A normal incidence X-ray standing wavefield study of the structure of molecular SO 2 on Ni(111) has been conducted, using photoabsorption at both the O and S atoms and real-space site triangulation using {111} scatterer planes both parallel to, and at 70° to, the surface plane. Both O and S atoms are found to be in the vicinity of atop sites, although the S atoms are displaced significantly further from these high symmetry sites. S K-edge NEXAFS confirms an earlier finding that the molecule lies with its molecular plane parallel to the surface. The detailed sites can only be reconciled with a model in which the SO 2 molecules are centred close to hollow sites (with equal occupation of both types of hollow) and the internal conformation of the molecule, especially the OSO bond angle, is significantly different from that of the gas-phase molecule. Specifically, the OSO bond angle is estimated to be no more than 100°, while the data indicate an SO bond-length expansion of 5% or more. This change is attributed to the unusual π-bonding (for which there appears to be no analogue in coordination compounds) and thus partial occupation of the 3b 1 π∗ LUMO of the molecule.