The reaction of fluorine atoms with hydrogen molecules has long provided a window into the subtle effects of quantum mechanics on chemical dynamics. Kim et al. now show that the system still has some secrets left to reveal. The authors applied photodetachment to FH2− anions and their deuterated analogs. This allowed them to intercept the reaction trajectory in the middle and thereby uncover unanticipated weakly bound resonances. Theoretical calculations explain these observations and predict additional similar features that have yet to be seen.
Science, this issue p. 510
The degree of electronic and nuclear coupling in the Cl + H2 reaction has become a vexing problem in chemical dynamics. We report slow electron velocity-map imaging (SEVI) spectra of ClH2– and ClD2–. These spectra probe the reactant valley of the neutral reaction potential energy surface, where nonadiabatic transitions responsible for reactivity of the Cl excited spin-orbit state with H2 would occur. The SEVI spectra reveal progressions in low-frequency Cl·H2 bending and stretching modes, and are compared to simulations with and without nonadiabatic couplings between the Cl spin-orbit states. Although nonadiabatic effects are small, their inclusion improves agreement with experiment. This comparison validates the theoretical treatment, especially of the nonadiabatic effects, in this critical region of the Cl + H2 reaction, and suggests strongly that these effects are minor.
