Before revision:  The RDME has been shown to have the drawback of losing bimolecular reactions in the limit that the lattice spacing approaches zero ( in two or more dimensions ).
After revision:  The RDME is often interpreted as an approximation to spatially-continuous models in which molecules move by Brownian motion and react by one of several mechanisms when sufficiently close. In the limit that the lattice spacing approaches zero ( in two or more dimensions ).