This paper reports fundamental vibration frequencies for molecular OS03Fz and o s o 4 isolated in argon matrices at low temperatures. Os03Fz is shown to have D3h symmetry on the basis of Raman and IR selection rules, and this conclusion is confirmed by the results of ' 8 0 enrichment studies which demonstrate the presence of an oso3 unit containing three equivalent oxygens. The argon matrix frequencies are 946.5 ( A ; ) , 928.5 (E'), 646 (A;), 619 ( A ; ) 348 (E"), 316.5 (E') 258 ( A ; ) and 206 (E') cm-l. High resolution spectra are also reported for matrix isolated oS1604 (~1963, vz 332, v3 956, and v4 327 cm-I) and for ' 8 0 enriched oso4 species.