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Dissipation and Coherence: Halogens in Rare Gas Solids. Signatures of Dissipation in Pump-Probe Spectra Dissipation of Energy in Excited Halogens Dispersion and „Decoherence“: Classical vs. Quantum Effects New Experiments with Phase-Locked Pulses. - PowerPoint PPT Presentation
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Dissipation and Coherence:Halogens in Rare Gas Solids
• Signatures of Dissipation in Pump-Probe Spectra
• Dissipation of Energy in Excited Halogens
• Dispersion and „Decoherence“: Classical vs. Quantum Effects
• New Experiments with Phase-Locked Pulses
M. Bargheer, M. Gühr, P. Dietrich, M. Fushitani, T. Kiljunen and N. Schwentner
Institut für Experimentalphysik
Diatomics in Solid Rare Gas
• I2 in Kr
• Fcc lattice, closest packing
• Adiabatic dynamics including dissipation are well described in classical simulations
• strong coupling to „solvent“
• some similarities to gas phase
P u m p = P ro b e = 4 9 0 nm 5 0 0 nm
E 0
R
t0ji
ji
tt
EE
d t
d E
R elaxation R ate :
0.0
0 .2
0 .4
0 .6
0 .8
1 .0
norm
.flu
ores
cenc
e
0 1 2 3 4
t / ps
Energy loss from oscillations
Bargheer et al., PCCP 4, 75 (2002)
Energy loss from signal envelope
probe =
480 nm
490 nm
500 nm
510 nm
520 nm
530 nm
540 nm
fluor
esce
nce
sign
al/a
.u.
pum p = 500 nm
m
E
E0
t0 t
Sig
nal
ji
ji
tt
EE
d t
d E
R elaxation R ate :
Vibrational relaxation ofI2/Kr
-3000 -2000 -1000 0 10001
10
100
1000
10000
-3000 0 3000 6000
1
10
100
1000
10000
dE
/dt
/ cm
-1/p
s
Eexcess
/ cm-1
dissociation limit
dissociation limit
dE
/dt / cm
-1/ps
Eexcess
/ cm-1
I2/Kr
Vibrational relaxation ofI2/Kr, ClF/Ar and Cl2/Ar
-3000 -2000 -1000 0 10001
10
100
1000
10000
-3000 0 3000 6000
1
10
100
1000
10000
and ClF/Ar 100 % loss in one collision for I
2/Kr
dE
/dt
/ cm
-1/p
s
Eexcess
/ cm-1
dissociation limit
dissociation limit
dE
/dt / cm
-1/ps
Eexcess
/ cm-1
I2/Kr
ClF/Ar Cl
2/Ar
Collisions Cause Coherence?
0 1 2
LIF
/ a.
u.
t / ps
Collision of I2 with surrounding Kr
•Width of wavepacket: 500 cm-1
•Energy loss in collision: 1500 cm -1
•Collision populates new vibrational levels coherently!
• well defined timining of collision
• well defined scattering geometry!
R
E 0
Mechanisms of „Dephasing“
• Decoherence due to collisions with solvent (pure dephasing T2´)
• Population decay by vibrational relaxation (and non-adiabatic couplings) (relaxation time T1)
• Dispersion due to anharmonicity (dispersion time Tdisp)
0.0 0.5 1.0 1.5 2.0
E = 600 cm-1
E = 200 cm-1
E = 50 cm-1
Ove
rlap
with
pro
be w
indo
w
t / psR
Ene
rgy
Dispersion: Classical and Quantum Effects
• Compensation of dispersion by negative chirp of excitation pulse
• Classical!
0 5 10 15 20
calc
. sig
nal
t / ps
• Rephasing of wavepacket after dispersion
• Rephasing time Trep = 1/exe
(after dispersion of the packet)
• discrete vibrational levels needed
0 1 2 3 4
calc
. sig
nal
t / ps
Dispersion in Morse-Potential (Classical)
•Morse-potential:
•Frequency:
200 exp1)( rrDrV
01 DE
emorse
eexm 2
R
ExTee
morsedisp
2
T1
T2
T = n(T1 - T2)
•Dispersion-time:(wave packet width T > 1/2Tmorse)
Ene
rgy
Dispersion of I2-Wave-Packets
17.5 18.0 18.5 19.0 19.5 20.00.0
0.2
0.4
0.6
0.8
1.0
1.2
570 560 550 540 530 520 510 500
FWHM = 785 cm-1 (10 states)
FWHM = 285 cm-1 ( 4 states)
VibrationalLevels
sign
al /
a.u
.
excitation pulse / 1000 cm-1
[nm]
Tdisp= 2 ps
Tdisp= 5 ps
0 1 2 3 4 50.0
0.2
0.4
0.6
0.8
1.0
sim
ula
ted
sig
na
l
t / ps
10 states 4 states
0.0
0.2
0.4
0.6
0.8
1.0
1.2
me
asu
red
sig
na
l FWHM = 785 cm-1 (10 states)
FWHM = 285 cm-1 ( 4 states)
eeee
morsedisp xNExT
2
12
If N = number of excited vibrational levels:
Dispersion of ClF-Wave-Packets
Tdisp< 1 pseeee
morsedisp xNExT
2
12
3 4 5 6 7
Ene
rgy
/cm
-1
R / a0
C l F+ -
B 30
0 1 2 3
Ar3
t / ps
Experiments with Phase-Locked Pulses
Generation of Pulse-Pairs: ConstructiveInterference
DestructiveInterference
Scherer et al., J. Chem. Phys. 95, 1487 (1991)
Piezo
Piezo tunes phase by movingdistance /2
Explanation in Frequency Domain
• Pulse-Pairs in frequency domain yield spectral interferences, if pulses overlap.• Frequency resolution of monochromator broadens pulses.
freq u en c y
inte
nsit
y
• Observed signal: Fluorescence, i.e. integrate from -∞ to +∞• Vibrational states act as a monochromator => interference
constructivedestructive
nointerference
Phase-Locked Pulses in the Presence of Dissipation: Proposed Experiment: Cl2 in Ar
• Phonon side-bands increase for higher vibrational levels• Excitation of zero-phonon lines => oscillation of free molecule?
Cl2 / Ar
• Excitation of phonon sidebands => dissipative dynamics
• Coherent control of dissipative vs. free wave packet motion
constructivedestructive
nointerference
Summary
R
E 0
-3000 -2000 -1000 0 10001
10
100
1000
10000
-3000 0 3000 6000
1
10
100
1000
10000
and ClF/Ar 100 % loss in one collision for I
2/Kr
dE
/dt
/ cm
-1/p
s
Eexcess
/ cm-1
dissociation limit
dissociation limit
dE
/dt / cm
-1/ps
Eexcess
/ cm-1
I2/Kr
ClF/Ar Cl
2/Ar
• Signatures of relaxation
• Energy loss of halogens in Rg
•Collisions cause coherence
• Dispersion in anharmonic potentials
• Experiments with phase-locked pulse pairs
0 1 2 3 4 50.00.2
0.40.6
0.81.0
sim
ulat
ed s
igna
lt / ps
10 states 4 states