The emissivity of a particulate flame which contains interacting soot particles of size parameters larger than Rayleigh limit and up to Penndorf extension is derived. The flame is assumed to be heavily charged with soot particles and radiation from the flame is mainly dominated by that emitted or absorbed by particles. It is found that interaction mechanisms have no significant effects on the emissivity of the flame. However, for flames containing soot particles of large size parameters, the emissivity deviates considerably from that estimated based on the Rayleigh limit assumption. Also, a modified version of the monochromatic Schmidt method is proposed to predict the temperature and soot concentration of flames which contain interacting soot particles having size parameters larger than Rayleigh limit and up to Penndorf extension.