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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.

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.

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 variations in Lyα forest opacity observed at z > 5.3 between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this excess variance is a late, ongoing reionization process at redshifts below six. Another model proposes strong ionizing background fluctuations coupled to a short, spatially varying mean free path of ionizing photons, without explicitly invoking incomplete reionization. With recent observations suggesting a short mean free path at z ∼ 6, and a dramatic improvement in z > 5 Lyα forest data quality, we revisit this latter possibility. Here, we apply the likelihood-free inference technique of approximate Bayesian computation (ABC) to jointly constrain the hydrogen photoionization rate ΓHI and the mean free path of ionizing photons λ mfp from the effective optical depth distributions at z = 5.0–6.1 from XQR-30. We find that the observations are well-described by fluctuating mean free path models with average mean free paths that are consistent with the steep trend implied by independent measurements at z ∼ 5–6, with a concomitant rapid evolution of the photoionization rate.

We examine the factors responsible for the variation in the ionization parameter (U) of high-redshift star-forming galaxies based on medium-resolution JWST/NIRSpec observations obtained by the Cosmic Evolution Early Release Science survey. The sample consists of 48 galaxies with redshifts z spec = 2.7−6.3, which are largely representative of typical galaxies at these redshifts. The [S ii] λ λ6718, 6733 doublet is used to estimate electron densities (n e ), and dust-corrected Hα luminosities are used to compute ionizing photon rates (Q). Using composite spectra of galaxies in bins of [O iii] λ λ4960, 5008/[O ii] λ λ3727, 3730 (O32) as a proxy for U, we determine that galaxies with higher O32 have 〈n e 〉 ≃ 500 cm−3 that are ≳5 × larger than that of lower-O32 galaxies. We do not find a significant difference in 〈Q〉 between low- and high-O32 galaxies. Photoionization modeling indicates a large spread in logU of ≈1.5 dex at a fixed Z neb. On the other hand, the data indicate a highly significant correlation between U and star-formation-rate surface density (ΣSFR), which appears to be redshift invariant at z ∼ 1.6−6.3, and possibly up to z ∼ 9.5. We consider several avenues through which metallicity and ΣSFR (or gas density) may influence U, including variations in n e and Q, internal dust extinction of ionizing photons, and the effects of gas density on the volume filling fraction. Based on these considerations, we conclude that gas density may play a more central role than metallicity in modulating U at these redshifts.

We present the z ≈ 6 type-1 quasar luminosity function (QLF), based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars at z ≈ 5.7–6.2, with −28 ≲ M 1450 ≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate the z ≈ 6 QLF over −28 ≲ M 1450 ≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z) ∝ 10 k(z−6); k = −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of M*=−26.38−0.60+0.79mag , a faint-end slope of α=−1.70−0.19+0.29 , and a steep bright-end slope of β=−3.84−1.21+0.63 . Based on our new QLF model, we determine the quasar comoving spatial density at z ≈ 6 to be n(M1450<−26)=1.16−0.12+0.13cGpc−3 . In comparison with the literature, we find the quasar density to evolve with a constant value of k ≈ −0.7, from z ≈ 7 to z ≈ 4. Additionally, we derive an ionizing emissivity of ϵ912(z=6)=7.23−1.02+1.65×1022ergs−1Hz−1cMpc−3 , based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. at z ≈ 6, we calculate an H i photoionizing rate of ΓH I(z = 6) ≈ 6 × 10−16 s−1, strongly disfavoring a dominant role of quasars in hydrogen reionization.

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.

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.

The first JWST spectroscopy of the luminous galaxy GN-z11 simultaneously established its redshift at z = 10.6 and revealed a rest-ultraviolet spectrum dominated by signatures of highly ionized nitrogen, which has so far defied clear interpretation. We present a reappraisal of this spectrum in the context of both detailed nebular modeling and nearby metal-poor reference galaxies. The N iv] emission enables the first nebular density measurement in an apparently predominantly star-forming galaxy at z > 10, revealing evidence for extremely high densities n e ≳ 105 cm−3. With a suite of photoionization models, we establish that regardless of the ionization mechanism and accounting for depletion and this density enhancement, gas substantially enriched in nitrogen ([N/O] = +0.52 assuming the nebular emission is dominated by star formation) is required to reproduce the observed lines. We compare the GN-z11 spectrum to local UV databases and highlight a unique nearby galaxy, Mrk 996, where a high concentration of Wolf–Rayet stars and their CNO-processed ejecta produce a UV spectrum remarkably similar in some respects to that of GN-z11 and the Sunburst Arc. Collating this evidence in the context of Galactic stellar abundances, we suggest that the peculiar nitrogenic features prominent in GN-z11 may be a unique signature of intense and densely clustered star formation in the evolutionary chain of the present-day globular clusters, consistent with in situ early enrichment with nuclear-processed stellar ejecta on a massive scale. Combined with insight from local galaxies, these and future JWST data open a powerful new window into the physical conditions of star formation and chemical enrichment at the highest redshifts.

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.