Scanned energy mode photoelectron diffraction spectra, collected at normal emission over an energy range typically in excess of 300 eV, are presented for 1s photoemission from O on Cu(100) and from O, N, and C in ordered structures on Ni(100). Double-scattering curved wave cluster calculations are used to analyze these data. In all cases adsorption in a hollow site is favored, but the only simple case of chemisorption appears to be Ni(100)c(2×2)O. All the other structures appear to involve adsorbate-induced substrate reconstruction, in which important ingredients appear to be expansion of the top metal layer, and lateral movements within this layer.