Complex refractive indices for nopinone have been inverted from the mid-infrared spectra of laboratory generated aerosols. The particles were formed via homogeneous nucleation, injected into a laminar flow cell, and analyzed by Fourier-transform infrared spectroscopy. The inversion was initiated by using a thin-film spectrum of nopinone to obtain an estimate of the imaginary component of the frequency-dependent refractive indices. The corresponding real components were then determined through the Kramers-Kronig transformation. The refractive indices were then used in a weighted Mie scattering calculation to fit nopinone aerosol extinction spectra that showed evidence of scattering. The inversion results were averaged together to produce the data set reported here from 750 to 5000 cm-1. The nopinone refractive indices are also compared to those reported for carvone, a biosynthesized keto-monoterpene.