Silicon was implanted with 2 MeV O+ ions with doses covering the range from 1 x 10(17) to 2 x 10(18) O+ cm(-2), at an implantation temperature of 700 degrees C. Subsequently, samples were capped and annealed at 1300 degrees C. Infrared reflectance spectroscopy has been used in order to characterize the as-implanted and annealed samples. The optical modeling of the multilayer structures and the data reduction procedure are given in detail. The thickness, chemical composition, crystallinity, interface macroscopic roughness, and refractive index profiles are quantified. It is shown that infrared reflectance spectroscopy is a quick, nondestructive, analytical, and precise method for characterizing high energy separation by implantation of oxygen (SIMOX) structures. Cross correlation with H+ beam Rutherford backscattering/channeling, secondary ion mass spectroscopy, and cross-sectional transmission electron microscopy results, gives good agreement. The formation of oxide in the high energy region follows the same basic rules as in the standard SIMOX case. No anomalous oxygen diffusion was observed during annealing and a buried layer formed during annealing even for the lowest dose. It is found that the microstructure of the annealed samples is strongly dependent on the implantation conditions such as beam current density and that even for the highest dose of 2 x 10(18) O+ cm(-2), a continuous stoichiometric silicon dioxide layer has not formed after annealing.