The slope of the tangent to a curve $C: y=y(x)$ at any point $[x, y)$ on it is $\frac{2 e^{2 x}-6 e^{-x}+9}{2+9 e^{-2 x}}$. If $C$ passes through the points $\left(0, \frac{1}{2}+\frac{\pi}{2 \sqrt{2}}\right)$ and $\left(\alpha, \frac{1}{2} \mathrm{e}^{2 \alpha}\right)$ then $\mathrm{e}^\alpha$ is equal to :