The molecular structures of dehydrated group 5−7 transition metal oxides (V2O5, Nb2O5, CrO3, MoO3, WO3, Re2O7) supported on SiO2 were investigated with time-resolved 18O−16O exchange in situ Raman spectroscopy measurements. The supported group 5−7 dehydrated surface transition metal oxides were exclusively present as isolated species on SiO2 because of the absence of bridging M−O−M vibrations. The SiO2-supported group 5 (VOx and NbOx) surface metal oxides exhibit band splitting into two Raman vibrations (M16O and M18O), which is consistent with monoxo surface OM(−O−Si)3 species. The SiO2-supported group 6 (CrOx, MoOx, and WOx) surface metal oxides consist of both monoxo OM(−O−Si)4 and dioxo (O)2M(−O−Si)2 structures. The dioxo surface species give rise to triplet band splitting corresponding to M(16O)2, M(18O)2, and 18OM16O. Identification of the intermediate surface 18OM16O struc-ture was guided by recent DFT calculations. The SiO2-supported group 7 (ReOx) metal oxide system exclusively contains trioxo su...