Find the matrix $A$ of the reflection in the line $L$ in ${\mathbb R} ^2$ that consists of all scalar multiples of the vector $\left[\begin{array}{c} 2\cr 3 \end{array}\right] .$

$A=$ $\left[\Rule{0pt}{2.4em}{0pt}\right.$$\left]\Rule{0pt}{2.4em}{0pt}\right.$