Experimental study on synchrotron radiation photoionization of secondary organic aerosol derived from styrene ozonolysis

Secondary organic aerosol (SOA) produced by ozonolysis of styrene and other alkene compounds is a major part of fine particles in urban atmospheres. The atmospheric ozonolysis process of styrene is simulated in a smog chamber, and the formed SOA particles are detected on-line by a synchronous radiation vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in this study. Through molecular ion peaks in the photonionization mass spectra of SOA and the corresponding photoionization efficiency curve, combined with off-line measurement verification of ultraviolet visible and infrared absorption spectra, it is determined that formaldehyde, formic acid, benzene, phenol, benzaldehyde, and benzoic acid are the main constituents of styrene SOA. These provide new information for studying the atmospheric ozonolysis oxidation mechanism of styrene. VUV-PIMS can get over complicated sample preparation procedures, secondary pollution, and other shortcomings of the off-line method and is a useful instrument to measure constituents and unveil the formation process of SOA particles.     

Vacuum ultraviolet photoionization mass spectrometric study of cyclohexene

In this work, photoionization and dissociation of cyclohexene have been studied by means of coupling a reflectron time‐of‐flight mass spectrometer with the tunable vacuum ultraviolet (VUV) synchrotron radiation. The adiabatic ionization energy of cyclohexene as well as the appearance energies of its fragment ions C₆H₉⁺, C₆H₇⁺, C₅H₇⁺, C₅H₅⁺, C₄H₆⁺, C₄H₅⁺, C₃H₅⁺ and C₃H₃⁺ were derived from the onset of the photoionization efficiency (PIE) curves. The optimized structures for the transition states and intermediates on the ground state potential energy surfaces related to photodissociation of cyclohexene were characterized at the ωB97X‐D/6‐31+g(d,p) level. The coupled cluster method, CCSD(T)/cc‐pVTZ, was employed to calculate the corresponding energies with the zero‐point energy corrections by the ωB97X‐D/6‐31+g(d,p) approach. Combining experimental and theoretical results, possible formation pathways of the fragment ions were proposed and discussed in detail. The retro‐Cope rearrangement was found to play a crucial role in the formation of C₄H₆⁺, C₄H₅⁺ and C₃H₅⁺. Intramolecular hydrogen migrations were observed as dominant processes in most of the fragmentation pathways of cyclohexene. The present research provides a clear picture of the photoionization and dissociation processes of cyclohexene in the 8‐ to 15.5‐eV photon energy region. Copyright © 2016 John Wiley & Sons, Ltd.     

Dissociative photoionization of Al2(Ch3)6 and Al2(Ch3)3Cl3 in the range 40–100 eV

Dissociation processes of the organoaluminum compounds Al₂(CH₃)₆ and Al₂(CH₃)₃Cl₃ have been studied in the range of valence and Al:2p core-level ionization by means of photoelectron–photoion and photoion–photoion coincidence techniques. The double-ionization threshold and the Al:2p core-ionization threshold of Al₂(CH₃)₆ are estimated to be about 30 and 80 eV

1 1 eV = 96.4853 kJ mol^?1.

respectively. The relative yields of the H⁺?Al⁺ and H⁺?CH_m,⁺ (m′ = 0–3) ion pairs are enhanced around the Al:2p core-ionization threshold of Al₂(CH₃)₆. The photoion–photoion coincidence intensities of Al₂(CH₃)₃Cl₃ are negligibly small throughout the energy range studied. The ratio of the relative yield of AlC₂H₆⁺ to that of Al⁺ increases smoothly through the Al:2p core-ionization and/or excitation region of Al₂(CH₃)₃Cl₃. The variation of the fragmentation pattern with photon energy is discussed in conjunction with the relevant electronic states.     

Investigation on the absolute and relative photoionization cross sections of 3 potential propargylic fuels

Absolute photoionization cross sections for 2 potential propargylic fuels (propargylamine and dipropargyl ether) along with the partial ionization cross sections for their dissociative fragments are measured and presented for the first time via synchrotron photoionization mass spectrometry. The experimental setup consists of a multiplexed orthogonal time‐of‐flight mass spectrometer and is located at the Advanced Light Source facility of the Lawrence Berkeley National Laboratory in Berkeley, California. Data for a third propargylic compound (propargyl alcohol) were taken; however, because of its low signal, due to its weakly bound cation, only the dissociative ionization fragment from the H‐loss channel is observed and presented. Suggested pathways leading to formation of dissociative photoionization fragments along with CBS‐QB3 calculated adiabatic ionization energies and appearance energies for the dissociative fragments are also presented.     

Dissociative photoionization of isoprene: experiments and calculations

Vacuum ultraviolet (VUV) dissociative photoionization of isoprene in the energy region 8.5–18 eV was investigated with photoionization mass spectroscopy (PIMS) using synchrotron radiation (SR). The ionization energy (IE) of isoprene as well as the appearance energies (AEs) of its fragment ions C₅H₇⁺, C₅H₅⁺, C₄H₅⁺, C₃H₆⁺, C₃H₅⁺, C₃H₄⁺, C₃H₃⁺ and C₂H₃⁺ were determined with photoionization efficiency (PIE) curves. The dissociation energies of some possible dissociation channels to produce those fragment ions were also determined experimentally. The total energies of C₅H₈ and its main fragments were calculated using the Gaussian 03 program and the Gaussian‐2 method. The IE of C₅H₈, the AEs for its fragment ions, and the dissociation energies to produce them were predicted using the high‐accuracy energy model. According to our results, the experimental dissociation energies were in reasonable agreement with the calculated values of the proposed photodissociation channels of C₅H₈. Copyright © 2009 John Wiley & Sons, Ltd.     

Absolute photoionization cross sections of two cyclic ketones: cyclopentanone and cyclohexanone

Absolute photoionization cross sections for cyclopentanone and cyclohexanone, as well as partial ionization cross sections for the dissociative ionized fragments, are presented in this investigation. Experiments are performed via a multiplexed photoionization mass spectrometer utilizing vacuum ultraviolet (VUV) synchrotron radiation supplied by the Advanced Light Source of Lawrence Berkeley National Laboratory. These results allow the quantification of these species that is relevant to investigate the kinetics and combustion reactions of potential biofuels. The CBS‐QB3 calculated values for the adiabatic ionization energies agree well with the experimental values, and the identification of possible dissociative fragments is discussed for both systems. Copyright © 2017 John Wiley & Sons, Ltd.     

New results on the dissociative photoionization of CF(4) and CCl(4)

Using the VIPCO technique, we remeasured and completed the breakdown diagram of CCl(4) (+) up to 21 eV energy. The angle-resolved data show both orientation and alignment of photoelectrons relative to CX(3) (+) fragments from photoionization to the low-lying states of CF(4) (+) and CCl(4) (+). The strength of the orientation (forward/backward asymmetry) is surprising in view of the nearly spherical symmetry of the parent molecules, and calls for theoretical explanation. It may indicate that nuclear and electron motion take place on similar time-scales.     

偶氮苯的同步辐射光电离及光解离

芳香族偶氮化合物(通式为Ar-N=N-Ar)是品种最多、应用最广的一类合成染料。由于偶氮苯类化合物容易发生感光异构[1],近年来已引起材料学家对它们的光子模式信息存储性能方面的广泛关注[2,3]。本文报道同步辐射光电离质谱法研究偶氮苯获得了该类物质的IP、AP、D0等重要参数。1　实验采用光束线编号为U10A同步辐射光源[4],工作波段35-300nm,分辨λ/△λ>500,波长精度±0 1nm,样品处光通量在1011光子/秒,样品处光斑大小3(水平)×1(垂直)mm。实验样品为固体,所以在光电离室电离区的正下方安装了一个加热炉,将固态样品放在炉内,通过调节…     

In search of new resonance structures in dissociative photoionization of H2

We present a theoretical study of dissociative photoionization of H₂ via the ¹Π_u symmetry in the photon energy range 30–43 eV. Our results explain the various peaks observed in the experiments below 40 eV and illustrate, in particular, the important role of the ²Π_u(2pπ_u) ionization threshold. At higher photon energies, they suggest the existence of new resonance structures that may be associated with doubly excited states of H₂ lying above the third and fourth ionization thresholds (the Q₃ and Q₄ resonance series). From the calculated resonance parameters, we conclude that the dominant mechanism at high photon energies should involve the Q₄ (and probably higher) doubly excited states of H₂. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

CH3I同步辐射光电离及生成焓、键能和质子亲合势的测定

在超声射流冷却条件下用VUV同步辐射研究了CH3I分子的光电离过程。测定了CH3I光电离及解离电离产生的CH3I^+, CH3^+和I^+的出现势, 结合已确认的热力学数据, 估算出体系中有关离子的标准生成焓、分子和分子离子的键能、自由基的质子亲合势及母体离子的解离能等数据。对CH3I分子VUV光解离电离通道进行了分析。     

对当量为1的预混乙烯/氧气/氩气火焰的实验研究

A comprehensive experimental study of the premixed ethylene/oxygen/argon flame at 2.667 kPa with a stoichiometric equivalence ratio (φ=1) was performed with the tunable synchrotron photoionization and molecular-beam sampling mass spectrometry techniques. The isomers of most observed species in the flame were unambiguously identified by measurements of the photoionization efficiency spectra, e.g. C3H4, C2H4O and C4H4. The mole fraction profiles of species up to C7H8 were measured by scanning the burner position at the selected photon energies near ionization thresholds, and the flame temperature profile was obtained by using Pt/Pt-13%Rh thermocouple. Compared with the previous studies, a lot of new flame species:C3H2, C3H3, C3H5, C2H6O, C4H2, C4H4, C4H6, C3H4O, C3H6O, C3H8O, C5H6, C4H8O and C7H8, were observed. A series of free radicals in the flame are detected to be CH3, C2H3, C2H5, HCO, C3H3 and C3H5.Based on the experimental work, a reduced reaction mechanism was developed including 40 species and 223 reactions. Modeling and measurements agree well for the major species and most intermediates. A detailed kinetic model is desired for this flame.     

Kr和Kr2的实验和理论研究

利用超声分子束技术、同步辐射和反射式飞行时间质谱仪得到了Kr和Kr2的光电离质谱和光电离效率谱, 确定了Kr和Kr2的电离能. 利用Gaussian-03程序中的MP2(Full)/6-31G*, QCISD/cc-pVTZ以及B3LYP/6-31G方法优化了Kr2的结构, 计算了它们的振动频率和电离能, 计算结果显示: 当采用相同的理论水平和基组时, 随着Kr同位素质荷比(m/z)的增大, 它们结构和电离能保持不变, 而振动频率逐渐变小. 与此同时, 用G2方法计算了Kr (84)和Kr2 (168)的电离能, 它们的电离能的理论值与实验结果符合得比较好.     

Dynamic behavior of highly excited molecular states in the strong monochromatic laser fields

The dynamic behavior of highly excited molecular states in an external monochromatic field has been investigated in order to establish the general trends in the Rydberg state manifestations in collisional and radiative processes. The effects of interference between direct (background) and resonant interactions and coupling between the continua on the fine structure of collision cross sections and near-threshold photoabsorption spectra are discussed. Analytical expressions for the widths and intensities of the Rydberg lines induced by mixing the field with other quasistationary states are derived and their dependence on the external field strength and frequency are analyzed. It was found that the appreciable stabilization of isolated Rydberg levels observed previously in superstrong fields is also possible in fields much weaker than atomic fields. The possibility of laser control for the energy averaged cross sections and reaction rate constants are considered. All effects are illustrated for thee ^– + H₂ ⁺ system.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 367–386, March, 1994.This work was supported by the Russian Foundation for Basic ReSearch (Grant No. 93-03-4700).     

Hole Migration in Telomere-Based Oligonucleotide Anions and G-Quadruplexes

Vacuum ultraviolet photoionization of a gas-phase oligonucleotide anion leads to the formation of a valence hole. This hole migrates towards an energetically favorable site where it can weaken bonds and ultimately lead to bond cleavage. We have studied Vacuum UV photoionization of deprotonated oligonucleotides containing the human telomere sequence dTTAGGG and G-quadruplex structures consisting of four dTGGGGT single strands, stabilized by NH₄⁺ counter ions. The oligonucleotide and G-quadruplex anions were confined in a radiofrequency ion trap, interfaced with a synchrotron beamline and the photofragmentation was studied using time-of-flight mass spectrometry. Oligonucleotide 12-mers containing the 5'-TTAGGG sequence were found to predominantly break in the GGG region, whereas no selective bond cleavage region was observed for the reversed 5'-GGGATT sequence. For G-quadruplex structures, fragmentation was quenched and mostly non-dissociative single and double electron removal was observed.     

Photoionization and dissociation of the monoterpene limonene: mass spectrometric and computational investigation

The photoionization of the monoterpene limonene has been studied using tunable vacuum ultraviolet synchrotron radiation in the region from the threshold for ionization of the parent molecule up to 15.5 eV. The adiabatic ionization energy of limonene is derived from photoionization efficiency spectrum and found to be 8.27 eV, compared with the density functional theory calculations which yields a value of 8.08 eV (B3LYP/6-311++G). Primary dissociation pathways of the parent molecule ions are investigated by experimental observations and theoretical calculations. Most of the fragmentation channels occur via a rearrangement reaction prior to dissociation. Transition structures and intermediates for those isomerization processes are also determined.     

基于同步辐射光电离质谱的燃烧与能源研究新方法

化石燃料为当今世界提供了超过80％的能源,其大量消耗所引起的能源危机和环境问题已成为全球关注的热点问题．解决此问题的关键在于深入理解燃烧和能源转化过程中的化学反应机理,进而从本质上探寻提高燃烧效率与减少污染物排放的方法．本文回顾了本课题组近年来发展的多种基于同步辐射光电离质谱技术的新方法和新装置,及其在燃烧与能源研究中的应用,并对未来可以发展的新方法和新方向进行了展望．     

Experimental and theoretical investigation of the photoionization of hydrogen cyanide

Cryogenic matrices containing molecular aggregates of methyl nitrite or methanol have been irradiated with a cw CO₂ laser. At the irradiation frequency hole burning was observed by means of a grating infrared spectrophotometer. The results suggest that vibrational absorption lineshapes of aggregates in cryogenic matrices are dominated by inhomogeneous line-broadening.     

Higher-order processes in X-ray photoionization of atoms

There are several fourth-generation X-ray light source projects now underway around the world and it is anticipated that by the end of the decade, one or more of these X-ray free-electron lasers will be operational. In this contribution, we describe recent measurements and future plans to study both multielectron and multiphoton atomic photoionization. Although such higher-order processes are rare with present third-generation sources, they will be commonplace in experimental work with the new sources. The topics we discuss here are double K-shell ionization and two-photon X-ray photoionization.     

Radiation grafting of styrene onto poly(vinylidene fluoride) films in propanol: The influence of solvent and synthesis conditions

Electron‐beam‐irradiated poly(vinylidene fluoride) films were grafted with styrene with propanol or toluene as a solvent. The influence of the synthesis conditions and, more particularly, of the solvent was investigated. In propanol, the order of dependence of the grafting rate is 0.43 on the pre‐irradiation dose and 1.2 on the monomer concentration. The activation energy of the grafting reaction in propanol is approximately 73 kJ/mol. Both the initial grafting rate and the saturation degree of grafting are considerably higher in propanol, which is unable to swell polystyrene grafts, than in toluene, which diffuses with styrene through the grafted moiety. The grafting solvent also influences the structure of the membrane: films grafted in propanol have a much reduced elongation at break and a rougher surface. It is suggested that phase‐separated polystyrene domains may be larger when grafting is carried out in a styrene–propanol solution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1512–1519, 2000     

VUV photodissociation of thiazole molecule investigated by TOF‐MS and photoelectron photoion coincidence spectroscopy

Photoelectron photoion coincidence measurements have been performed for the thiazole (C₃H₃NS) molecule in gas phase, using time‐of‐flight mass spectrometry in the electron‐ion coincidence mode and vacuum ultraviolet synchrotron radiation. photoelectron photoion coincidence spectra have been recorded as a function of the photon energy covering the valence range from 10 to 21 eV. The resulting photoionization products as well as the dissociation pathways leading to the ionic species were proposed and discussed. We have also performed density functional theory and ab initio calculations for the neutral molecule, its cation and the ion fragments produced in order to determine their electronic and structural parameters. Copyright © 2014 John Wiley & Sons, Ltd.