactions in the mixed O and C adlayer. Isotope exchange experiments with ²⁸CO and ³⁶O₂ reveal (i) no exchange in the α-CO states, and (ii) complete exchange in the β-CO states, which is consistent with dissociative adsorption in the latter. The amount of coadsorbed O₂ is estimated from these results, and from FEM data: a full monolayer of O adatoms can be coadsorbed on CO-saturated W, but CO pre-adsorption inhibits the formation of W oxides. The β₁-O₂ (ESD active) state also forms on the CO-covered surface: this state is identical in population, ESD cross section and ion energy distribution to β₁-O₂ on clean W, and retains its identity in the mixed layer (it does not undergo isotopic exchange). CO₂ desorption spectra from the mixed layer were also characterised, complete isotopic scrambling being observed.Pre-exposure of tungsten to O₂ inhibits CO adsorption: a monolayer of O₂ is sufficient to prevent CO adsorption, and at low O₂ coverages, every O₂ molecule preadsorbed prevents one CO molecule from adsorbing. Isotopic exchange is again complete in the β states, and a lateral interaction model for desorption kinetics, based on dissociative adsorption in the β-CO state, quantitatively describes the CO desorption spectra.     

Infrared spectra of carbon monoxide on evaporated nickel films: A low temperature thermal detection technique

A novel thermal detection scheme has been developed and combined with the techniques of rapid scan Fourier transform infrared spectroscopy to make sensitive, high resolution measurements of the vibrational spectrum of carbon monoxide molecules on evaporated nickel films. Adsorbed molecules are detected by attaching a germanium resistance thermometer to the sample, cooling the assembly to liquid helium temperatures, and measuring the temperature changes which occur when infrared radiation is absorbed. Spectra are presented for a range of CO coverages on an evaporated nickel film and a film damaged by ion bombardment. The positions, shapes, and intensities of the spectral lines from linear and bridge bonded CO molecules give information about the surface structure of the metal films and about the different ordered phases of the adsorbed molecules.     

The adsorption of oxygen and carbon monoxide on cleaved polar and nonpolar ZnO surfaces studied by electron energy loss spectroscopy

Electron energy loss spectroscopy (ELS) with primary energies e₀ ? 80 eV has been performed on ultrahigh vacuum (UHV) cleaved nonpolar (11?00) and polar zinc (0001) and oxygen (0001?) surfaces of ZnO to study the adsorption of oxygen and carbon monoxide. Except for CO on the nonpolar surface where no spectral changes in ELS are observed a surface transition near 11.5 eV is strongly affected at 300 K on all surfaces by CO and O₂. At 300 K clear evidence for new adsorbate characteristic transitions is found for oxygen adsorbed on the Zn polar surface near 7 and 11 eV. At 100 K on all three surfaces both CO and O₂ adsorb in thick layers and produce loss spectra very similar to the gas phase, thus indicating a physisorbed state.     

Density functional theory investigation of carbon monoxide adsorption on the kaolinite(001) surface

Carbon monoxide(CO) is a gaseous pollutant with adverse effects on human health and the environment. Kaolinite is a natural mineral resource that can be used for different applications, including that it can also be used for retention of pollutant gases. The adsorption behavior of carbon monoxide molecules on the(001) surface of kaolinite was studied systematically by using density-functional theory and supercell models for a range coverage from 0.11 to 1.0 monolayers(ML). The CO adsorbed on the three-fold hollow, two-fold bridge, and one-fold top sites of the kaolinite(001) was tilted with respect to the surface. The strongest adsorbed site of carbon monoxide on the kaolinite(001) surface is the hollow site followed by the bridge and top site. The adsorption energy of CO decreased when increasing the coverage, thus indicating the lower stability of surface adsorption due to the repulsion of neighboring CO molecules. In addition to the adsorption structures and energetics, the lattice relaxation, the electronic density of states, and the different charge distribution have been investigated for different surface coverages.     

The relation between static disorder and photoluminescence quenching law in glasses: A numerical technique

Photoluminescence (PL) quenching, which usually obeys empirical Street law for glassy solids, is analyzed taking into account the fact that the quenching of each particular emission center is statistically described by the known Mott law. A numerical technique for retrieving energy distributions of luminescent centers from PL quenching measurements is proposed. Mathematical treatment procedure is established and tested for reliability. Calculation results for chalcogenide, quartz and lead-silicate glasses demonstrate the possibility for obtaining both ordinary and polymodal energy distributions of centers and also a good promise for application in PL spectroscopy of disordered solids.