The A ( r, γ ) and B ( r, γ ) coefficients are obtained in a way similar to the one described above, considering the first two values of the ab initio potential energy V ( R = 2 a.u.; r, γ ) and V ( R = 2 . 052 a.u. ; r, γ ), and are further interpolated for any ( r , γ ) using the same 2D B-spline procedure. FIG. 2: Energy contour plots of the H − 3 electronic ground state PES in the space of the two internuclear distances ( r$_{1}$ and r$_{2}$ ) for two values of the bonding angle δ defined in each plot. Successive contours differ by 0 . 006 a.u. The dissociation energy D$_{as}$ = − 1 . 7016828 a.u. of the PES corresponds to the infinite separation between H$_{2}$( r$_{e}$ =1.403 a.u.) and H − (see Table I). The energy minimum (indicated by M ) is obtained for a linear configuration, and the top of the potential barrier is labeled with B . The lowest contour corresponds to the energy of − 1 . 7034 a.u. (left plot) and − 1 . 6974 a.u. (right plot). We show in Fig. 2 the H − 3 PES as a function of two internuclear distances, r$_{1}$ and r$_{2}$ for two values (180 and 90 ° ) of the bonding angle δ . These coordinates are convenient to describe main features of the PES. As expected, the figure is symmetric with respect to the r$_{1}$ ↔ r$_{2}$ exchange, and shows the van der Waals potential well in each coordinate (with the minimum labeled with M ), separated by a potential barrier (with the maximum labeled with B ) for the exchange of two identical nuclei. As in previous studies, lowest energy is found for a linear configuration. The position and energy of M and B are reported in Table I, together with other characteristic parameters of the PES. The Fortran subroutines calculating the PES and PDMS from the present ab initio data 7