@Alexander77]. For convenience we use the term “combined molecular state" (CMS), for a combination of two rovibrational states of two H$_2$ molecules. In this notation, H$_2(v_1,j_1)$ + H$_2(v_2,j_2)$ collisions will be denoted as $(v_1 j_1 v_2 j_2)$ and its energy is given by $\varepsilon_{vj} = \varepsilon_{v_1j_1} + \varepsilon_{v_2j_2}$. The CMS represents an unique quantum state of the diatom - diatom system before or after the collision. To gain physical insights into the scattering process and also to roughly estimate the number of CMSs to be included in the scattering calculations, we plot in Fig. \[SPAG-FIG\] the effective potentials which are composed of the diabatic energies and the centrifugal terms, $$\begin{aligned}
V_{\text{eff}}^{J}(R)=
\varepsilon_{vj} 
+ {\cal U}^{JM\varepsilon_I \varepsilon_P}_{vjl,vjl}(R)
+ \frac{\hbar^2 l(l+1)}{2 \mu R^2} ,
\label{DIABNRJ}\end{aligned}$$ as functions of the radial coordinate, $R$, evaluated using the BMKP PES. At large separations, the energies of the different potential curves converge to that of the corresponding CMSs as indicated by the numbers $(v_1 j_1 v_2 j_2)$ in Fig. \[SPAG-FIG\]. The energy of the CMS (0000) is 6270.73 K and that of (0200) is 6780.35 K. For the vibrationally excited case, (1000), the energy is 12257.57 K. The energy is relative to the minimum of the 