Dynamic multiscaling of the reaction-diffusion front for mA+nB-->0.

We consider the reaction zone that grows between separated regions of diffusing species A and B that react according to mA + nB → 0, within the framework of the mean-fieldlike reaction-diffusion equations. For distances from the centre of the reaction zone much smaller than the diffusion length XD ≡ √ Dt, the particle density profiles are described by the scaling forms predicted by a quasistatic approximation, whereas they have a diffusive cutoff at a distance of order XD. This cutoff, and the power-law decay of the quasistatic profiles, give rise to multiscaling behaviour, with anomalous values for the exponents describing the moments of the density and reaction profiles. Numerical solutions of the reaction-diffusion equations are in good quantitative agreement with the predictions of this theory. PACS numbers: 82.40.-g, 82.30.-b, 02.30.Jr, 02.70.Bf Typeset using REVTEX 1