Shulou(Shulou.com)11/24 Report--

CTOnews.com January 16 news, According to the Chinese Academy of Sciences Dalian Institute of Chemistry official news, How to accurately regulate chemical reactions is one of the core goals of chemical science research. In the chemical production process, engineers can control chemical reactions to a certain extent by adding catalysts and changing macroscopic parameters such as temperature and pressure of chemical processes to obtain the desired chemical reaction products. With the understanding of chemical reaction going deep into atomic molecular scale and quantum state, how to further develop the principle and method of precise regulation of chemical reaction at microscopic level has become the goal of many scientists.

Recently, the experimental team of Academician Yang Xueming and Researcher Xiao Chunlei of Dalian Institute of Chemical Physics of Chinese Academy of Sciences (hereinafter referred to as "Dalian Institute of Chemical Physics of Chinese Academy of Sciences"), together with the theoretical team of Academician Zhang Donghui and Associate Researcher Zhang Zhaojun, has made important progress in this research direction. By controlling the direction of molecular chemical bonds, the stereodynamic precise regulation of chemical reactions has been realized. The results were published in the journal Science on January 13, Beijing time, in the form of a long research article. Reviewers praised the work as a milestone in the field of reaction dynamics.

The essence of chemical reaction is a process in which atoms, molecules and other microscopic particles collide with each other and trigger the break of old chemical bonds and the formation of new chemical bonds. Stereokinetic effect is a fundamental and important problem in chemical reactions. It concerns how the spatial orientation of reactant molecules affects the reaction process during collision. The origin of stereodynamic effects lies in the fact that reactant molecules are not simple particles, but have specific structures and shapes. For example, hydrogen molecules are made up of two hydrogen atoms joined by covalent bonds, like a "dumbbell." Thus, when another reactant collides with hydrogen, it attacks from one end of the hydrogen molecule, or directly attacks the covalent bond of the hydrogen molecule, and the reaction probability and corresponding dynamics of the two cases may show significant differences. How to utilize the stereodynamic effect in chemical reaction to realize the fine control of chemical reaction process and result is one of the frontier problems in chemical dynamics research.

Hydrogen molecules are the simplest molecules, and they are nonpolar diatomic molecules that do not easily change orientation in the process of approaching another molecule. Therefore, elementary chemical reactions involving hydrogen molecules are ideal models for studying stereodynamic effects. However, it has been difficult to experimentally prepare sufficient quantities of hydrogen molecules with specific orientations, so it is impossible to study the stereodynamic phenomena in related reactions.

In response to this challenge, Yang Xueming and Xiao Chunlei's experimental team developed a high-energy, single-longitudinal-mode nanosecond pulsed optical parametric oscillator amplifier, realizing the stereodynamic regulation of hydrogen molecules. By manipulating the polarization direction of laser photons during stimulated Raman excitation, the team prepared hydrogen molecules in specific vibrational and rotational excited states in the molecular beam, while giving the chemical bonds of hydrogen molecules a specific spatial orientation.

Fig. 1: HD molecule collides with H atom in two configurations by controlling the direction of chemical bond with laser. The z-axis is the direction of relative motion of HD molecules and H atoms. Using lasers, the team was able to prepare HD molecules in two different collision configurations: in the first configuration, the bond axes of HD are distributed parallel to the z-axis (left); in the other configuration, the bond axes of HD are distributed perpendicular to the z-axis (right). The pump light and Stokes laser light used for stimulated Raman excitation propagate along the y-axis direction, and the green and red double arrows indicate their polarization directions. Further, using the state-to-state resolution Rydberg state time of flight spectroscopy method based on extreme ultraviolet laser technology and the crossed molecular beam technology, the experimental research team carefully measured the H+HD → H2+D reaction results of two different configurations of hydrogen deuterium (HD) and hydrogen (H) atoms at three collision energies of 0.50 eV, 1.20 eV and 2.07 eV. It is found that there are significant stereodynamic differences in the quantum states and scattering angle distributions of hydrogen molecule (H2) produced.

Fig. 2: At 0.50 eV collision energy, the differential reaction cross sections of H+HD → H2+H reaction for two different collision configurations are very different (left column: measured by crossed molecular beam experiment; right column: simulated by quantum dynamics theory). The different rings represent different vibrational states of H2 molecular products, and the height of the rings represents the relative amount of H2 molecular products in the corresponding scattering direction. In order to understand the dynamic process, Zhang Donghui and Zhang Zhaojun's theoretical team carried out non-adiabatic quantum dynamics simulation, accurately reproduced the phenomena observed in the experiment, and combined with the polarization differential cross section theory method, analyzed the stereo dynamics effect existing in the reaction in detail, revealing that the quantum interference phenomenon played an important role in the vertical collision configuration reaction.

"Previous chemical reaction research may be like a 'blind box', which is determined by the original quantum properties. Researchers cannot control it at will. We can only have a certain probability to extract the desired result. "But now we can get our desired results directly by precisely controlling the excitation of a particular chemical bond and controlling its direction. "

Through high-precision experimental and theoretical studies, this work verifies that chemical reactions can be finely regulated by manipulating the spatial orientation of hydrogen molecular quantum states, indicating that human understanding and regulation of chemical reactions have reached a new height.

The co-first authors of the paper are Wang Yufeng and Huang Jiayu, postdoctoral fellows of Dalian Institute of Chemistry, Chinese Academy of Sciences. The relevant research work has been supported by the Science and Technology Innovation 2030 Major Project of the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Scientific Research Instrument and Equipment Development Project of the Chinese Academy of Sciences.

Researchers work in front of lasers that control the orientation of chemical bonds in hydrogen molecules

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