Wave initiation in the ferroin-catalysed Belousov-Zhabotinsky reaction with visible light

The initiation of chemical reaction-diffusion waves by visible light of wav elength lambda = 632.8 nm from a 20 mW He-Ne laser in the ferroin-catalysed BZ reaction on a polysulfone membrane is reported. With low loading of the catalyst on the membrane, oxidation waves can be initiated from the restin g steady state and in the recovering tail of a wave. With high loading, wav es can only be initiated in the 'vulnerable' region behind an existing wave front. The mechanism of this initiation is discussed in terms of the photor eduction of the metal-ligand catalyst and expressed in terms of a modified Oregonator model. These new observations are in contrast to the inhibitory effect of visible light in the light-sensitive Ru-catalysed BZ system.