Study of tert-Amyl Methyl Ether Low Temperature Oxidation Using Synchrotron Photoionization Mass Spectrometry
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This paper examines the oxidation reaction of tert-amyl methyl ether (TAME), an oxygenated fuel additive, with chlorine radical initiators in the presence of oxygen. Data are collected at 298, 550, and 700 K. Reaction intermediates and products are probed by a multiplexed chemical kinetics synchrotron photoionization mass spectrometer (SPIMS) and characterized on the basis of the mass-to-charge ratio, ionization energy, and photoionization spectra. Branching fractions of primary products are obtained at the different reaction temperatures. CBS-QB3 computations are also carried out to study the potential energy surface of the investigated reactions to validate detected primary products.Keywords:
Branching (polymer chemistry)
Photoionization of the Ce3+ and Ce3+@C60 in the energy region 100–150 eV has been studied using our recently developed random phase approximation with exchange method and model potential for the C60 fullerene. Comparison of the results of the Ce3+ photoionization with a recent measurement (Muller et al 2008 Phys. Rev. Lett. 101 133001) confirms the value of the measured cross section for Ce3+ and indirectly supports the observed suppression effect of the carbon cage in the endohedral fullerene Ce@C+82 photoionization. Our calculation of the Ce3+@C60 photoionization process demonstrates both the suppression and the resonance effect of the C60 shell.
Endohedral fullerene
Random phase approximation
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The R-matrix method was implemented to treat molecular photoionization problem based on the UK R-matrix codes. This method was formulated to treat photoionization process long before, however, its application has been mostly limited to photoionization of atoms. Application of the method to valence photoionization as well as inner-shell photoionization process will be presented.
Photoionization mode
Matrix (chemical analysis)
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Chemists typically use photoionization and photoionization mass spectroscopy for two types of experiments. In one case, the goal is measurement of thermodynamic and spectroscopic properties. In the other case, reaction mechanisms and kinetics are probed; photoionization is used for selective identification of key species in a complex reacting mixture. The utility of photoionization stems from the ability to tie thermodynamic values to accurately measured wavelengths and the sensitivity of ion (or electron) detection.
Photoionization mode
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The number density effect in photoionization cross section of an isolated resonance has been studied using our accurate expression of photoionization cross section. The results show that it is physically reasonable to calculate the photoionization cross-sections in real system by using the suggested dielectric influence function (DIF).
Photoionization mode
Dielectric function
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We have combined B-spline basis sets with R-matrix theory for the description of photoionization in two-electron systems and applied this combination to the study of irregularities in He photoionization when doubly excited resonances up to the $N=9$ threshold of ${\mathrm{He}}^{+}$ are reached. Both total and partial photoionization cross sections have been obtained. Since the magnitude of the resonance effects is very similar for all partial cross sections, we believe that experimental investigations of photoionization cross sections leaving ${\mathrm{He}}^{+}$ in a highly excited state could provide the most information about possible long-range fluctuations in the photoionization cross sections.
Photoionization mode
R-matrix
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In this paper we study the effects of photoionization processes on the propagation of both negative and positive streamer discharges. We show that negative fronts accelerate in the presence of photoionization events. The appearance and propagation of positive streamers travelling with constant velocity is explained as the result of the combined effects of photoionization and electron diffusion. The photoionization range plays an important role for the selection of the velocity of the streamer as we show in this work.
Photoionization mode
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Photoionization mode
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In this work the roles of the shake-off and knockout processes in the double photoionization of the CH2Cl2 and CH4 molecules have been studied. The probabilities for both mechanisms accompanying valence-shell photoionization have been estimated as a function of incident photon energy using Samson's (1990) and Thomas's (1994) models, respectively. The experimental results are in qualitative accord with the models.
Photon energy
Electron shell
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Photoionization plays an important role in the mechanism of positive streamer discharges in air. The photoelectron production rate at high pressures is significantly overestimated in the widely used quantitative photoionization model in nitrogen-oxygen mixtures. A new photoionization model is proposed to surmount this disadvantage approximately by tracking the generation and deactivation of high excited states of N2. Implementation, validation, and discussion of the new photoionization model are presented in this paper. The photoionization coefficient, the fraction of nitrogen ionization events that leads to oxygen photoionization events without quenching, is computed in the new model. It decreases with the increasing pressure when E/p is constant, which agrees with the early experimental results and corrects the overestimation of the photoionization coefficients at high pressures to some extent. Simulations of positive streamers show that the generation and deactivation of high excited states of N2 weaken the discharge of nitrogen and enhance the nonlocal discharge of oxygen with a time delay in the new model. The time delay slows down the positive streamer discharges in our simulations.
Photoionization mode
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Double photoionization of atomic Na has been investigated by combining the results of photoelectron and photoion spectroscopies from synchrotron radiation measurements in the photon energy range between 50 and 135 eV. Distinction with regard to the double-photoionization mechanism (one-step or two-step processes) and to final-state configuration allowed an accurate determination of the relative cross section for one-step direct double photoionization. Above 71 eV photon energy double photoionization is dominated by 2s photoionization followed by Auger decay (two-step process) whereas direct double photoionization accounts for only \ensuremath{\simeq}20% of double photoionization.
Photoionization mode
Photon energy
Autoionization
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