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Rapid and sensitive detection of formaldehyde using portable 2-dimensional gas chromatography equipped with photoionization detectors
摘要： We developed an automated and highly portable device for rapid and sensitive formaldehyde detection based on heart-cutting 2-dimensional gas chromatography. In this design, the air sample was first absorbed by a preconcentrator before it is injected into the 1st-dimensional column (Rtx?-VMS). The partial elution from the 1st-dimensional column containing formaldehyde was re-injected into the 2nd-dimensional column (Rt? Q-BOND column) for further separation. The detection of formaldehyde was achieved by using a micro-helium dielectric barrier discharge photoionization detector that is able to ionize formaldehyde (ionization potential = 10.88 eV). Due to the use of many miniaturized components, the entire system has a weight of only 1.3 kg (excluding the helium cartridge) and dimensions of only 27 cm x 24 cm x 12 cm. It is capable of detecting formaldehyde down to 0.5 ppb (V/V) with a signal-to-noise ratio of 6 in only 11 min (including 6 min of sampling). Meanwhile, simultaneous separation and detection of other air pollution related toxic compounds, such as benzene, toluene, ethylbenzene, and xylene, was also demonstrated by the 1-dimensional column and a flow-through micro-photoionization detector. The device developed here should have a broad range of applications in environmental protection, industries, space exploration, and battlefield.
关键词： Gas chromatography,Air quality control,Indoor air analysis,Photoionization detector,2D GC,Formaldehyde detection
更新于2025-09-23 15:23:52
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The Effect of Environmental Temperature on Negative Corona Discharge Under the Action of Photoionization
摘要： The properties of corona discharge in practical applications are strongly influenced by the variation of environmental parameters. A 2-D axisymmetric hydrodynamic drift–diffusion model coupled with Poisson’s equation and three Helmholtz differential equations is established to investigate the effect of environmental temperature on negative corona discharge under the action of photoionization. This numerical model is performed by a traditional needle-to-plane configuration in dry air at atmospheric pressure. The characteristics of Trichel pulses, negative ion density, electric field, and electron density are discussed in this paper. It is found that the magnitude of Trichel pulses, first pulse duration, and pulse frequency increase with increasing the ambient temperature. Moreover, the effect of photoionization under these conditions is also investigated by simulations intensively.
关键词： negative corona discharge,Trichel pulses,Environmental temperature,photoionization
更新于2025-09-23 15:22:29
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A Study of the Kinetic Parameters of Lu Laser Photoionization Scheme
摘要： Development of the laser photoionization method for obtaining 177Lu radionuclide for a medical purpose requires the knowledge of the light-saturation intensities at each stage of the Lu photoionization scheme (5d6s2 2D3/2?5d6s6p 4F5/2?5d6s7s 4D3/2?(53375 cm–1)), taking into account the used components of the hyperfine structure of transitions. The effective excitation cross sections of various hyperfine transition components for 175Lu, 176Lu, 177Lu, and 177mLu isotopes have been experimentally determined for radiations of pulsed tunable dye lasers pumped by copper-vapor lasers.
关键词： laser isotope separation,177Lu,hyperfine structure,laser photoionization
更新于2025-09-23 15:21:01
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In-source laser photoionization spectroscopy of Bi isotopes: accuracy of the technique and methods of data analysis
摘要： The in-source laser photoionization spectroscopy was applied to study neutron-deficient Bi isotopes. Data analysis and accuracy-related aspects of this technique are discussed. The accuracy of the peak position evaluation is estimated. An “integration method” for nuclear spin determination in the case of partially resolved hyperfine spectra is discussed in detail.
关键词： Nuclear charge radii,In-source laser photoionization spectroscopy,Nuclear electromagnetic moments
更新于2025-09-23 15:21:01
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states of Rb in simultaneous magneto-optical trapping of Rb and Hg
摘要： We report the measurement of the photoionization cross sections of the 5S1/2 and 5P3/2 states of 87Rb in a two-species Hg and Rb magneto-optical trap (MOT) by the cooling laser for Hg. The photoionization cross sections of Rb in the 5S1/2 and 5P3/2 states at 253.7 nm are determined to be 1+4.3 × 10?20 cm2 and 4.63(30) × 10?18 cm2, respectively. To measure the 5S1/2 and 5P3/2 state fractions in the MOT we detected the photoionization rate of the 5P3/2 state by an additional 401.5 nm laser. The photoionization cross section of Rb in the 5P3/2 state at 401.5 nm is determined to be 1.18(10) × 10?17 cm2.
关键词： Hg,laser cooling,Rb,magneto-optical trap,photoionization cross sections
更新于2025-09-23 15:21:01
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X-ray emission from layered media irradiated by an x-ray free-electron laser
摘要： This article presents a computational study of the x-ray ?uorescence induced by the irradiation of thin layered media by intense, short x-ray pulses. The treatment is based on a numerical solution of the Helmholtz wave equation both for the pump and for the ?uorescence signal. Consistently with a possible heating of the medium during the x-ray pulse, complex refractive indices are calculated at each time step from the results of an underlying treatment of atomic physics. In the context of an important core-hole production as a result of photoionization, we discuss the peculiarities of the resulting ampli?ed ?uorescence grazing emission and of the Bragg diffraction which can be realized at some angles inside a multilayer material or even in a perfect crystal.
关键词： multilayer material,x-ray fluorescence,Bragg diffraction,complex refractive indices,photoionization,perfect crystal,Helmholtz wave equation
更新于2025-09-23 15:19:57
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Selection of the magnetic quantum number in resonant ionization of neon using an XUV-IR two-color laser field
摘要： A recent experiment [Villeneuve et al. Science 356, 1150 (2017)] has shown that two-color photoionization of neon by the combination of an attosecond XUV pulse train and a moderately strong, linearly polarized IR pulse can preferentially produce photoelectrons with orbital angular quantum number l = 3 (f-wave) and magnetic quantum number m = 0. This result was rationalized by the occurrence of different Stark shifts of m = 0 and |m| = 1 sub-levels in the IR laser field. Here we perform 3D time-dependent Schrodinger equation calculations with a neon effective potential to identify the mechanism for the selective excitation and ionization of m = 0 sub-levels. Calculations of the ionization and excitation yields as a function of the IR intensity and the XUV and IR photon energy reveal that a coupling between two dominant ionization channels involving 3p and 3d intermediate excitations is responsible for the observed m-level selectivity. We compare calculated and measured photoelectron velocity map images and ionization yields over a range of IR intensities and XUV and IR photon energies, and confirm that the m = 0 or |m| = 1 channel, and thus a single set of the quantum numbers, (Jion, l, m), can be selected by an appropriate choice of these parameters.
关键词： photoelectron velocity map images,XUV-IR laser field,neon,time-dependent Schrodinger equation,two-color photoionization,magnetic quantum number,Stark shifts
更新于2025-09-23 15:19:57
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Tuning photoionization mechanisms of molecular hybrid materials for EUV lithography applications
摘要： The investigation of the photoionization processes of a series of titanium oxo clusters evidenced that doping their organic shell with extended aromatic structures decreases their ionization energy and stabilises the resulting radical cations. Such tunability of their photochemistry arising from ligand exchange gives these hybrid compounds great potential as EUV photoresists.
关键词： photoionization,titanium oxo clusters,EUV lithography,ligand exchange,photoresists
更新于2025-09-23 15:19:57
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Is methanol a dopant under atmospheric pressure photoionization conditions?
摘要： Using a modified atmospheric pressure photoionization (APPI) source coupled to a tunable vacuum ultraviolet source at the SOLEIL synchrotron radiation facility, we determined the appearance energy of protonated methanol monomer and dimers at different source temperatures. The experimental data indicated that protonated monomers can be formed through the direct photoionization of neutral methanol by the second emission band of a krypton discharge UV lamp at 116.49 nm (10.64 eV) explaining why methanol can be considered as a weak dopant under APPI conditions. This point is in contradiction with the previously proposed mechanism where photoionization of methanol dimer was followed by the dissociation of the protonated methanol dimer into protonated methanol monomer.
关键词： dopant,synchrotron,ionization process,methanol,Atmospheric pressure photoionization
更新于2025-09-19 17:15:36
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Measurement of photoionization cross-section of Li (2p, 3d) excited states using thermionic diode detector
摘要： Studies on photoionization cross-section measurement of lithium 2p and 3d excited states selectively populated by single and two photons are reported. The photoionization is carried out in a heat-pipe cum thermionic diode detector using nitrogen laser pumped pulsed dye laser. Rhodamine perchlorate (Rh-640) dye is used to generate the desired tunable laser output in the range of 635 to 675 nm. Both, the thermionic diode detector and dye laser are developed in-house. A negative space charge region formed around diode cathode filament is illuminated by dye laser exciting pulse followed by ionizing UV radiation from nitrogen laser. The effect of ionizing laser pulse energy and precise tuning of dye laser on photoionization signal, across 670.780 nm (2S1/2 → 2P1/2,3/2) single-photon transition and 639.145 nm (2S1/2 → 2D3/2,5/2) two-photon transition are studied. The results obtained are compared with model calculations of photoionization signal saturation curve. The ionization cross-section for both the states (2P1/2, 2D5/2) are determined as 15.40 ± 2.8 Mb and 8.04 ± 1.6 Mb, respectively and atomic number density N ～ 5.6 × 10^8 (cm^?3).
关键词： Dye laser,Photoionization cross-section,Thermionic diode,Heat-pipe,Lithium
更新于2025-09-19 17:15:36