Researchers have achieved a significant breakthrough in the field of quantum mechanical control of chemical reactions. By utilizing a combination of two extreme-ultraviolet (XUV) light sources, they were able to selectively excite a molecule, causing it to dissociate while simultaneously tracking its progress over time. This advancement holds great potential in enabling new reaction channels and expanding our understanding of chemical processes at a quantum level. In this article, we will delve deeper into the significance of this achievement and its implications for future research.
Light-matter interaction is a fundamental aspect of various natural phenomena, including biological processes like photosynthesis. Solar cells also heavily rely on this process. However, on the Earth’s surface, only visible, ultraviolet, and infrared light plays a role in these interactions. Extreme-ultraviolet (XUV) light, which possesses significantly higher energy than visible light, is absorbed by the atmosphere and does not reach the Earth’s surface. Nonetheless, XUV radiation can be produced and utilized in laboratory settings to selectively excite electrons in molecules, subsequently enabling new chemical reaction processes that do not occur naturally.
A team of researchers led by PD Dr. Christian Ott from the Max-Planck-Institut für Kernphysik in Heidelberg, Germany, has made a groundbreaking achievement by successfully combining two different XUV light sources. This allowed them to temporally resolve a quantum mechanical dissociation mechanism in oxygen molecules. In their study published in the journal Science Advances, the researchers utilized laser pulses generated through high harmonic generation (HHG) and a free-electron laser (FEL).
High harmonic generation is a process in which infrared light is passed through a gas cell, converting it into XUV radiation. This technique has gained recognition, as evidenced by its inclusion in the 2018 Nobel Prize in Physics. HHG pulses have a broad spectrum, consisting of light with various frequencies or “colors.” These pulses played a crucial role in capturing the resulting fragments of the dissociated oxygen molecules through spectral absorption fingerprints, resembling a fast photo series.
The researchers also employed a free-electron laser (FEL) to excite the electrons of the oxygen molecule to a specific state. The FEL pulses emitted from the accelerated electrons have a more limited spectral range compared to HHG pulses. This narrower spectrum provides the researchers with the ability to initiate targeted electronic or molecular processes and independently gather a wide range of quantum-mechanical state information about the molecule and its fragments using HHG spectra.
One of the significant challenges that the researchers sought to address was understanding the speed at which molecular dissociation occurs in oxygen molecules. Two different channels have been identified through which these molecules dissociate when in a specific state. However, the precise speed at which these dissociation processes occur has remained elusive due to the quantum tunneling process involved. By introducing a second HHG pulse with a adjustable time delay after the initial exciting FEL pulse, the researchers were able to experimentally record the molecular dissociation process. The time delay determines the number of molecules that have already decayed, with an increased number of fragments indicating a longer duration of the process.
This breakthrough discovery opens up new possibilities for recording, understanding, and ultimately controlling more complex chemical reactions with light. The ability to selectively excite molecules and track their quantum-mechanical behavior enables researchers to gain deeper insights into the fundamental mechanisms underlying chemical reactions. Furthermore, the potential for expanding these techniques to other molecules and reaction systems holds promise for the development of innovative applications in fields such as organic synthesis, material science, and drug discovery.
The achievement of selectively exciting a molecule using a combination of two XUV light sources marks a significant milestone in the field of quantum mechanical control of chemical reactions. By gaining the ability to observe and manipulate chemical reactions at the quantum level, researchers can uncover new reaction pathways and further our understanding of the intricate dynamics governing molecular transformations. As future advancements build upon this breakthrough, we can expect to witness even more profound insights into the world of chemical reactions and the potential for novel applications in various scientific disciplines.
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