Seemingly Anomalous Angular Distributions in H + D 2 Reactive Scattering

Abstract

Spinning Backwards When atoms and molecules collide, the energy embedded in the reaction products gets distributed among translations, vibrations, and rotations. Decades of meticulous experiments have mapped out the quantum mechanical rules underlying this distribution process, particularly in simple systems comprising just three light atoms. Now, Jankunas et al. (p. 1687 ; see the Perspective by Yang et al. ) describe a previously unappreciated wrinkle in the elementary reaction of an H atom with deuterium. Typically, products with low vibrational and rotational excitation tend to scatter backwards from the collision, whereas the spinning products scatter sideways. Above a certain vibrational threshold, however, spinning HD products were observed to scatter backwards.