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17.   Spectral Lines: Selection Rules, Intensities, Transition Probabilities, Values, and Line Strengths


Selection rules for discrete transitions
  Electric dipole (E1)
("allowed")
Magnetic dipole (M1)
("forbidden")
Electric quadrupole (E2)
("forbidden")

Rigorous rules   1.   Δ J = 0, 1
(except 0 is not allowed 0)
Δ J = 0, 1
(except 0 is not allowed 0)
Δ J = 0, 1, 2
(except 0 is not allowed 0,
1/2 is not allowed 1/2, 0 is not allowed 1)

  2. ΔM = 0, 1
(except 0 is not allowed 0
when Δ J = 0)
ΔM = 0, 1
(except 0 is not allowed 0
when Δ J = 0)

ΔM = 0, 1, 2
  3. Parity change No parity change No parity change

With negligible
configuration
interaction
4. One electron
jumping, with
Δl = 1,
Δn arbitrary
No change in electron
configuration; i.e., for
all electrons, Δl = 0,
Δn = 0
No change in electron
configuration; or one
electron jumping with
Δl = 0, 2, Δn arbitrary

For LS
coupling only
5. ΔS = 0 ΔS = 0 ΔS = 0
  6. ΔL = 0, 1
(except 0 is not allowed 0)
ΔL = 0
Δ J = 1
ΔL = 0, 1, 2
(except 0 is not allowed 0, 0 is not allowed 1)


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