In the absence of any spin-orbit coupling the bound eigenstates of the single-electron hydrogen atom are denoted by In, 1, m, m.). They have energy En = -R/n² where R is the Rydberg constant. You will consider the effect of including a spin-orbit interaction Ĥspin-orbit = BL-S, which we will treat as a perturbation. Here 3 is a real parameter, Ĺ is the operator corresponding to orbital angular momentum of the electron, and S is its spin operator. a) Before the spin-orbit interaction is switched on, what is the degeneracy of the n = 2 energy level? List the possible states using the notation In, l, mi, m.). b) Once the spin-orbit interaction is switched on, the degeneracy of the En level is partially lifted and 1, my, and m, are no longer "good" quan- tum numbers (i.e. they are no longer the eigenvalues of operators that commute with the Hamiltonian). What is a new set of good quantum numbers? c) Consider the perturbed eigenstates that arise from the n = 2, 1 = 1 states. Compute, to first order in 3, the shift in the energies from En=2. How many distinct energies are there after the perturbation, and what is the degeneracy of each? d) For the energy level with the highest degeneracy, write down all the perturbed eigenstates as explicit linear combinations of the original n = 2, 1 = 1 basis states (2, 1, m, m.). Hint: Ĵ² = (L+S)² = 1² + S² + 2L.Ŝ. Some possibly useful Clebsch-Gordan coefficients (ji, m₁; j2, m2|jtot, mtot): (1, m,, mot) = mot 3 (1, m,,mtot) = ± #V mtot 3

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In the absence of any spin-orbit coupling the bound eigenstates
of the single-electron hydrogen atom are denoted by In, l, m, m.). They have
energy En-R/n² where R is the Rydberg constant. You will consider the
effect of including a spin-orbit interaction
which we will treat as a perturbation. Here is a real parameter, Ĺ is the
operator corresponding to orbital angular momentum of the electron, and S
is its spin operator.
a) Before the spin-orbit interaction is switched on, what is the degeneracy
of the n = 2 energy level? List the possible states using the notation
In, l, mi, m.).
Ĥsp
spin-orbit = BL-S,
b) Once the spin-orbit interaction is switched on, the degeneracy of the
En level is partially lifted and I, my, and m, are no longer "good" quan-
tum numbers (i.e. they are no longer the eigenvalues of operators that
commute with the Hamiltonian). What is a new set of good quantum
numbers?
c) Consider the perturbed eigenstates that arise from the n = 2, 1 = 1
states. Compute, to first order in 3, the shift in the energies from En-2.
How many distinct energies are there after the perturbation, and what
is the degeneracy of each?
d) For the energy level with the highest degeneracy, write down all the
perturbed eigenstates as explicit linear combinations of the original
n = 2, 1 = 1 basis states [2, 1, m, m.).
Hint:
Ĵ² = (Î + Ŝ)² = Ĺ² + Ŝ² + 2 η Ŝ.
Some possibly useful Clebsch-Gordan coefficients (ji, m₁; j2, m2|jtot, mtot):
(1,m₁; ,, mtot) =
± Mtot
3
(1, m,, mtot) = ±
√
FMtot
Transcribed Image Text:In the absence of any spin-orbit coupling the bound eigenstates of the single-electron hydrogen atom are denoted by In, l, m, m.). They have energy En-R/n² where R is the Rydberg constant. You will consider the effect of including a spin-orbit interaction which we will treat as a perturbation. Here is a real parameter, Ĺ is the operator corresponding to orbital angular momentum of the electron, and S is its spin operator. a) Before the spin-orbit interaction is switched on, what is the degeneracy of the n = 2 energy level? List the possible states using the notation In, l, mi, m.). Ĥsp spin-orbit = BL-S, b) Once the spin-orbit interaction is switched on, the degeneracy of the En level is partially lifted and I, my, and m, are no longer "good" quan- tum numbers (i.e. they are no longer the eigenvalues of operators that commute with the Hamiltonian). What is a new set of good quantum numbers? c) Consider the perturbed eigenstates that arise from the n = 2, 1 = 1 states. Compute, to first order in 3, the shift in the energies from En-2. How many distinct energies are there after the perturbation, and what is the degeneracy of each? d) For the energy level with the highest degeneracy, write down all the perturbed eigenstates as explicit linear combinations of the original n = 2, 1 = 1 basis states [2, 1, m, m.). Hint: Ĵ² = (Î + Ŝ)² = Ĺ² + Ŝ² + 2 η Ŝ. Some possibly useful Clebsch-Gordan coefficients (ji, m₁; j2, m2|jtot, mtot): (1,m₁; ,, mtot) = ± Mtot 3 (1, m,, mtot) = ± √ FMtot
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