A research group led by Prof. ZHANG Donghui and Associate Prof. LIU Shu from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences revealed Feshbach Resonances in the F+H₂O→HF+OH reaction. The results were published in Nature Communications. 

Feshbach resonances of a chemical reaction are transiently trapped quantum states along the reaction coordinate in the transition-state region. They not only have a profound influence on both the rate and product distribution, but also provide sensitive probes to the potential energy surface (PES) of the reaction. 

(A) Scattering wave functions; (B) vibrational adiabatic potentials analyses. (Image by LIU Shu) 

Through close interactions between theory and experiment, our understanding of the Feshbach resonances in triatomic reaction such as the F/Cl+H₂ (HD) reactions is now highly sophisticated. The study of resonance is now naturally extending to systems involving more than three atoms. The F+H₂O reaction has emerged as the benchmark system for such a purpose. 

Similar to the F+H₂ system, the F+H₂O→HF+OH reaction is highly exothermic and has a low and "early" barrier on the ground electronic state. 

In an earlier photodetchment study of FH₂O^？, Feshbach resonances have been discovered trapped in the HF-OH interaction well. However, it is not clear if these resonances are accessible by the F+H₂O reaction and how these resonances affect the reaction. 

ZHANG’s group performed an accurate state-to-state quantum scattering study of the F+H₂O→HF+OH reaction by using the time-dependent wave packet method on an accurate newly constructed PES. The total reaction probabilities exhibited many pronounced oscillatory structures especially for collision energy below 0.2 eV. 

Analysis of scattering wave functions and vibrational adiabatic potentials (VAP) revealed that these oscillating structures originated from the Feshbach resonance states trapped in the HF(v’=2)-OH VAP well, producing mainly HF(v’=1) product. 

However, different from the F+H₂ reaction in which the HF bond softening creates a peculiar well on the H-HF(v’=3) VAP, the VAP well for the F+H₂O reaction is mainly hydrogen bond between HF and OH in nature.