The structure of a premixed H-2/O-2/Ar (0.2610.1310.61 by volume) flame doped with dimethyl methyl phosphonate (DMMP) stabilized on a flat burner at 47 Torr has been studied by molecular-beam mass spectrometry and modeling. Using previous experimental measurements, the mechanism for the destruction of trimethyl phosphate (TMP) in H-2/O-2/Ar flames was refined. The present experiments with Twarowski＇s reaction mechanism for hydrogen, oxygen, and phosphorus and Warner and Cool＇s mechanism for the destruction of DMMP, enabled updated kinetic mechanisms for the destruction of both DMMP and TMP in a flame to be developed. Based on the available thermochemical data and using the computer codes PREMIX and CHEMKIN-II, the computer modeling of the destruction of DMMP and TMP in a flame was achieved. Matching the experimental and calculated concentration profiles for all the species found in flames allowed the rate constants for the reactions of intermediates to be evaluated and refined. The final result is that the calculated and measured concentration profiles are in satisfactory agreement for DMMP, TMP, H-2 O-2 H2O, OH, O, H, PO, PO2, HOPO, and HOPO2. The results provide an understanding of important regularities of the destruction of organophosphorus compounds, used here as simulants of sarin in flames. (C) 2000 by The Combustion Institute.