Revealing umbrella bending as a reporter mode in the D+CH₄ reaction

How the non-reacting moiety of a molecule influences a polyatomic reaction has been a topic of much research interest. Here we present a comprehensive investigation of the D + CH₄ → HD + CH₃ reaction, a benchmark polyatomic elementary reaction with CH₃ as the non-reacting moiety, employing a high-resolution crossed molecular beams apparatus and an accurate seven-dimensional wave packet method. An interesting angular distribution of the CH₃(v' = 1) product umbrella bending vibrational state is observed to scatter more in the sideways direction than the CH₃(v' = 0) one. By monitoring the wave functions on a dividing surface in the transition state region, the CH₃ umbrella bending mode is established as a reporter mode that faithfully reveals how the D atom dynamically approaches CH₄ at different total angular momenta or impact parameters. This discovery of the reporter mode provides an opportunity for the detailed study of polyatomic reaction dynamics.