Periodic Reporting for period 1 - HRICOMC (High-resolution imaging of cold and controlled molecular collisions using recoil-free resonance-enhanced multiphoton ionization detection schemes)
Periodo di rendicontazione: 2020-10-01 al 2022-09-30
The study of collisions between cold molecules has attracted much attention in recent years. This research could enable us to understand the most fundamental aspects of molecular interactions and the progress of this research makes it possible to achieve the goal of manipulation and control of chemical reactions. Furthermore, the full understanding of cold molecular collisions could shed new light on some important puzzles in the Earth’s atmospheric and interstellar chemistry. However, to date, the study of cold molecular collisions remains largely unexplored, due to a huge challenge in the experimental approach. For instance, techniques for obtaining high-quality molecular beams and high-resolution state-to-state resolved detection for the crossed molecular beam experiment are rarely available.
In this project, we used a new crossed-beam scattering experimental method combined with a multistage Zeeman decelerator and recoil-free resonance-enhanced multiphoton ionization (REMPI) detection schemes, which allowed us to investigate the dynamics of cold and controlled molecular collisions with unprecedented resolution in a new, previously inaccessible, regime.
We successfully combined Zeeman deceleration and Vacuum-Ultraviolet detection (VUV) based recoil-free REMPI detection and upgraded our setup to reach previously inaccessible collision energies by reducing the crossed beam angle to only 4 degrees. Using this experimental approach, we investigated scattering resonance effects for C + He, H2 inelastic collisions. We measured angular scattering distributions of the scattered C atoms and found that the differential cross section (DCS) changes rapidly as a function of collision energy when the C atoms collided with H2 molecules. These measurements provided a very sensitive test for the potential energy surfaces that describe the interactions between the colliding particles. Afterwards, we successfully investigated the reactive collision between electronically excited sulfur atoms and hydrogen molecules. We for the first time measured quantum-state-resolved scattering images of the reaction products for this reaction.
Our results have provided and will provide a critical test for current models of chemical processes taking place in the Earth's atmosphere and in interstellar space. In the future, we hope to be able to manipulate and control chemical reactions based on the knowledge gained during this project.
In this project, we used a new crossed-beam scattering experimental method combined with a multistage Zeeman decelerator and recoil-free resonance-enhanced multiphoton ionization (REMPI) detection schemes, which allowed us to investigate the dynamics of cold and controlled molecular collisions with unprecedented resolution in a new, previously inaccessible, regime.
We successfully combined Zeeman deceleration and Vacuum-Ultraviolet detection (VUV) based recoil-free REMPI detection and upgraded our setup to reach previously inaccessible collision energies by reducing the crossed beam angle to only 4 degrees. Using this experimental approach, we investigated scattering resonance effects for C + He, H2 inelastic collisions. We measured angular scattering distributions of the scattered C atoms and found that the differential cross section (DCS) changes rapidly as a function of collision energy when the C atoms collided with H2 molecules. These measurements provided a very sensitive test for the potential energy surfaces that describe the interactions between the colliding particles. Afterwards, we successfully investigated the reactive collision between electronically excited sulfur atoms and hydrogen molecules. We for the first time measured quantum-state-resolved scattering images of the reaction products for this reaction.
Our results have provided and will provide a critical test for current models of chemical processes taking place in the Earth's atmosphere and in interstellar space. In the future, we hope to be able to manipulate and control chemical reactions based on the knowledge gained during this project.
At the start of the project, we successfully set up the molecular machine for developing the VUV-based REMPI technique. A series of experiments demonstrated for the first time that the recoil-free REMPI detection schemes for different chemically relevant species such as carbon, oxygen atoms can be obtained with VUV light. The recoil-free detection methods for H, O, C atoms lay an important foundation for the following research work. One paper was published in a peer-reviewed journal.
Afterwards, we investigated C + He collisions and found that the combination of Zeeman deceleration and VUV-based recoil-free REMPI detection allows us to achieve high-resolution imaging. We further confirmed that not only the resolution but also the sensitivity of this VUV detection method is sufficient for high-resolution inelastic scattering experiments. After upgrading the setup to reach previously inaccessible collision energies by reducing the crossed beam angle to only 4 degrees, we studied the resonance effects of C + He, H2 inelastic collisions, and found the differential cross section (DCS) changes rapidly as a function of collision energy. Our results have provided a critical and sensitive test for current models of theory. One paper was published in a peer-reviewed journal and one journal paper is being prepared. One talk with the title of “Cold and controlled inelastic and reactive collisions between C and O2” has been presented in the 29th International Symposium on Molecular Beams and a few posters have been presented in conferences.
Finally, we started investigating the S+D2 → SD + D reaction. This is much more challenging to investigate than the inelastic scattering processes studied before, since, for instance, the signal levels are expected to be much lower. We managed to see the first reactive scattering signals using the Zeeman decelerator, and we measured the first quantum-state-resolved angular scattering distributions of the products. This research will be continued after the end of this project. One talk with the title of “Exploring the full potential of a Zeeman decelerator: from inelastic scattering to chemical reactions” will be presented in November in sIMMposium 2022.
Afterwards, we investigated C + He collisions and found that the combination of Zeeman deceleration and VUV-based recoil-free REMPI detection allows us to achieve high-resolution imaging. We further confirmed that not only the resolution but also the sensitivity of this VUV detection method is sufficient for high-resolution inelastic scattering experiments. After upgrading the setup to reach previously inaccessible collision energies by reducing the crossed beam angle to only 4 degrees, we studied the resonance effects of C + He, H2 inelastic collisions, and found the differential cross section (DCS) changes rapidly as a function of collision energy. Our results have provided a critical and sensitive test for current models of theory. One paper was published in a peer-reviewed journal and one journal paper is being prepared. One talk with the title of “Cold and controlled inelastic and reactive collisions between C and O2” has been presented in the 29th International Symposium on Molecular Beams and a few posters have been presented in conferences.
Finally, we started investigating the S+D2 → SD + D reaction. This is much more challenging to investigate than the inelastic scattering processes studied before, since, for instance, the signal levels are expected to be much lower. We managed to see the first reactive scattering signals using the Zeeman decelerator, and we measured the first quantum-state-resolved angular scattering distributions of the products. This research will be continued after the end of this project. One talk with the title of “Exploring the full potential of a Zeeman decelerator: from inelastic scattering to chemical reactions” will be presented in November in sIMMposium 2022.
This project has pushed the frontiers of the research field of chemical reaction dynamics forward by the combination of two advanced techniques which are Zeeman deceleration and state-selective threshold ionization based on VUV. For the first time, we developed recoil-free threshold ionization detection methods for C, O atoms that can be used in crossed-beam scattering experiments employing a decelerator. The fellow transferred knowledge of the four-wave mixing method for generating VUV light to his colleagues. Also, for the first time, we successfully combined the Zeeman decelerator and VUV-based recoil-free threshold ionization detection methods to investigate the inelastic scattering of C + He, and C + H2 in unexplored energy regimes. These high-resolution experimental results challenge the current theory, allowing us to test theoretical models of the interactions between the colliding species. Although the density of a decelerated molecular beam is low compared to the density of a conventional molecular beam, we for the first time used our Zeeman decelerator to investigate reactive collisions, paving the way to better understand and eventually even control chemical reaction processes in the future.