The H 2 Cl + potential energy surface (PES), V(Q), was obtained by fitting 145 ab initio points at CCSD(T)-F12b/VTZ-F12 level using symmetrized coordinate displacements (θθ eq , 1/2(R 1 + R 2 ) -R eq and 1/2(R 1 -R 2 )). Along these displacements, the grid ranges in bohr are [-0.90 : 1.03], [-0.41 : 0.65] and [0.00 : 0.48], respectively. The full grid covers energies up to about 10000 cm -1 and it has been fitted as linear combinations of coordinate displacement products. The fitted potential reproduces almost perfectly the ab initio points. Indeed, the root-mean-square error and the maximum error are about 0.1 cm -1 and 0.5 cm -1 , respectively. Furthermore, Fig. shows the ab initio energy points (red crosses) and the fitted potential (solid blue line) along the three symmetrized coordinates (θ, R + and R -), which clearly shows the almost perfect agreement.