AbstractAngle-resolved photoemission extended fine structure (ARPEFS) was used to determine the structure of c(2×2)P/Fe(100) for the first time. P 1s core-level photoemission data were collected normal to the (100) surface and 45° off-normal along the [011] direction at room temperature. A close analysis of the auto-regressive linear prediction based Fourier transform and multiple-scattering spherical-wave calculations indicate that the P atoms adsorb in the high-coordination four-fold hollow sites. The P atoms bond 1.02 Å above the first layer of Fe atoms and the Fe-P-Fe bond angle is 140.6°. Additionally, it was determined that there is no expansion of the Fe surface. Self-consistent-field Xα scattered wave calculations were performed for the c(2×2)P/Fe(100) and the c(2×2)S/Fe(100) systems. These independent results are in excellent agreement with this P/Fe structure and the S/Fe structure previously published, confirming the ARPEFS determination that the Fe1-Fe2 interlayer spacing is contracted from the bulk value for S/Fe but not for P/Fe.