FIGURE 1. Three-dimensional product contour plots as a function of product velocity.

Shown are product contour plots versus product velocity in the centre-of-mass frame obtained experimentally (a) and theoretically (b). Experimentally, time-of-flight spectra of the D-atom product were measured at every 5 degrees and then converted into the translational energy distribution in the centre-of-mass frame. From these translational energy distributions, the angular distributions of all H₂-product quantum states can be determined. The experimental 3D product contour plot (a) is obtained from fitting smoothly the experimental angular distributions of all product (H₂) quantum states using a multi-order polynomial function. Theoretically, the S-matrix for H + HD was calculated using quantum-reactive scattering methods described previously^17,18, on the BKMP2 PES²⁰. Differential cross-sections (DCS) at different centre-of-mass angles were computed from the S-matrix. The theoretical 3D product contour plot is constructed from these calculated DCS. The forward-scattering direction ( = 0°) is denoted F and the backward-scattering direction is denoted B. The height of the peaks represents the magnitude of DCS, while the radius from the centre represents the product translational energy, E_T.