Periodic Reporting for period 4 - eDrop (Droplet Photoelectron Imaging)
Periodo di rendicontazione: 2024-05-01 al 2025-10-31
Angle-resolved photoelectron spectroscopy of aerosol droplets (“droplet photoelectron imaging”) is a novel approach to study fundamental aspects of the electron dynamics in liquids and across interfaces. Our recent proof-of-principle studies demonstrated that droplet photoelectron imaging not only complements, but also significantly extends the range of accessible information over established methods. Two aspects are unique to droplets: Firstly, the droplet size can be varied over a wide range from submicrons to microns. While large droplets provide overlap with liquid microjet and bulk studies, small droplets offer additional control by acting as efficient optical resonators. These optical cavity effects can be exploited to control where in the droplet the photoelectrons are generated; e.g. surface versus volume. Secondly, comprehensive information about photoelectron kinetic energy and angular distributions can be obtained fast and in a straightforward way by velocity map imaging.
Building on our proof-of-principle studies, we proposed to exploit the versatility of the droplet approach to address fundamental questions regarding electron dynamics in liquids and across interfaces: Can this new tool provide the missing data for low-energy electron scattering in water and other liquids and resolve the issue of the “universal curve”? How do slow electrons scatter across liquid-gas and buried liquid-liquid/solid interfaces and how does this depend on the composition and curvature of the interface? How is the ultrafast relaxation dynamics of electrons upon above-band-gap excitation influenced by electron scattering and confinement effects? Low-energy electron scattering is a determining factor in radiation chemistry and biology and a central aspect of the solvated electron dynamics, while interfacial processes play a key role in atmospheric aerosols.
This project has established droplet photoelectron imaging as a novel tool that is complementary to liquid microjet and bulk phase photoelectron spectroscopy. With this new tool it was possible to answer the above fundamental questions about low-energy electron scattering in liquids and across liquid interfaces. Previously unknown ultrafast relaxation pathways for electrons in liquids have been discovered. The influence of confinement effects on processes in droplets has been unraveled.
Building on our proof-of-principle studies, we proposed to exploit the versatility of the droplet approach to address fundamental questions regarding electron dynamics in liquids and across interfaces: Can this new tool provide the missing data for low-energy electron scattering in water and other liquids and resolve the issue of the “universal curve”? How do slow electrons scatter across liquid-gas and buried liquid-liquid/solid interfaces and how does this depend on the composition and curvature of the interface? How is the ultrafast relaxation dynamics of electrons upon above-band-gap excitation influenced by electron scattering and confinement effects? Low-energy electron scattering is a determining factor in radiation chemistry and biology and a central aspect of the solvated electron dynamics, while interfacial processes play a key role in atmospheric aerosols.
This project has established droplet photoelectron imaging as a novel tool that is complementary to liquid microjet and bulk phase photoelectron spectroscopy. With this new tool it was possible to answer the above fundamental questions about low-energy electron scattering in liquids and across liquid interfaces. Previously unknown ultrafast relaxation pathways for electrons in liquids have been discovered. The influence of confinement effects on processes in droplets has been unraveled.
Light interacts differently with small droplets compared with extended condensed matter because of the finite size of these droplets. This also modifies light-induced processes, such as the formation and transport of electrons or chemical reactions. To investigate such phenomena, a novel droplet photoelectron spectrometer with a femtosecond high harmonic laser light source was built, tested and its performance characterized as documented in a series of scientific publications.
Exploiting such finite-size effects enabled us to retrieve accurate information about how slow electrons lose energy and change their direction when they travel through liquid water. Accurate cross sections for low-energy electron scattering in liquid water were made available to the public in a series of scientific publications. Detailed knowledge of electron scattering in water is, for example, crucial for a better understanding of energy dissipation processes that are relevant to radiation chemistry and biology.
The hydrated electron is a species that is supposed to play an important role in the chain of radiation damage processes in biological material. Hence, knowledge of its electronic properties and about its formation upon excitation of aqueous systems by light are important to assess its role in radiation damage. Additionally, the influence of spatial confinement on those properties needs to be assessed. We performed a series of experimental studies, revealing that spatial confinement has no major influence on the electronic properties nor on the relaxation dynamics of the hydrated electron. However, a clear system size dependence was observed for its probability of formation. In the course of our studies, we discovered a previously unknown relaxation process that offers a way to produce slow electrons in a controlled way by excitation with ultraviolet light. All these results have been documented in scientific publication.
Because of the finite size of aerosol particles, sunlight is amplified in their interior. Our investigations have shown that all light-induced reaction steps in atmospheric aerosol particles take place about 3 times faster than in the bulk liquid as a result of the light amplification. Our findings have been published in a scientific article and will have important implications regarding the role of such light induced processes in atmospheric processes.
Exploiting such finite-size effects enabled us to retrieve accurate information about how slow electrons lose energy and change their direction when they travel through liquid water. Accurate cross sections for low-energy electron scattering in liquid water were made available to the public in a series of scientific publications. Detailed knowledge of electron scattering in water is, for example, crucial for a better understanding of energy dissipation processes that are relevant to radiation chemistry and biology.
The hydrated electron is a species that is supposed to play an important role in the chain of radiation damage processes in biological material. Hence, knowledge of its electronic properties and about its formation upon excitation of aqueous systems by light are important to assess its role in radiation damage. Additionally, the influence of spatial confinement on those properties needs to be assessed. We performed a series of experimental studies, revealing that spatial confinement has no major influence on the electronic properties nor on the relaxation dynamics of the hydrated electron. However, a clear system size dependence was observed for its probability of formation. In the course of our studies, we discovered a previously unknown relaxation process that offers a way to produce slow electrons in a controlled way by excitation with ultraviolet light. All these results have been documented in scientific publication.
Because of the finite size of aerosol particles, sunlight is amplified in their interior. Our investigations have shown that all light-induced reaction steps in atmospheric aerosol particles take place about 3 times faster than in the bulk liquid as a result of the light amplification. Our findings have been published in a scientific article and will have important implications regarding the role of such light induced processes in atmospheric processes.
The new approach of droplet photoelectron imaging has enabled us to obtain previously inaccessible information on light-induced processes in liquids. Progress beyond the state of the art was achieved in the following directions: (i) The retrieval of low-energy electron scattering data for liquid water now enables accurate electron scattering simulations for a better assessment of radiation damage in biological systems and for a more detailed analysis of electronic properties of solutes on the basis of liquid phase photoelectron spectroscopy. (ii) The discovery of an ultrafast relaxation process of electrons in liquids provides a new avenue to the targeted production of low-energy electrons in liquids by excitation with commercial ultraviolet light sources. (iii) The quantification of the general acceleration of light-induced chemical reactions in aerosol particles by a factor of about three is a discovery that will significantly advance the modeling of atmospheric aerosol chemistry, likely changing the perception of the importance of these processes in the atmosphere.