No abstract

The dynamics of the H + MgH → Mg + H2 reaction at low collision energies is analyzed with both quasi-classical trajectory and quantum wave packet methods on an improved potential-energy surface for the ground electronic state of MgH2. Three microscopic reaction channels, namely, direct abstraction, roaming via a loose roaming transition state, and complex decaying via a tight transition state, are identified. It is shown that the reaction is dominated at low collision energies by the direct abstraction channel, whereas the roaming channel is responsible for about 20% of the reaction flux. The pathway via the tight transition state plays almost no role at the energy of study. The two dominant channels produce similar highly excited vibrational distributions for the H2 product. Finally, it is shown that roaming is manifested quantum-mechanically by a large-amplitude vibration that emerges just below the reaction threshold and is guided by the roaming transition state. Its continuation into the continuum leads to roaming resonances.

Molecular vibration often impacts chemical reactions; however, for substitution reactions, we present here a spectator mode.

The reactions of FeO + with H 2 , D 2 , and HD were studied in detail from 170 to 670 K by employing a variable temperature selected ion flow tube apparatus. High level electronic structure calculations were performed and compared to previous theoretical treatments. Statistical modeling of the temperature and isotope dependent rate constants was found to reproduce all data, suggesting the reaction could be well explained by efficient crossing from the sextet to quartet surface, with a rigid near thermoneutral barrier accounting for both the inefficiency and strong negative temperature dependence of the reactions over the measured range of thermal energies. The modeling equally well reproduced earlier guided ion beam results up to translational temperatures of about 4000 K.