Journée de doctorants Raphaël THON Doctorant deuxième année 01/04/2017

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1 Journée de doctorants Raphaël THON Doctorant deuxième année 01/04/2017 Journées de l’EDOM 7 et 8 Mars 2011 Photochemistry and vibrational dynamics of glycolaldehyde in cryogenic matrices. Team: Claudine Crépin-Gilbert, Wutharath Chin, Jean-Pierre Galaup, Julien Daquin, Michel Broquier.

2 Glycolaldehyde in cryogenic cristalline matrix. Why?
Frozen molecules in the ground states (simplified spectra) High quantities Environment effects C2H4O2 Atmospheric interest Astrophysic interest Sugar model CnH2nOn Fundamental studies. (Hydrogen bond)

3 Photochemistry: ultraviolet irradiation
Gas phase: Different dissociation pathways Infrared diagnostic Glycoladehyde in Argon matrix (T=10K) UV irradiation by excimer laser emitting at 193nm or 248 nm. Isomerisation HOCH2CHO ( Cc ) ( Tt ) + hν  (Cc) CO + CH3OH Matrix: products of irradiation Fragmentation

4 Photochemistry: kinetics λ=193 nm
All fragments appears at the same time Correlation between Cc disappearance and Tt formation (5’) Open geometry only present in matrix Results differ from gas phase. Toward the comprehension of mechanisms

5 Vibrational dynamics probed by photon echo
Motivations: Influence of environment on vibrational modes Coupling between vibrational modes Method: photon echo produced by degenerate four wave mixing Homogeneous broadening: hom Inhomogeneous broadening: inhom  Non linear spectroscopy to separate the two contributions. Dephasing time Population relaxation time Pure dephasing time

6 Photon Echo: principle
 focalisation sample Detection k2 k1 t    t=-T-τ k3 ks = - k1 + k2 t=0 t=-T ks Detected signal And: Scanning of τ: measure of T2, the coherence time Scanning of T: measure of T1, the population relaxation time

7 Experimental set-up Collaboration: Bernard Bourguignon, Aimeric Ouvrard

8 Experimental steps Temporal superposition. Detection of interferences when pulses overlap. FWHM=300 fs Very high dipolar moment: 1D Test on a tungsten hexacarbonyl W(CO)6 CO streching mode. ν = 1980 cm-1 CCl4

9 Preminilary results on W(CO)6
Dephasing time Population relaxation time T1=620 ps T2=2 ps CCl4 (in liquid ) Tokmakoff and al. J.Chem Phys. 100 (12) 15 June 1994 T2=10 ps T2 (matrix) > T2 (solution) (in N2 matrix. T=22K) Dephasing time What about glycolaldehyde in matrix? … to be followed

10 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 Thank you for your attention. Merci pour votre attention.

11 First results on the test solution
Fit by the following functfion: (exponential decay convolved by the pulse shape) Measure of the coherence time T2=2,57 ps

12 Photochemistry: products of irradiation

13 Photon echo signal 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)

14 Photon echo equations 1ère impulsion : Etat de cohérence
ks = - k1 + k2 k3 1ère impulsion : Etat de cohérence r00= ½0><0½ r01 ∞ exp(-t/T2-iwt) |1> |0> Rephasage à t=τ => ECHO de photons 2nde : interférences  réseau de populations r11 ∞ exp(-t/T2-iwt) exp(-t/Tg) r00 ∞ exp(-t/T2-iwt) exp(-t/T1) |1> |0> e-4t/ T2 S(t) t r10 ∞ exp(-t/T2-iwt) exp(-t/T2+iwt) 3ème : diffraction : état de cohérence exp(-T/Tg) |1> |0> exp(-T/T1)