Selective Cascade feeding of metastable states In IonAtom Collisions - PowerPoint PPT Presentation

Title: Selective Cascade feeding of metastable states In IonAtom Collisions


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Selective Cascade feeding of metastable states
In Ion-Atom Collisions
Theo J.M. Zouros Dept. of Physics, University of
Crete, Heraklion Institute of Electronic
Structure Laser, Heraklion Crete, GREECE
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References
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Early history
4P - Pure TL no spin flip allowed
Sharp drop in cross-section with increasing
projectile energy reminiscent of capture
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Electron-electron Excitation (eeE)
TL
Puzzle R. Shingal coupled channel TL
Calculation of O5 H about 100 times too
small!!!
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Auger transition Selection rules
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O5 (1s2s2p 4PJ)Atomic structure
prompt
-1173 eV 1s2s2p 1P 2P3/2.1/2
t14.4 fs
t158 fs
-1186 eV 1s2s2p 3P 2P3/2,1/2
Auger branching ratios
99.6
Spin-orbit mixing
metastable
73.9
-1195 eV 1s2s2p 4P5/2,3/2,1/2
t27.7 ns
J5/2
t0.91 ns
J1/2
96.7
t3.34 ns
J3/2
Auger branching ratios
70.1
99.98
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New TL Independent Particle Model calculations

• 2p Transfer computed by CDW
• 1s Loss computed by SCA
• LS-coupling Auger angular distribution
• Average over H-H orientations

Some improvement but H2 data Still off by a
factor of 10!
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New nTL calculations

• CDW calculation for capture
• to O5(1s2s 3S)nl probability
• for n2 rather than just n2
• Substantial capture to ngt2 observed! Same for
  F6.
• CTMC and CDW agree

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CDW TL results Zouros et al
JPBL 2006
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AddRadiative Cascade feedingof 1s2s2p 4Pofrom
higher lying prompt 1s2snl 4Lo statesformed by
nTL
Yrast line cascade feeding
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Zouros et al JPBL 2006
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Summary

• New TL calculations for the production of the
  long-lived
• 1s2s2p 4P state have been performed in the IPM
  within
• a factor of 2 of existing data for O5 and
  almost in
• agreement for F6

• New idea (old idea) the inclusion of cascade
  feeding
• from higher lying 1s2snl 4L states also
  produced by TL

• Since cascade feeding rates and branching ratios
  are
• still unknown we have assumed that ALL 1s2snl
  4L states
• produced are eventually converted to 1s2s2p 4P
  states
• thus establishing an upper limit for this
  contribution

• Whether yet another mechanism is needed to
  account for
• the missing factor of 2 remains an interesting
  possibility

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Ratio of 4P to 2P in single electron capture
From pure spin statistics R2
Tanis et al PRL2004
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Pauli exchange interaction
1s2s 3S

• An electron with antialigned spin
• can populate either the 1s, 2s or
• 2p levels, in the later case giving
• rise to the 2P state

• An electron with a spin aligned
• with the spin of the 1s projectile
• electron cannot be captured into
• the 1s due to Pauli blocking
• so instead it gets promoted up
• into the 4P state adding to
• direct 2p capture!

Tanis et al PRL2004
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Differential cascade feeding - 5-level example
with n3
1s2s3l quartet states are blocked from Cascading
to 1s22s ground state
1s2s3l doublet states are readily depleted
by Cascading to 1s22s ground state
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Differential cascade feeding - 5-level example
with n3

• 1s2s2p 4P should get more cascade feeding than
  1s2s2p 2P
  since there is less lost to other
  channels!
• Ratio of 1s2s2p 4P / 1s2s2p 2P should be
  relatively enhanced (Comment to PRL 2005)

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Summary

• CDW and CTMC calculations show that single
  electron
• capture to 1s2s 3S ionic states can form
  higher-lying
• 1s2snl 2L doublets and 1s2snl 4L quartet
  states with n2-7
• in relatively high numbers even in 1-2 MeV/u
  collisions

• 1s2snl 2L states can dipole decay strongly
  feeding lower
• lying doublet levels eventually cascading all
  the way down
• to the 1s22s 2S ground state.

• 1s2snl 4L states can also dipole decay but only
  to quartets
• Thus for them the lowest ground state is the
  1s2s2p 4P state.

• This results in the strong enhancement of the
  1s2s2p 4P states
• relative to the 1s2s2p 2P states and thus to a
  mechanism for
• selective cascade feeding.

• This explanation resolves the 4P TL puzzle and
  provides a
• less speculative mechanism for enhancing
  R4P/(2P2P-)

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The end
Thanks for listening!