The threshold cross-link density model describes the effect of cross-link density (THETA) on image formation and the relationship of the cross-link density to acid concentration in the resist. This method was used to determine experimentally the reaction order of acid in the cross-linking reaction of negative acid catalyzed resists. The order of the cross-linking reaction in acid effectively modulates the aerial image of the resist by transforming the initial acid concentration defined by the aerial image by a power equal to the reaction order of the acid. The reaction order of the acid catalyzed cross-linking reaction is also determined via the measurement of bulk resist properties. Determining the reaction order by bulk methods generates a quantity that is independent of the effects of acid diffusion in the resist and is similar to that obtained by the threshold cross-link density model. Also described is the effect acid diffusion will have on mitigating the enhancement of the image obtained with large reaction orders. Finally, the effect of developer selectivity is addressed and a method to determine developer selectivity is presented. The effect on the modulation of the initial energy distribution which is defined by the aerial image from diffusion, reaction order, and developer selectivity is described.