So, I am trying to work in Spherical coordinates. I have a predefined fixed axis, $\hat{v}_0$, so that $\alpha=\vec{r}.\hat{v}_0$ Now, I am interested in the following: \begin{equation} f(r,\alpha)=\partial_{i}\partial_{j}\frac{\partial^2}{\partial^2 \alpha}\frac{\sin(kr)}{r}. \end{equation}
How do I find $f(r,\alpha)$? I have no clue how to proceed?