The matrix isolation technique has been combined with theoretical calculations to identify and characterize the photoproducts in the reaction of PH3 With OVCl3 and CrCl2O2. In contrast to previous studies, HCl elimination from an initial complex is not observed. Instead, a number of product bands, some quite intense, were observed and have been assigned to phosphine oxide, H3PO, through the direct 0 atom transfer from the transition metal oxo compound. This identification was supported by extensive isotopic labeling, and by comparison to theoretical calculations. H3PO formed in this manner is cage-paired and interacts with the transition metal fragment (VCl3 or Cl2CrO), leading to a 113 cm(-1) red-shift of the P=O stretching mode relative to isolated monomeric H3PO.