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Organic peroxy radicals (RO[sub.2]) as key intermediates in tropospheric chemistry exert a controlling influence on the cycling of atmospheric reactive radicals and the production of secondary pollutants, such as ozone and secondary organic aerosols (SOA). Herein, we present a comprehensive study of the self-reaction of ethyl peroxy radicals (C[sub.2]H[sub.5]O[sub.2]) by using advanced vacuum ultraviolet (VUV) photoionization mass spectrometry in combination with theoretical calculations. A VUV discharge lamp in Hefei and synchrotron radiation at the Swiss Light Source (SLS) are employed as the photoionization light sources, combined with a microwave discharge fast flow reactor in Hefei and a laser photolysis reactor at the SLS. The dimeric product, C[sub.2]H[sub.5]OOC[sub.2]H[sub.5], as well as other products, CH[sub.3]CHO, C[sub.2]H[sub.5]OH and C[sub.2]H[sub.5]O, formed from the self-reaction of C[sub.2]H[sub.5]O[sub.2] are clearly observed in the photoionization mass spectra. Two kinds of kinetic experiments have been performed in Hefei by either changing the reaction time or the initial concentration of C[sub.2]H[sub.5]O[sub.2] radicals to confirm the origins of the products and to validate the reaction mechanisms. Based on the fitting of the kinetic data with the theoretically calculated results and the peak area ratios in the photoionization mass spectra, a branching ratio of 10 ± 5% for the pathway leading to the dimeric product C[sub.2]H[sub.5]OOC[sub.2]H[sub.5] is measured. In addition, the adiabatic ionization energy (AIE) of C[sub.2]H[sub.5]OOC[sub.2]H[sub.5] is determined at 8.75 ± 0.05 eV in the photoionization spectrum with the aid of Franck-Condon calculations and its structure is revealed here for the first time. The potential energy surface of the C[sub.2]H[sub.5]O[sub.2] self-reaction has also been theoretically calculated with a high-level of theory to understand the reaction processes in detail. This study provides a new insight into the direct measurement of the elusive dimeric product ROOR and demonstrates its non-negligible branching ratio in the self-reaction of small RO[sub.2] radicals.

Photoionization of neutral potassium K I is investigated in the framework of the screening constant per unit nu-clear charge (SCUNC) method. Transition energies and wavelengths belonging to 4p([sup.2][P.sub.1/2] [right arrow] nd [sup.2][D.sub.3/2] and 4p([sup.2][P.sub.3/2]) [right arrow] nd [D.sub.3/2,5/2] Rydberg transitions are reported. Accurate transition energies and wavelengths originating from 4p([sup.2][P.sub.1/2,3/2]) levels of KI are tabulated for 20 [less than or equal to] n [less than or equal to] 100. The SCUNC wavelengths are believed to be the first calculations that agree excellently with the existing experimental measurements up to n = 70 using linearly polarized laser light. The maximum shift in wavelengths relative to the experimental data is at 0.03 nm up to n = 70. New wavelengths are tabulated for n = 71-100 along with new transition energies for n = 20-100.

The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics 1 – 7 . Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization 8 – 12 . Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700 as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger–Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization. Time-resolved measurements of the X-ray photoemission delay of core-level electrons using attosecond soft X-ray pulses from a free-electron laser can be used to determine the complex correlated dynamics of photoionization.

State-of-the-art attosecond photoionization experiments are identified as a new platform to test Born's rule -- a postulate of quantum mechanics. A simulation of the so-called Sorkin test under typical experimental conditions infers an achievable measurement precision in the range of the best Sorkin tests to date, demonstrating new opportunities for high-precision tests of Born's rule via nonlinear matter-wave interferometry. The potential of attosecond photoionization for further fundamental tests of quantum mechanics is discussed.

In this study we investigate the dissociative photoionization of molecular hydrogen H2, addressing the influence of autoionizing states and nuclear motion on the photoelectron dynamics. Experimental results are compared with ab initio calculations.

Inhibiting the recombination of electron-hole pairs of TiO.sub.2-based photocatalysts to enhance the photocatalytic activities received continuous attention in the past decades. Herein, a ternary composite of TiO.sub.2/UiO-66-NH.sub.2/graphene oxide was designed to facilitate the photoelectrons transfer. When -NH.sub.2 was grafted, graphene oxide was introduced by 0.05 g and Ti/Zr molar ratio of the composite was 19, the composite exhibited enhanced photocatalytic performance in a period of 45 min dye removing tests (degrading rate over 97%) and a significant improvement (H.sub.2 evolution rate 0.27 mmol/h in 2 h) in hydrogen evolution tests. Furthermore, in the reversibility test, the composite could maintain high dye degrading efficiency (over 88%) after five cycles and the apparent quantum efficiency reach 8.04% in 12-h H.sub.2 evolution test which means electron-holes recombination was efficiently inhibited and the structure of the composite was relatively stable.

It is highly desired to enhance charge separation and O[sub.2] adsorption of the pyropheophorbide-a (Ppa) to promote visible-light activity and stability. Herein, Ppa modified 001-facet-exposed TiO[sub.2] nanosheets (Ppa/001T) nanocomposites with different weight ratios were fabricated via the self-assembly approach by OH induced. Compared with the bare Ppa, the 8% amount optimized 8Ppa/001T sample displayed 41-fold enhanced activity for degradation of Ametryn (AME) under visible-light irradiation. The promoted photoactivities could be attributed to the accelerated charge carrier’s separation by coupling TiO[sub.2] as thermodynamic platform for accepting the photoelectrons with high energy from Ppa and the promoted O[sub.2] adsorption because of the residual fluoride on TiO[sub.2]. As for this, a distinctive two radicals (•O[sub.2] [sup.−] and •OH) involved pathway of AME degradation is carried out, which is different from the radical pathway dominated by •O[sub.2] [sup.−] for the bare Ppa. This work is of utmost importance since it gives us detailed information regarding the charge carrier’s separation and the impact of the radical pathway that will pave a new approach toward the design of high activity visible-light driven photocatalysts.

Single and double photoionization cross-sections in the photon region straddling the nitrogen K-edge and up to photon energies of ∼450 eV, for the atomic N+ and molecular NH+ and \\({{\\rm{NH}}}_{2}^{+}\\) species were measured at the SOLEIL radiation facility in Orsay, France. The measurements are compared with theoretical estimates.

Attosecond-scale electron localization The primary event in photoexcitation — involved in processes such as photosynthesis and photoisomerization — is an electronic response that occurs on attosecond (1 as = 10 −18 s) timescales, a realm recently made accessible to spectroscopic investigation by the development of attosecond-scale light pulses. Sansone et al . report an experimental study in which electron localization in molecules is measured on attosecond timescales using pump–probe spectroscopy. H 2 and D 2 are dissociatively ionized by the sequence of an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends on the delay between the pump and probe pulses. This work demonstrates that combined experimental and computational efforts enable the use of attosecond pulses for the exploration of electron localization. Attosecond (10 −18 s) laser pulses make it possible to peer into the inner workings of atoms and molecules on the electronic timescale — phenomena in solids have already been investigated in this way. Here, an attosecond pump–probe experiment is reported that investigates the ionization and dissociation of hydrogen molecules, illustrating that attosecond techniques can also help explore the prompt charge redistribution and charge localization that accompany photoexcitation processes in molecular systems. For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10 −15 -s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale 1 , 2 , 3 , 4 has become possible only with the recent development of isolated attosecond (10 −18 -s) laser pulses 5 . Such pulses have been used to investigate atomic photoexcitation and photoionization 6 , 7 and electron dynamics in solids 8 , and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H 2 and D 2 was monitored on femtosecond timescales 9 and controlled using few-cycle near-infrared laser pulses 10 . Here we report a molecular attosecond pump–probe experiment based on that work: H 2 and D 2 are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends—with attosecond time resolution—on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump–probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born–Oppenheimer approximation.

Until about a decade ago, laser-induced ionization was considered instantaneous. Since then, applications of attosecond laser pulses have shown multiple subtle and complex factors that influence the precise timing of electron ejection from atoms and surfaces. Vos et al. measured the corresponding attosecond dynamics of dissociative photoionization in a diatomic molecule, carbon monoxide. By imaging the charged fragments, the timing could be correlated with the specific spatial portion of the molecule from which the electron wave packet emerged. Science , this issue p. 1326 The precise timing of ionization in CO varies with respect to the portion of the molecule from which the electron emerges. Attosecond metrology of atoms has accessed the time scale of the most fundamental processes in quantum mechanics. Transferring the time-resolved photoelectric effect from atoms to molecules considerably increases experimental and theoretical challenges. Here we show that orientation- and energy-resolved measurements characterize the molecular stereo Wigner time delay. This observable provides direct information on the localization of the excited electron wave packet within the molecular potential. Furthermore, we demonstrate that photoelectrons resulting from the dissociative ionization process of the CO molecule are preferentially emitted from the carbon end for dissociative 2 Σ states and from the center and oxygen end for the 2 Π states of the molecular ion. Supported by comprehensive theoretical calculations, this work constitutes a complete spatially and temporally resolved reconstruction of the molecular photoelectric effect.