The tensor operator in the nucleon-nucleon potential is given by $$ \begin{array}{ll} &\\ \langle lSJ\vert S_{12}\vert l'S'J\rangle =& (-)^{S+J}\sqrt{30(2l+1)(2l'+1)(2S+1)(2S'+1)}\\ &\times\left\{\begin{array}{ccc}J&S'&l'\\2&l&S\end{array}\right\} \left(\begin{array}{ccc}l'&2&l\\0&0&0\end{array}\right) \left\{\begin{array}{ccc}s_{1}&s_{2}&S\\s_{3}&s_{4}&S'\\ 1&1&2\end{array} \right\}\\ &\times\langle s_{1}\vert\vert \sigma_{1}\vert\vert s_{3}\rangle \langle s_{2}\vert\vert \sigma_{2}\vert \vert s_{4}\rangle, \end{array} $$ and it is zero for the \( ^1S_0 \) wave.

How do we get here?