Thèse de doctorat en Physique
Sous la direction de Joëlle Rostas.
Soutenue en 1989
à Paris 11 .
Afin d'étudier les fragments produits par la photodissociation de l'eau, on dilue H2O dans un gaz rare (Ne, Ar, Kr et Xe). Dans le cas de l'argon on observe la formation de l'excimère ArOD. On met en évidence une prédissociation dans le premier état excité du chlorure de magnésium lors de sa photodissociation.
Small molecules photodynamics : photodissociation of water, observation of arod exciplexe, reactivity of magnesium
This work is concerned with several aspects of reaction dynamics : photodissociation of H₂O and D₂O, observation of the ArOD van der Waals molecule and reactivity of Magnesium atoms. The photodissociation of H₂O and D₂O near the threshold for production of excited OH/OD (A²Σ⁺) fragments has been studied by two-photon excitation of the B ̃ ¹A₁ state at 266nm. The distribution of rotationnal population obtained seems to confirm the existence of long-lived trajectories. When the dissociation process is initiated with a small energy excess, as suggested by quantum mechanical calculations on realistic potential surfaces. When D₂O was dissociated in presence of Argon, an excimer emission from the van der Waals ArOD molecule has been observed. This band was attributed to the transition from the first excited (linear) state to the ground L-shaped state. The emission profile was succesfully simulated using a recently published potential for the excited state and modeling the ground state potent by the X²Σ⁺ground state of ArF. The reactions of Mg (¹S, ³P) with Cl₂and various chlorinated compounds have been studied by LIF and spectral dispersion of the MgCl chemiluminescence reaction product. Rovibronic population distributions were extracted from the experimental spectra, using simulation and inversion procedures. The dynamics of the Mg(¹S)+Cl₂reaction was reinvestigated and compared with the dynamics of the Mg(³P)+ Cl₂chemiluminescence channel. The derived population distributions are consistent with the short distance harpooning mechanism suggested in a previous work of B. Bourguignon, M-A. Gargoura, J. Rostas and G. Taieb.