Anomalous HF product rotational distributions in the F + H2 reaction at threshold collision energies

Abstract

Time-of-Ñight spectra for the reaction have been measured for the Ðrst time at F ] H 2 ] HF(v f , j f ) ] H collision energies less than 80 meV (1.84 kcal mol~1). The results at 70 meV, 55 meV and 36 meV at a Ðxed laboratory scattering angle have been transformed to the center-of-mass system and reveal sharp product rotational distributions for the and product vibrational states with most probable values of v f \ 1 v f \ 2 Such large values of can only be explained in terms of a substantial antiparallel orientation of the j f P 11. j f Ðnal rotational and orbital angular momenta, consistent with a long-lived collision complex or a quantum mechanical resonance. Moreover the sizeable signal at 36 meV when compared with ab initio calculations of the activation barrier at 50 meV suggests a signiÐcant tunneling e †ect.

The HF(v'=3) forward scattering peak of the F + H2 reaction revisited

“…Although the cross sections for the formation of the HF product from the F+H 2 reaction in the ground vibrational state are very small, HF(v ′ = 0) molecules have been detected in a crossed molecular beam experiment [43]. Our analysis shows that the vibrationally specific forward peak of the HF(v ′ = 3) product can be explained by the superposition of two independent effects which reinforce each other.…”

Vibrational−Rotational Energy Distributions in the Reaction O− + D2 → OD + D−

“…There are a number of reports of simple chemical reactions in which the dynamics produce bimodal rotational distributions. The well-studied F + H 2 reaction produces bimodal rotational distributions that are thought to be associated with dynamical resonances. − The possibility of multiple collisions, in which O − first collides with the first D atom, retreats nonreactively, and then reacts with the second D atom, an idea advanced by Polanyi early in the history of molecular reaction dynamics, may also provide a plausible explanation for this behavior. Another important mechanism for producing bimodal rotational distributions is the participation of more than one electronic potential energy curve/surface, such that each branch of the rotational distribution is governed by motion on different potential curves. , There are features of the O − + D 2 system that suggest the plausibility of such a mechanism in the present system.…”