Analytical Laser Photoionization Spectroscopy of Calcium and Sodium on a General-Purpose Laser Photoionization Spectrometer

We have designed a new combination analytical laser spectrometer that operates simultaneously in the atomic beam mode and in the flame mode. We demonstrate the analytical capabilities of the spectrometer, using as an example determination of the sodium and calcium content in standard solutions and aluminum alloys. For these elements, efficient excitation schemes through Rydberg states are realized. The calcium and sodium contents in aluminum alloys were determined at the 10^–2% and 10^–3% level respectively.     

Photoionization of atoms and ions

Calculations of subshell photoionization processes are performed for various atoms (neon, argon, iron and uranium), for various degrees of ionization, within the independent-particle approximation. We discuss the asymptotic behavior and the high-energy features of these cross sections, focusing on subshell cross-section ratio functions. Near threshold, a modified Dirac-Fock theory is used to study core relaxation effects on photoabsorption for argon. Finally we examine the ionic neon total photoabsorption cross section as a function of degree of ionization.     

Photoionization coefficient of thin calcium films

The photoionization coefficient of thin calcium films was studied by means of photoemission measurements. The incident photon energies ranged from 2 eV to 5.6 eV. The films were obtained by thermal evaporation and condensation on a silica substrate in ultrahigh vacuum. The mass thicknesses ranged from 2 nm to 50 nm. The photoionization coefficient β exhibited two maxima and reached a constant value for films thicker than 15 nm. The first maximum corresponds to a granular structure (d₁ = 3 nm; β₁ = 62 × 10^?31 per absorbed quantum in a second). The second maximum corresponds to the granular-lacunar structure transition (d₀ ≈ 5.5 nm; β₀ = 36 × 10^?31 per absorbed quantum in a second). An attempt is made to explain the result in terms of an electronic double layer located near the surface.     

小型光电离反射式飞行时间质谱计

介绍了合肥国家同步辐射实验室光化学站自行研制的小型光电离反射式飞行时间质谱计。该仪器以YAG激光器或同步辐射光作为激发光源，不仅可以开展气相分子的光电离、解离研究，而且可以开展固相样品激光溅射的离子团簇的研究。它具有智能化程度高、结构紧凑和质量分辨率高等优点。     

Photoionization pathways and free electrons in UV-MALDI

The recently developed model for primary and secondary UV-MALDI ion formation (Knochenmuss, R. J. Mass Spectrom. 2002, 37, 867-877. Knochenmuss, R. Anal. Chem. 2003, 75, 2199.) is applied to questions regarding photoionization pathways and electron versus negative ion production. Two-photon ionization of the matrix in direct contact with analyte is possible under some circumstances (Kinsel, G.; Knochenmuss, R.; Setz, P.; Land, C. M.; Goh, S.-K.; Archibong, E. F.; Hardesty, J. H.; Marynik, D. J. Mass Spectrom. 2002, 37, 1131-1140.), and is added to the model. When analyte is present in large mole ratios (such as when matrix suppression is desired), this effect contributes modestly to the ion yield. Generally, matrix exciton pooling remains dominant. The interfacial layer of thin samples on a metal substrate may also be ionizable in a 2-photon process. A mechanism is proposed, and the correspondingly modified model gives excellent agreement with electron emission versus laser intensity data. Capture in, or escape of low-energy electrons from a thick sample (or on a nonmetallic substrate) is also examined. Because the mean free path for MALDI electrons in a solid matrix is on the order of 10 nm, below such depths, any electrons generated are captured to form negative ions. Only a surface layer can emit free electrons. This surface emission effect is also well reproduced by the model, up to a laser intensity limit caused by surface charging. This charging phenomenon is investigated and illustrated by molecular dynamics calculations.     

Laser Photoionization Spectroscopy of Single Atoms and Molecules

A new, highly sensitive method of laser spectroscopy of atoms and molecules based on multiple photon ionization is described. The history, characteristics and some key applications of this method are presented.     

Photoionization studies of atoms and molecules using synchrotron radiation

Photoionization studies of free atoms and molecules have undergone considerable development in the past decade, in large part due to the use of synchrotron radiation. The tunability of synchrotron radiation has permitted the study of photoionization processes near valence- and core-level ionization thresholds for atoms and molecules throughout the Periodic Table. A general illustration of these types of study will be presented, with emphasis on a few of the more promising new directions in atomic and molecular physics being pursued with synchrotron radiation.     

Photoionization cross sections: Present status and future needs

The existing experimental data situation for photoionization cross sections of ground-state atoms, excited states and positive ions is reviewed. The ability of theory to predict these cross sections is also discussed. The likely progress for the near future is presented.     

Fragment-Free Mass Spectrometric Analysis with Jet Cooling/VUV Photoionization

We show that it is possible to obtain fragment-free mass spectra of large molecules by a combination of laser desorption, jet cooling, and VUV single-photon photoionization. The ability to obtain parent molecular masses is particularly important for the analysis of mixtures, such as combinations of fully saturated hydrocarbons. By varying the cooling conditions, we can also achieve partial fragmentation in order to obtain further structural information. The use of different wavelengths provides additional selectivity between aromatic and aliphatic compounds.     

空气源热泵回收空调系统排风能量的节能利用探讨

文章对目前空调系统排风中能量回收利用过程中存在的不足进行了理论分析和相关的技术数据比较,提出了基于空气源热泵空调排风的深度节能利用方案,即把空调系统排风引入到空气源热泵室外换热器,利用空调系统的排风具有的能量来加强空气源热泵室外换热器的换热强度,从而提高空气源热泵的制冷、制热系数和机组的制冷(热)量,减少电能消耗。该方案在技术上可行,初投资小、回收年限短、能量回收率高(可以达到100%)、节能效果显著。     

Differences between alveolar air and mouth air

Our breath contains an intraoral and an alveolar part, the latter being the last to be exhaled. As such, major differences in composition can be expected, with for alveolar air the inclusion of more metabolic compounds released during the blood-air exchange. This study explored the differences between breath air from the oropharynx and from the lungs in healthy volunteers. Mouth and alveolar air of 40 volunteers was analyzed using gas chromatography-mass spectrometry, together with a sample of room air. A chromatogram of a single person contains on average 145 different compounds. Altogether, 618 compounds were detected. A total of 35 compounds were common to all volunteers. The number of compounds was significantly higher in mouth air than in alveolar air. For 47 compounds, very significant differences in detection/concentration were recorded. Gas chromatography-mass spectrometry offers a detailed overview of the compounds in a person's breath. One should be aware of the distinction between alveolar air and oropharyngeal air.     

空分设备空气预冷系统技术改造

利用环氧乙烷装置产生的高温冷凝水作为空分设备空气预冷系统冷水机组的驱动热源,来获得低温冷冻水,代替原来的冷水机组去冷却空气,既降低了原有冷水机组的电耗,又解决了高温水的排放污染问题。介绍空气预冷系统改造后流程以及为保持工况稳定而增设的冷却水回水温度联锁功能,分析技术改造所取得的效益。     

利用空压机气源复热空分设备的操作实践

介绍了利用压缩空气复热空分设备的具体操作要点、操作步骤 ,并与常规自然复热的方法进行对比 ,说明采用新工艺取得较好的经济效益。     

全液体空分设备仪表气系统的改造

KDON-6000Y/4000Y型全液体空分设备大量采用气动调节阀,所以仪表气源的稳定可靠对整套空分设备的安全运行起着举足轻重的作用。在现有设备的基础上增设一台空浴式汽化器,改善了空分设备原仪表气系统,提高了系统安全系数。简析原仪表气系统存在的问题和整改方案,介绍整改后仪表气系统的操作要点和效果。     

室内空气品质与新风量控制

鉴于室内污染物的主要来源及其交叉感染，介绍室内空气品质的评价指标与改善措施，分析新风系统的分配问题，探讨新风量控制的方法与改进。     

容克式空预器漏风故障分析及处理

容克式空气预热器是大中型电站锅炉上广泛采用的尾部换热设备,漏风率高是该类设备常见故障。本文对漏风原因进行分析,提出密封间隙调整和加强吹灰治理等对策,从而有效降低空预器漏风率。     

气流组织对空气品质的影响分析

气流组织对空气品质起着非常重要的影响，在相同风量的情况下，选择不同的气流组织形式，可获得不同的空气品质。     

Investigation of Laser Selective Photoionization of 177mLu Isomer to Create a 177mLu/177Lu Generator

Radiochemistry - The selectivity and efficiency of laser photoionization of the 177mLu nuclear isomer by a three-stage photoionization scheme of lutetium 5d6s2...     

Photoionization effect in liquid xenon doped with triethylamine (TEA) or trimethylamine (TMA)

Photoionization effects have been observed in liquid xenon doped with triethylamine (TEA) or trimethylamine (TMA) by using a small multiwire chamber whose anode consists of 9 wires of 10 μm in diameter. Quantum efficiencies for photoionization in both dopants are estimated to be close to unity for photons emitted from liquid xenon. Electron multiplication related to proportional scintillation was observed at wire voltages above about 3 kV. The energy resolution in ionization mode for alpha particles is improved from 15% to 4% (fwhm) by introducing TEA.