The structure of the Ni{100}-2 x 2)-C surface has been investigated by time-of-light scattering and recoiling spectrometry (TOF-SARS), low-energy electron diffraction (LEED), and classical scattering simulations, The surface was prepared by chemisorption of either carbon monoxide, benzene, or aniline onto a Ni{100} surface at 600 degrees C. The scattering flux from 4 keV of Ne+ and the recoiling flux of carbon from 4 keV of Ar+ were monitored as a function of the crystal azimuthal angle. An efficient simulation method, which is based on the binary collision approximation and shadowing and blocking effects, has been developed and applied to simulation of the TOF-SARS azimuthal scans. Quantitative values for the geometrical parameters were obtained by using a reliability (R) factor to compare the experimental and simulated azimuthal scans. The results are consistent with a surface structure which consists of 80% of a clock reconstructed (2 x 2)p4g phase and 20% of an unreconstructed (2 x 2) phase. For the reconstructed phase, the Ni atoms rotate in alternating clockwise and anticlockwise directions with the Ni atoms displaced laterally from their original positions by 0.6 +/- 0.1 Angstrom and the C atoms in the 4-fold sites at positions 0.1 +/- 0.1 Angstrom above the plane of Ni atoms. The consequences of these results with respect to heterogeneous catalysis are discussed.