Atmospheric chemistry of isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate.

Rate constants for the reactions of OH radicals with isopropyl methyl methylphosphonate I(CH 3 ) 2 CHOP(O)(CH 3 )OCH 3 ; IMMP] and dimethyl N,N-dimethylphosphoroamidate [(CH 3 O) 2 P(O)N(CH 3 ) 2 ; DMDMPA] have been measured over the temperature range 283-350 K and atmospheric pressure of air using a relative rate method. The rate expressions obtained were 2.72 x 10 -13 e (1642±144)/T cm 3 molecule -1 s -1 (6.72 x 10 -11 cm 3 molecule -1 s -1 at 298 K) for OH + IMMP and 6.05 x 10 -13 e (1185±144)/T cm 3 molecule -1 s -1 (3.23 x 10 -11 cm 3 molecule -1 s -1 at 298 K) for OH + DMDMPA. In addition, rate constants for the reactions of NO 3 radicals and O 3 with IMMP were measured at 296 ± 2 K, of (4.8 ± 2.1) x 10 -16 and <7 × 10 -21 cm 3 molecule -1 s -1 , respectively. Products of the OH radical-initiated reactions were investigated using gas chromatography, in situ atmospheric pressure ionization mass spectrometry (API-MS), and in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH + IMMP reaction, the major initial products appear to be CH 3 OP(O)(CH 3 )OC(O)CH 3 + • CH 3 , with subsequent reactions of the methyl radical in the presence of NO x leading to HCHO, CH 3 ONO, and CH 3 ONO 2 . For the OH + DMDMPA reaction, (CH 3 O) 2 P(O)N(CH 3 )CHO was observed as a significant product. Possible reaction mechanisms are discussed.