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Pressure broadening

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The presence of pertubing particles near an emitting atom will cause a broadening and possible shift of the emitted radiation.

There is two types impact and quasistatic

In each case you need the profile, represented by Cp as in C6 for Lennard-Jones potential

Assume Maxwell-Boltzmann distribution for both cases.

Impact broadening

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From (Peach 1981, p. 387)

For impact, its always Lorentzian profile

  • Linear Stark p=2
Broadening by linear Stark effect
Debye effects must be accounted for
  • Resonance p=3
Broadening by ???
  • Quadratic Stark p=4
Broadening by quadratic Stark effect
  • Van der Waals p=6
Broadening by Van der Waals forces

Quasistatic broadening

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From (Peach 1981, p. 408)

For quasistatic, functional form of lineshape varies. Generally its a Levy skew alpha-stable distribution (Peach, page 408)

  • Linear Stark p=2
Broadening by linear Stark effect
  • Resonance p=3

where K is of order unity. Its just an approximation.

  • Quadratic Stark p=4
Broadening by quadratic Stark effect
(Peach1981 & Peach 1981, Eq 4.95)

where and are the static dipole polarizabilities of the i and j energy levels.

  • Van der Waals p=6
Broadening by Van der Waals forces gives a Van der Waals profile. C6 is the wing term in the Lennard-Jones potential.

for

0 otherwise.

(Peach 1981, Eq 4.101)
(Peach 1981, Eq 4.100)

where K is of order 1.