Interaction energy along R of the C₃ + H₂ complex. Panel A: energies computed using the four-dimensional PES (solid lines) and from ab initio calculations (points) at several angular configuration (θ₁, θ₂, φ) of C₃ and H₂ that are notincluded in the grid used for the fit. Panel B: energies computed from the PES (solid lines) and analytical multipolar expansion (dashed line) at several angular configuration.