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

The initiation of chemical reaction-diffusion waves by visible light of wavelength λ = 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 resting steady state and in the recovering tail of a wave. With high loading, waves can only be initiated in the 'vulnerable' region behind an existing wavefront. The mechanism of this initiation is discussed in terms of the photoreduction 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.