Calculate Spin-Orbit Coupling in 19K: Estimate <(1/r)dV/dr>

[andyfreesty1e]

Homework Statement

The 4p → 4s transition in 19K produces a pair of lines at 766.49nm and 769.90nm.
Estimate the value of <(1/r)dV/dr> for the optically active electron in 19 K

Homework Equations

The Attempt at a Solution

help needed urgently please. All i know so far is E=hc/(lamda) so therefore
dE=hc/(lamda)^2 d(lamda)

 

[vela]

How does the spin-orbit interaction affect the energies of the 4s and 4p states? How is <(1/r)dV/dr> related to the spin-orbit interaction? Start there.