\lambda_1 \\ 0 & 0 & 0 \end{array} \right)
\left( \begin{array}{ccc} j_2 & j'_2 & \lambda_2 \\ 0 & 0 & 0 \end{array} \right)
\left( \begin{array}{ccc} l & l' & \lambda_{12} \\ 0 & 0 & 0 \end{array} \right) \\
\left\{ \begin{array}{ccc} l & l' & \lambda_{12} \\ j'_{12} & j_{12} & J \end{array} \right\}
\left\{ \begin{array}{ccc} j'_{12} & j'_2 & j'_1 
\\ j_{12} & j_2 & j_1 \\ \lambda_{12} & \lambda_2 & \lambda_1  \end{array} \right\}, \end{gathered}$$ with the notation $$\begin{aligned}
[x_1, x_2, ... , x_n] = (2x_1+1) (2x_2+1) ... (2x_n+1).\end{aligned}$$

For two indistinguishable molecules, one has to symmetrize the wave function with respect to the exchange-permutation symmetry of the molecules. Under molecule permutation $P$, $P \phi^{JM\varepsilon_I}_{vjl} = (-1)^{j_1+j_2+j_{12}+l} \phi^{JM\varepsilon_I}_{\bar{v}\bar{j}l}$, where $\bar{v} \equiv v_2v_1$ and $\bar{j} \equiv j_2j_1j_{12}$. As a consequence, properly symmetrized exchange-permutation invariant states must be employed for the basis set, $$\begin{gathered}
\phi^{JM\varepsilon_I\varepsilon_P}_{vjl}(\vec{r}_1,\vec{r}_2,\hat{R}) = \\
\Delta_{vj_1j_2} 
\left[ \phi^{JM\varepsilon_I}_{vjl}
+ \varepsilon_P (-1)^{j_1+j_2+j_{12}+l} 
\phi^{JM\varepsilon_I}_{\bar{v}\bar{j}l} \right] ,\end{gathered}$$ with $\varepsilon_P = \pm 1$, $\Delta_{vj_1j_2}=[2(1+\delta_{v_1v_2}\delta_{j_1j_2})]^{-1/2}$, and $$\begin{aligned}
P \phi^{JM\varepsilon_I\varepsilon_P}_{vjl} = \varepsilon_P \phi^{JM\varepsilon_I\varepsilon_P}_{vjl}. \end{aligned}$$ The total wavefunction is expanded as $$\begin{gathered}
\Psi(\vec{r}_1,\vec{r}_2,\vec{R}) = \\
\frac{1}{R}
\sum_{v,j,l,J,M}^{*} F_{vjl}^{JM\varepsilon_I\varepsilon_P}(R) 
\phi^{JM\varepsilon_I\varepsilon_P}_{vjl}(\vec{r}_1,\vec{r}_2,\hat{R}),\end{gathered}$$ where the superscript over the sum symbol indicates a summation over states that have to follow 