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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

4

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

6

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