With the support of the National Natural Science Foundation of China (Grant No. 21688102, 21590800, 21733006, 21825303, 21327901), Professor Xingan Wang’s group (University of Science and Technology of China) ,in cooperation with the research group of Professor Zhigang Sun and Professor Xueming Yang (Dalian Institute of Chemical Physics, Chinese Academy of Sciences), observed the quantum interference between spin-orbit split partial waves in a fundamental chemical reaction for the first time, and revealed the important influences of electron spin-orbit interactions on chemical reaction dynamics. This work titled “Quantum interference between spin-orbit split partial waves in the F+HD→HF+D reaction” was published online in Science on Feb. 26, 2021. (Science 2021, 371, 936-940; https://science.sciencemag.org/content/371/6532/936)

Since electron spin was discovered by Uhlenbeck and Goudsmit in 1925, it has been found that the couplings between electron spin and orbital angular momentum could induce many interesting phenomena, such as the splitting of atomic energy levels, magnetocrystalline anisotropy, quantum spin Hall effect in semiconductors, etc. In a chemical reaction, the couplings between electron spin and orbital angular momentum result in the splitting of partial waves which may yield some fine structures of partial waves. However, whether and how these couplings can affect the dynamics process of a chemical reaction remains unknown.

Very recently, the effect of the couplings between electron spin and orbital angular momentum in F+HD→HF+D reaction has been systematically studied by combining the experimental and theoretical approaches. Experimentally, a newly developed high-resolution velocity imaging crossed-beams technique with near threshold ionization of the D-atom product was applied to measure the angular and translational energy distribution in a very high resolution. This apparatus allowed to acquire rotational state-resolved differential cross sections of the products from F (²P_3/2) + HD (v=0, j=0) reaction. Based on the highly resolved experimental results, a peculiar “horseshoe” pattern (Fig.1) was clearly observed in the product rotational state-resolved differential cross sections around the forward-scattering direction. Theoretically, a new quantum reactive scattering theory based on the couplings of electron spin and orbital angular momentum was developed. Theoretical results revealed that the “horseshoe” pattern was largely from quantum interference between spin-orbit split-partial-wave resonances with positive and negative parities. Although the energy of electron spin angular momentum is much smaller than that of vibration and rotation of molecule, the influences of the couplings of electron spin-orbit interactions on chemical reaction dynamics has been clearly observed for the first time, which is an important breakthrough in the field of molecular reaction dynamics.

This work provides a distinctive example of how spin-orbit interactions can effectively influence the reaction dynamics. It is beneficial for reaction dynamics and precision measurements in chemistry.

Fig.1 left, Experimental image and the “horseshoe” pattern; right, Schematic of the reaction mechanism.