Rate Constants for the Gas-Phase Reactions of OH Radicals with Dimethyl Phosphonate over the Temperature Range of 278−351 K and for a Series of Other Organophosphorus Compounds at ∼280 K

Abstract

Rate constants for the gas-phase reactions of OH radicals with dimethyl phosphonate [DMHP; (CH3O)2P(O)H] were measured over the temperature range of 278-351 K at atmospheric pressure of air using a relative rate method with 4-methyl-2-pentanone as the reference compound. The Arrhenius expression obtained was 1.01 x 10(-12) e((474 +/- 159)/T) cm(3) molecule(-1) s(-1), where the indicated error is two least-squares standard deviations and does not include uncertainties in the rate constants for the reference compound. Rate constants for the gas-phase reactions of OH radicals with dimethyl methylphosphonate [DMMP, (CH3O)2P(O)CH3], dimethyl ethylphosphonate [DMEP, (CH3O)2P(O)C2H5], diethyl methylphosphonate [DEMP, (C2H5O)2P(O)CH3], diethyl ethylphosphonate [DEEP, (C2H5O)2P(O)C2H5], and triethyl phosphate [TEP, (C2H5O)3PO] were also measured at 278 and/or 283 K for comparison with a previous study (Aschmann, S. M.; Long, W. D.; Atkinson, R. J. Phys. Chem. A, 2006, 110, 7393). With the experimental procedures employed, experiments conducted at temperatures below the dew point where a water film was present on the outside of the Teflon reaction chamber resulted in measured rate constants which were significantly higher than those expected from the extrapolation of rate data obtained at temperatures (283-348 K) above the dew point. Using rate constants measured at > or = 283 K, the resulting Arrhenius expressions (in cm(3) molecule(-1) s(-1) units) are 6.25 x 10(-14) e((1538 +/- 112)/T) for DMMP (283-348 K), 9.03 x 10(-14) e((1539 +/- 27)/T) for DMEP (283-348 K), 4.35 x 10(-13) e((1444 +/- 148)/T) for DEMP (283-348 K), 4.08 x 10(-13) e((1485 +/- 328)/T) for DEEP (283-348 K), and 4.07 x 10(-13) e((1448 +/- 145)/T) for TEP (283-347 K), where the indicated errors are as above. Aerosol formation at 296 +/- 2 K from the reactions of OH radicals with these organophosphorus compounds was relatively minor, with aerosol yields of < or = 8% in all cases.