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。     

DNA及鸟嘌呤衍生物在碱性溶液中被248nm激光单光子电离

利用纳秒级激光先解动态吸收光谱装置，研究鸟嘌呤衍生物及ＤＮＡ在碱性溶液中的光电离。首次发现鸟嘌呤衍生物及ＤＮＡ在碱性溶液中能被２４８ｕｍ激光单光子电离，确证了光电离发生在Ｎ１位脱质子的鸟嘌呤部分，测定了水合电子的量子产额。     

The photoionization of excited hydrogen atom in plasmas

The photoionization processes of excited hydrogen atoms in plasma environments are investigated using the method of complex coordinate rotation. The standard Debye–Hückel model and modified Debye–Hückel model are adopted to describe the plasma screening effects. The photoionization cross sections of plasma-embedded excited hydrogen atoms varied with different screening lengths are displayed to illustrate the influence of plasma screening. The results of the Debye–Hückel model compared with the modified Debye–Hückel are presented. The shape resonances and Cooper minima due to the plasma screening are observed and discussed.     

Analysis and Manipulation of the Structure of Odor Plumes from a Piezo-Electric Release System and Measurements of Upwind Flight of Male Almond Moths, <Emphasis Type="Italic">Cadra cautella</Emphasis>, to Pheromone Plumes

We investigated the plume structure of a piezo-electric sprayer system, set up to release ethanol in a wind tunnel, using a fast response mini-photoionizaton detector. We recorded the plume structure of four different piezo-sprayer configurations: the sprayer alone; with a 1.6-mm steel mesh shield; with a 3.2-mm steel mesh shield; and with a 5 cm circular upwind baffle. We measured a 12 × 12-mm core at the center of the plume, and both a horizontal and vertical cross-section of the plume, all at 100-, 200-, and 400-mm downwind of the odor source. Significant differences in plume structure were found among all configurations in terms of conditional relative mean concentration, intermittency, ratio of peak concentration to conditional mean concentration, and cross-sectional area of the plume. We then measured the flight responses of the almond moth, Cadra cautella, to odor plumes generated with the sprayer alone, and with the upwind baffle piezo-sprayer configuration, releasing a 13:1 ratio of (9Z,12E)-tetradecadienyl acetate and (Z)-9-tetradecenyl acetate diluted in ethanol at release rates of 1, 10, 100, and 1,000 pg/min. For each configuration, differences in pheromone release rate resulted in significant differences in the proportions of moths performing oriented flight and landing behaviors. Additionally, there were apparent differences in the moths’ behaviors between the two sprayer configurations, although this requires confirmation with further experiments. This study provides evidence that both pheromone concentration and plume structure affect moth orientation behavior and demonstrates that care is needed when setting up experiments that use a piezo-electric release system to ensure the optimal conditions for behavioral observations.     

Quantum efficiency measurement of CsI photocathodes using synchrotron radiation at BSRF

A quantum efficiency(QE) measurement system has been established for CsI photocathodes in the wavelength range of 120-210 nm by using the synchrotron radiation light source at Beijing Synchrotron Radiation Laboratory (BSRF). An AXUV100G photodiode calibrated by Physikalisch-Technische Bundesanstalt (PTB) was used as the transfer detector standard to ensure the accuracy and reliability of the QE measurement. The dependencies of QE measurement on beam energy, vacuum pressure and bias voltage were studied in detail. The influence of photoionization in gas on the QE measurement was observed and is described. The surface morphological characteristics of both substrate and CsI film were analyzed by atomic force microscopy (AFM). The QE results of differently prepared CsI photocathodes were compared, including: the printed circuit board (PCB) of FR-4 (Woven glass and epoxy)+Cu, FR-4+Cu/Ni/Au, and stainless steel substrates; a series of thickness from 60 to 600 nm; and the resistive and electron beam evaporation techniques.     

An experimental and modeling study of methyl propanoate pyrolysis at low pressure

Methyl propanoate (MP) pyrolysis in a laminar flow reactor was studied at low pressure (30 Torr) within the temperature range from 1000 to 1500 K. About 30 products were detected and identified in the pyrolysis process using the photoionization mass spectrometry, including H₂, CO, CO₂, CH₃OH, CH₂O, CH₂CO, C1 to C4 hydrocarbons and radicals (such as CH₃, C₂H₅ and C₃H₃). Their mole fraction profiles versus temperature were also measured. For the unimolecular dissociation reactions, the rate constants were calculated by high precision theoretical calculations. Based on the theoretical calculations and measured mole fraction profiles of pyrolysis species, a kinetic model of MP pyrolysis containing 98 species and 493 reactions was developed. The model simulates the primary decomposition process well with the calculated rate constants. According to the rate of production analysis, the decomposition pathways of MP and the formation channels of both oxygenated and hydrocarbon products were discussed. It is concluded that the main decomposition pathway is MP → CH₂COOCH₃ → CH₃CO + CH₂O → CO.     

Luminescence thermal quenching of M_2SiO_4:Eu~(2+)(M=Sr,Ba) phosphors

In this paper,luminescence thermal quenching of M_2SiO_4:Eu~(2+)(M=Sr,Ba) orthosilicate phosphors and mechanisms for thermal quenching proposed by different authors are briefly reviewed.Depending on preparation conditions and/or Eu~(2+)-doping concentrations,the quenching temperature(T_(1/2)) and activation energy for thermal quenching of the same orthosilicate phosphor reported by different authors are inconsistent.The common conclusion is that T_(1/2) of the intermediate compound(Ba_(1-x)Sr_x)_2 SiO_4:Eu~(2+)(x≈0.5) is higher than that of either Sr_2So_4;Eu~(2+)or Ba_2SiO_4;Eu~(2+)end-member.Moreover,T_(1/2) of the best-performing SrBaSiO_4:Eu~(2+)is evidently lower than that of YAG:Ce~(3+)and some Eu~(2+)-doped nitride phosphors.Rega rding the quenching mechanism,most of the investigators attributed thermal quenching to a thermally assisted 4f-5d cross-over in the configuration coordinate diagram.Only a few authors ascribed thermal quenching to a thermally assisted photoionization of 5 d electron to conduction band of the host.Nonetheless,a close inspection of T_(1/2) and Stokes shift derived from the vibrational spectra of the intermediate compound and end-member phosphors indicates that the 5d electron photo ionization model instead of the 4f-5d crossing decay model should be the genuine mechanism for the thermal quenching of M_2 SiO_4:Eu~(2+)(M=Sr,Ba) phosphors.Since the relationship between T_(1/2) and Stokes shift of the phosphors does not support the 4 f-5 d crossing decay model.The ionization probability of the 5 d electron depends on the energy gap(E_(dC)) between 5 d_1 level of the Eu~(2+)and conduction band minimum(CBM) of the host at higher temperatures.Lattice thermal expansion would result in an elevating 5 d_1 level of the Eu~(2+)along with a diminishing CBM of the host and as a consequence a reduction in E_(dC) and an enhanced photo ionization probability at elevated temperatures.A less rigid lattice and hence a larger coefficient of thermal expansion of M_2SiO_4 hosts should be the physical origin of poorer thermal quenching properties of the orthosilicate phosphors.     

光离子化技术发展综述

回顾光离子化技术的发展历程，介绍了光离子化技术的优缺点、光离子化检测器的基本工作原理和结构，着重分析了电离室内部的电离微观机制。并以国产仪器GC-4400型便携式光离子化气相色谱仪为主，介绍了国内外近期PID技术的若干最新发展。     

Applications of the relativistic equation of motion to photoionization of Mg-like ions

As an approximation to the relativistic equation of motion, the multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization of the Mg-like ions. Photoionization cross sections between ²(2p⁶3s)S1/2 and ionization thresholds are calculated. The main feature of our results is exhibited by five Rydberg series of doubly excited states arising from fine-structure splittings. A comparative study of Al⁺, Si²⁺, P³⁺, S⁴⁺, Cl⁵⁺, and Ar⁶⁺ is presented.     

Material removal at atomic and close-to-atomic scale by high-energy photon:a case study using atomistic-continuum method

Extreme ultraviolet (EUV) light plays an important role in various fields such as material characterization and semiconductor manufacturing. It is also a potential approach in material fabrication at atomic and close-to-atomic scales. However, the material removal mechanism has not yet been fully understood. This paper studies the interaction of a femtosecond EUV pulse with monocrystalline silicon using molecular dynamics (MD) coupled with a two-temperature model (TTM). The photoionization mechanism, an important process occurring at a short wavelength, is introduced to the simulation and the results are compared with those of the traditional model. Dynamical processes including photoionization, atom desorption, and laser-induced shockwave are discussed under various fluencies, and the possibility of single atomic layer removal is explored. Results show that photoionization and the corresponding bond breakage are the main reasons of atom desorption. The method developed can be further employed to investigate the interaction between high-energy photons and the material at moderate fluence.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00374-x