Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold ...of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.
Autoionization, which results from the interference between direct photoionization and photoexcitation to a discrete state decaying to the continuum by configuration interaction, is a well known ...example of the important role of electron correlation in light-matter interaction. Information on this process can be obtained by studying the spectral, or equivalently, temporal complex amplitude of the ionized electron wave packet. Using an energy-resolved interferometric technique, we measure the spectral amplitude and phase of autoionized wave packets emitted via the sp2+ and sp3+ resonances in helium. These measurements allow us to reconstruct the corresponding temporal profiles by Fourier transform. In addition, applying various time-frequency representations, we observe the build-up of the wave packets in the continuum, monitor the instantaneous frequencies emitted at any time and disentangle the dynamics of the direct and resonant ionization channels.
The dynamics of quantum systems are encoded in the amplitude and phase of wave packets. However, the rapidity of electron dynamics on the attosecond scale has precluded the complete characterization ...of electron wave packets in the time domain. Using spectrally resolved electron interferometry, we were able to measure the amplitude and phase of a photoelectron wave packet created through a Fano autoionizing resonance in helium. In our setup, replicas obtained by two-photon transitions interfere with reference wave packets that are formed through smooth continua, allowing the full temporal reconstruction, purely from experimental data, of the resonant wave packet released in the continuum. In turn, this resolves the buildup of the autoionizing resonance on an attosecond time scale. Our results, in excellent agreement with ab initio time-dependent calculations, raise prospects for detailed investigations of ultrafast photoemission dynamics governed by electron correlation, as well as coherent control over structured electron wave packets.
Synopsis In contrast to one-photon transitions and non-resonant multiphoton transitions, time delay in resonant multi-photon electron emission can exhibit large positive and negative values that have ...no scattering equivalent, due to the interference of multiple ionization paths.
Moving towards a more sustainable energy system is a major goal of modern societies that aim to minimize the dependence on fossil fuels and the associated anthropogenic impacts. In this article, the ...combined use of Life Cycle Assessment (LCA) and Data Envelopment Analysis (DEA) is applied to analyse the environmental performance (eco-efficiency) of the electricity mix of the top European economies. This approach allows identifying environmentally efficient and inefficient countries considering as undesirable inputs several environmental impacts associated with the production of 1 kWh (regarded as output). The method provides as well targets for the inefficient countries that (if attained) would make them efficient. Our results provide valuable insight for governments and policy makers that aim to satisfy the electricity demand while minimizing the associated environmental impact.
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•We analyze the eco-efficiency of the electricity mix of the top 27 European economies.•Moving toward ecofriendly electricity production mixes is the goal of this study.•The targets for eco-inefficient countries are provided and compared with actual mixes.•The study focuses on satisfying the electricity demand with minimum environmental impact.•Our approach provides useful guidelines for governments on how to improve the environmental performance of energy generation.
High-harmonic generation is typically thought of as a sub-laser-cycle process, with the electron’sexcursion in the continuum lasting a fraction of the optical cycle. However, it was recently ...suggested thatlong-lived Rydberg states can play a particularly important role in high harmonic generation by atomsdriven by the combination of the counterrotating circularly polarized fundamental light field and its secondharmonic. Here we report direct experimental evidence of very long and stable Rydberg trajectoriescontributing to high-harmonic generation in such fields. We track their dynamics inside the laser pulseusing the spin-orbit evolution in the ionic core, utilizing the spin-orbit Larmor clock. We confirm theireffect on harmonic emission both via microscopic simulations and by showing how this radiation can leadto a well-collimated macroscopic far-field signal. Our observations contrast sharply with the general viewthat long-lived Rydberg orbits should generate negligible contribution to the macroscopic far-field highharmonic response of the medium
Synopsis We present a theoretical study of the photoelectron attosecond beating due to interference of two- photon transitions in the presence of autoionizing states. We show that, as a harmonic ...traverses a resonance, both the phase and frequency of the sideband beating significantly vary with photon energy. Furthermore, the beating between two resonant paths persists even when the pump and probe pulses do not overlap, thus permitting to reconstruct nonholographically coherent metastable wave packets. We characterize these phenomena with an analytical model that accounts for the effect of both intermediate and final resonances on two-photon processes.
Zeolite-based adsorbents have been successfully used for many challenging separations due to their tunable properties. A particularly notable application involves the separation of light olefins from ...paraffins, wherein the molecular sieving properties of zeolites play a pivotal role. Additionally, the selective interaction of alkenes with transition metal cations, positioned within the channels and cavities of microporous zeolites, further enhances separation capabilities.
This study aims to comprehensively characterize the interactions between ethylene and Ag+ exchanged zeolites, employing a multidisciplinary approach, combining Inelastic Neutron Scattering (INS), Infrared (IR) spectroscopy, Nuclear Magnetic Resonance (NMR), UV–Vis and Density Functional Theory (DFT) calculations. CHA and RHO, zeolites largely applied in gas separation processes, were chosen due to their similar small pore sizes and pore volume, but different cavity shapes and flexibilities.
The interpretation of derived DFT Electron Density Difference, experimentally supported by 13C Solid State NMR results, provide an understanding of each framework’s role during the charge transfer mechanisms between ethylene and transition metal species. Specific deformations in the flexible framework of zeolite RHO explain a blueshift of the band at 400 cm−1 in the librational region of INS spectra compared to CHA. This structural change in RHO, represented by the conic shape of the cage 8-ring side pockets, increases steric effects over the adsorbate while rendering the metallic adsorption center less exposed within the zeolite’s cavity, finally leading to a weaker adsorption energy. The redshift of C=C stretching frequencies observed by IR spectroscopy and DFT calculations, as well as C=C and C-H bond lengthening of ethylene confirm the formation of π-complexes on silver in both zeolites and allowed a further evaluation of the effects of the different frameworks cages on the aforementioned interaction.
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•Ethylene forms a π complex with Ag+ species in Ag-zeolites as proved by INS and DFT.•The π complex is accommodated in the cages 8-ring side pockets.•CHA’s pocket is less constricted than deformed RHO’s pocket.•The denser electrostatic field around Ag+ in RHO leads to a weaker adsorption.•Framework geometry and flexibility play an important role in π complexation.
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