# Hydrogen wave function in momentum space

We can seperate the wave function of an hydrogen atom in a radial and an angle part: $$\phi_{n,l,m} (\mathbf{r}) = R_{n,l,m}(r) Y_{l,m}(\vartheta,\varphi) \, ,$$ where $Y_{l,m}$ are the spherical harmonics.
My question is: How does this look like in momentum space? Is the general form preserved? Do we get as well a radial and an angle dependent part?

## 1 Answer

To get it in the momentum representation, one has to do the Fourier transform of this function. This reference can be useful:

http://forum.sci.ccny.cuny.edu/Members/lombardi/publications/MOMREP-H-atom.pdf/view

At the end, separation of variables after transformation to the momentum space is not trivial, and the mixing of quantum number is presented.

• I am not convinced. The Fourier transform contains $\exp (- \mathrm{i} \mathbf{k} \cdot \mathbf{r})$ which mixes the integration of the angles and the radius.
– DaP
Commented May 2, 2013 at 8:45
• I think the momentum operator should not be necessary in Cartesian coordinates. I added a reference relating to your question. Commented May 2, 2013 at 8:53
• Ok, so the 'forminvariance' is a consequence of the Hamiltonian in the Schrödinger equation. I guess it is not easy (and though not a good idea) to show this using a Fourier transformation.
– DaP
Commented May 2, 2013 at 9:07
• Yes, I guess you are right. Now I see from that paper, that separation of variables is a bit tricky since the mixing of quantum numbers is presented. Commented May 2, 2013 at 9:10