No abstract

La réaction de Belousov-Zhabotinsky donne spontanément naissance en couche mince à des structures ayant la forme de cibles. On présente les résultats d'une étude expérimentale statistique de ce type de structure conduite en milieu oscillant. Aucune des approches théoriques existantes ne rend convenablement compte des observations réalisées, même du seul point de vue qualitatif. L'origine de la rupture de symétrie du milieu ne peut donc pas encore être élucidée. Un approfondissement de la théorie et un renouvellement des voies de l'expérience demeurent nécessaires

We report measurements on the dispersion relation for chemical trigger waves propagating in an oscillatory Belousov-Zhabotinsky reacting medium. The waves are induced by a temperature perturbation (laser heating). The results are in qualitative agreement with a theory of such waves in an excitable medium.of the absorption from the ground state to the second excited '( , *) (S)*1) state in the vapor phase at room temperature.The decay rates at several vibronic levels of were evaluated from the analysis of line width of the individual vibronic bands in the fluorescence-excitation spectrum in a supersonic free jet. It is considered that the intramolecular proton transfer does not play an important role in the decay process from the state contrary to the case of the first excited '( , *) (Sj*1) state. The observed electronic-state dependence of the intramolecular proton transfer of o-hydroxybenzaldehyde is consistent with the explanation that in contrast to the case of the S0 and S2T' states the enol tautomer is stabilized in the S1*1 state owing to the character of the wave function.

The profile of the waves of chemical activity appearing spontaneously in an oscillating Belousov-Zhabotinsky medium is studied photographically near the core of a target pattern. Digital-image processing allows us to determine for the first time (1) a fairly constant width, equal to 88 ± 16 µ , (2) a monotonously growing amplitude, prior to saturation, at about 1.8 mm from the center, and (3) a slight, but significant increase in the velocity as the wave spreads.

No abstract