r-dependent strong field ionization from a neutral ground state diatomic molecule g. n. gibson, h....
TRANSCRIPT
R-dependent strong R-dependent strong field ionization from a field ionization from a neutral ground state neutral ground state diatomic moleculediatomic molecule
G. N. Gibson, H. Chen*, V. G. N. Gibson, H. Chen*, V. Tagliamonti*Tagliamonti*
University of ConnecticutUniversity of Connecticut
*Also giving talks in this session*Also giving talks in this session
DAMOP 2012Anaheim, CAJune 6, 2012
Funding from the National Science
Foundation
R-dependent R-dependent ionizationionization
• Important test of any strong-field theory of ionization• Simple tunneling models do not agree with
experiments on Iodine• Rcritical in even charged molecules?• Lochfrass – implies very strong dependence of
ionization rate on R near Re: Γ(R)
• » Want to measure Γ(R) directly from the ground state over a large range in R – should see a huge effect
• Chen: ionization from the B-state vs. R• Tagliamonti: 1ω2ω ionization from the B-state vs.
RDAMOP 2012 2
Pump-dump-probePump-dump-probe
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4 5 6 7 8 9 10 11 120
1
2
3
10
12
14
16
18
0
5
10
15
20
25
31.0
31.5
32.0
(2,0)u
(2,1)
B u
+
I2
I+
2
R (a.u.)
I2+ 2 p
oten
tial
ene
rgy
(eV
)
X g,3/2
(1,1)
(2,0)g
I2+
2
X g
+
A u,3/2
I 2, I+ 2 p
oten
tial
ene
rgy
(eV
)
Not to scale
Pum
p
Pro
be
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Depletion at 45 fsDepletion at 45 fs
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.00
0.02
0.04
0.06
(2,1
) S
igna
l
3600
3650
3700
3750
3800
3850
3900
Delay [ps]
TO
F [
ns]
(2,1)
(2,1)
(2,0)
Depletion of B-state into X-state
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Wavepacket monitored Wavepacket monitored in (2,0) channelin (2,0) channel
(20% excitation)*(75% de-excitation) = 15% in high-v X-stateDAMOP 2012 6
Fourier Transform Fourier Transform SpectroscopySpectroscopy
0 2 4 6 8 10 12 14 16 18 20 22 243600
3650
3700
3750
3800
3850
3900
Frequency [ps-1]
TO
F [
ns]
X-state v=0"Lochfrass"
X-state v= 33!Returning wavepacket
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What about IWhat about I22++ signal? signal?
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What happened to What happened to expected modulation?expected modulation?
• NO modulation at 5 THz in the I2+ signal
• However, we do see strong 6.3 THz modulation – this is due to Lochfrass in the ground state near Re
• We know that Γ(R) must be a strongly increasing function of R, because of Lochfrass, which should lead to a huge modulation of the ionization rate, because the range of R is much bigger.
• However, Lochfrass does not give the final state, only the rate out of the ground state Γtotal(R) = Γ→X-state(R) + Γ→(1,0)(R)since (1,0) is the only other 1-e ionization signal.
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ΓΓ(R) has strong (R) has strong dependence, just not dependence, just not
to Ito I22++
• (1,0) represents ionization from an inner-orbital or into strongly mixed states.
• HOMO is antibonding - ionization won’t lead to (1,0).
• Inner orbitals are bonding – ionization will weaken bond.
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Branching ratio Branching ratio between Ibetween I22
++ and (1,0) and (1,0) channelschannels
• Even single pulse branching ratio to (1,0) is very large ~67%.
• Branching ratio increases with R, as measured from the B state.
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Orbital structureOrbital structure
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ConclusionsConclusions• Ionization projects ion into mixed states
o Asymmetric work of Tagliamontio Branching ratio to (1,0)o At large R, molecule falls apart
• Hard to claim we are cleanly removing an electron from one orbital of another – everything gets highly mixed by the field
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