photochemistry and vibrational dynamics of glycolaldehyde in cryogenic matrices. team: claudine...
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Photochemistry and vibrational dynamics of glycolaldehyde in cryogenic matrices.
Team: Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien Daquin, Michel Broquier.
Raphaël THONDoctorant deuxième année
Journées de l’EDOM 7 et 8 Mars 2011
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Atmospheric interestAstrophysic interestSugar model CnH2nOn
Fundamental studies. (Hydrogen bond) Frozen molecules in the ground states
(simplified spectra)High quantitiesEnvironment effects
Glycolaldehyde in cryogenic cristalline matrix.Why?
C2H4O2
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Photochemistry: ultraviolet irradiation
Infrared diagnostic
Glycoladehyde in Argon matrix (T=10K)
UV irradiation by excimer laser emitting at 193nm or
248 nm.
Gas phase:Different dissociation pathways
• Isomerisation
HOCH2CHO
( Cc )HOCH2CHO
( Tt )
+ hν
HOCH2CHO(Cc)
+ hν CO
+CH3OH
Matrix: products of irradiation
•Fragmentation
1000 1020 1040 1060 1080 1100 1120
Abs
orb
ance
Wavenumber, cm-1
0
15
45
135
CC
Tt Tt CH3OH
2120 2160
CO
2140
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Photochemistry: kinetics λ=193 nm
All fragments appears at the same timeCorrelation between Cc disappearance and Tt formation (5’)Open geometry only present in matrix
0 50 100 150 200 250 3000,00
0,04
0,08
0,12In
tens
ity
Time (minutes)
Results differ from gas phase. Toward the comprehension of mechanisms
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Vibrational dynamics probed by photon echoMotivations:
•Influence of environment on vibrational modes•Coupling between vibrational modes
Method: photon echo produced by degenerate four wave mixing
Non linear spectroscopy to separate the two contributions.
Homogeneous broadening: hom
Inhomogeneous broadening: inhom
Dephasing time
Population relaxation time
Pure dephasingtime
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T
focalisationsample
Detection
k2
k1
t
t=-T-τ
k3
ks = - k1+ k2 k3
t=0 t=-T
ks
k1
k2
k3
Photon Echo: principle
Detected signal
And:
Scanning of τ: measure of T2, the coherence time
Scanning of T: measure of T1, the population relaxation time
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Experimental set-up
Collaboration: Bernard Bourguignon, Aimeric Ouvrard
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Experimental steps
CCl4
Temporal superposition. Detection of interferences when pulses overlap.
-0,4 -0,2 0,0 0,2 0,4-1000
-800
-600
-400
-200
0
inte
nsity
(a.
u)
time (ps)
interferences between k1 and k2 gaussian fit
FWHM=300 fs
Very high dipolar moment: 1D
Test on a tungsten hexacarbonyl W(CO)6
CO streching mode. ν = 1980 cm-1
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Preminilary results on W(CO)6
-2 -1 0 1 2 3 4 5 6200
400
600
800
1000
1200
inte
nsity
(a.
u)
delay (ps)
-100 0 100 200 300 400 500
200
400
600
800
1000
1200
1400
inte
nsity
(a.
u)
delay (ps)
T2=2 ps T1=620 ps
(in liquid )
What about glycolaldehyde in matrix?
… to be followed
CCl4
Tokmakoff and al. J.Chem Phys. 100 (12) 15 June 1994
Dephasing time Population relaxation time
T2=10 ps
-10 -5 0 5 10 15 20 25
200
400
600
800
1000
1200
Inte
nsity
(a.u
)
delay (ps)
T2 (matrix) > T2 (solution)
(in N2 matrix. T=22K)
Dephasing time
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Thank you for your attention.Merci pour votre attention.
Acknowledgments
Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien Daquin, Michel Broquier, Bernard Bourguignon, Aimeric Ouvrard, Julien Vincent
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First results on the test solution
-2 -1 0 1 2 3 4 5 6200
400
600
800
1000
1200
photon echo of W(CO)6
fit
inte
nsity
(a.
u)
delay (ps) Measure of the coherence time T2=2,57 ps
Fit by the following functfion:
(exponential decay convolved by the pulse shape)
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1000 1200 2200
-0,25
-0,20
900 1000 1100 1200 2050 2100 2150 2200 2250 2300 2350
-0,25
-0,20
900 1000 1100 1200 2050 2100 2150 2200 2250 2300 2350
-0,18
GA Tt GA Cc
optic
al d
ensi
ty
wavenumbers
0minuteGA Cc
Fragment CH3OHet CH3OH(CO)
optic
al d
ensi
ty
wavenumbers
5,5minutes
Fragments CO et CO(CH3OH)
Fragment CH3OHet CH3OH(CO)
Fragments CO et CO(CH3OH)
optic
al d
ensi
ty
wavenumbers
285minutes
Non identified band
Photochemistry: products of irradiation
D’après la Thèse d’Arnaud Cuisset, Dynamique vibrationnelle sondée par écho de photons de DCl et ses complexes piégés en matrices cryogéniques – Thèse Université Paris XI (2003)
Photon echo signal
r10 ∞ exp(-t/T2-iwt) exp(-t/T2+iwt)
3ème : diffraction : état de cohérence
exp(-T/Tg)
|1>
|0>
exp(-T/T1)
2nde : interférences réseau de populations
r11 ∞ exp(-t/T2-iwt) exp(-t/Tg)
r00 ∞ exp(-t/T2-iwt) exp(-t/T1) |1>
|0>
1ère impulsion : Etat de cohérencer00= ½0><0½ r01 ∞ exp(-t/T2-iwt)
|1>
|0>Rephasage à t=τ=> ECHO de photons
ks = - k1+ k2 k3
e-4t/ T2
S(t
)
0 t
Photon echo equations