- #1
snatchingthepi
- 148
- 38
Homework Statement
Starting from
[tex]E^1_{fs} = \left<n l m_l m_s| (H_r + H_{so})| n l m_l m_s \right>[/tex]
and using
[tex]E_r^1 = -\frac{(E_n)^2}{2mc^2}\left[\frac{4n}{l+1/2} - 3\right][/tex]
and
[tex]H_{so} = \frac{e^2}{8\pi\epsilon_0}\frac{S\cdot L}{m^2c^2r^3}[/tex]
and
[tex]\left<\frac{1}{r^3}\right> = \frac{1}{l(l+1/2)(l+1)n^3a^3}[/tex]
where 'a' is the Bohr radius,
and
[tex]\left<S \cdot L\right> = \left<S_x\right>\left<L_x\right> + \left<S_y\right>\left<L_y\right> + \left<S_z\right>\left<L_z\right>[/tex][/B]
derive
[tex]E_{fs}^1 = \frac{13.6}{n^3}\alpha^2\left[\frac{3}{4n} - \left(\frac{l(l+1) - m_lm_s}{l(l+1/2)(l+1}\right)\right] [/tex]
Homework Equations
As above.[/B]
The Attempt at a Solution
The first bit of this is extremely straight-forward. I substitute the appropriate values and use the S.L stuff above to get
[tex]E^1_{fs} = \left<n l m_l m_s| (H_r + H_{so})| n l m_l m_s \right> = \frac{-(E_n)^2}{2mc^2}\left[\frac{4n}{l+l/2} - 3\right] + \frac{e^2}{8\pi\epsilon_0}\frac{\hbar^2m_lm_s}{m^2c^2}\frac{1}{l(l+1/2)(l+1)n^3a^3}[/tex]
but from here on I seem to run into a stumbling block. I just don't how to get out any value of 13.6 [eV]. I know I can reexpress
[tex]E_n = \frac{-\alpha^2mc^2}{2n^2} = \frac{-m}{2n^2}\left(\frac{e^2}{4\pi\epsilon_0\hbar}\right)^2[/tex]
but I am not seeing how to move forward. Trying to use this on the the E_n term in the RH of the above I get
[tex]\frac{\alpha^4mc^2}{8n^4}[/tex]
which seems to get me nowhere.
Could someone give me a kick in the right direction? I'm not seeing where to go with all this mathturbation.[/B]