2. Given the hyperbola $C_{1}: 2 x^{2}-y^{2}=1$, and the ellipse $C_{2}$ : $4 x^{2}+y^{2}=1$. If $M$ and $N$ are moving points on the hyperbola $C_{1}$ and the ellipse $C_{2}$ respectively, $O$ is the origin, and $O M \perp O N$, then the distance from point $O$ to the line $M N$ is $\qquad$