Typically, the Dill ABC parameters for optical resist are determined by coating a resist on a nonreflecting substrate and then measuring the change in the intensity of transmitted light at the wavelength of interest as a function of incident energy. Resists absorbance may not be selective in isolating and measuring only the photoactive species, and in some cases changes in absorbance can not be directly correlated to changes in the concentration of the photoactive species. FTIR spectroscopy can directly measure changes in the photoactive species by isolating and measuring absorbance peaks unique to the photoactive species by isolating and measuring absorbance peaks unique to the photoactive species. FTIR, employed in reflectance mode, is not constrained to transparent substrates, but can instead be used with silicon wafers or chrome coated quartz plates. The ability to use these substrates, but can instead be used with silicon wafers or chrome coated quartz plates. The ability to use these substrates is important when determining Dill's C parameter under e-beam exposure where the degree of back-scattered electrons is dependent on the underlying substrate, and the use of quartz is prohibited due to charging considerations. Dill's C parameter is determined for a variety of commercial i-line resist under both e-beam and i-line exposure. The ProABC software, a lithography simulator that extracts ABC parameters through a best fit of model to data, is employed to extract Dill's C parameter. This software has been specially modified to allow FTIR absorbance input.