Experiment And Theory Agree On Triatomic Reaction

Differences between theory and experiment on the mechanism of the triatomic reaction of Cl and H₂ to form HCl plus H have frustrated researchers in the past. Now, molecular beam experiments have resolved those differences by showing that theory and experiment do agree. The work was carried out by Xueming Yang and Dong H. Zhang at the Chinese Academy of Sciences, in Dalian; Daiqian Xie of Nanjing University, in China; Millard H. Alexander of the University of Maryland; and coworkers (Science 2008, 322, 573). The Born-Oppenheimer approximation predicts low reactivity of excited-state Cl in the reaction, whereas some experiments had indicated that Cl reactivity would increase substantially with increasing collision energy. The new molecular beam experiments show that excited-state Cl has low reactivity, supporting theory. This high level of agreement between theory and experiment suggests that the accuracy with which triatomic reactions can now be modeled is approaching that formerly achieved only for simpler reactions, the researchers note.