Atmospheric Chemistry of Dimethyl Carbonate:  Reaction with OH Radicals, UV Spectra of CH 3 OC(O)OCH 2 and CH 3 OC(O)OCH 2 O 2 Radicals, Reactions of CH 3 OC(O)OCH 2 O 2 with NO and NO 2 , and Fate of CH 3 OC(O)OCH 2 O Radicals (original) (raw)

1997, The Journal of Physical Chemistry A

A flash photolysis-resonance fluorescence technique was used to study the rate constant for the reaction of OH radicals with dimethyl carbonate over the temperature range 252-370 K. The rate constant exhibited a weak temperature dependence, increasing at both low and high temperature from a minimum value of approximately 3.1 × 10 -13 cm 3 molecule -1 s -1 near room temperature. Pulse radiolysis/transient UV absorption techniques were used to study the ultraviolet absorption spectra and kinetics of CH 3 OC(O)OCH 2 and CH 3 OC(O)CH 2 O 2 radicals at 296 K. Absorption cross sections of CH 3 OC(O)OCH 2 and CH 3 OC(O)OCH 2 O 2 at 250 nm were (3.16 ( 0.34) × 10 -18 and (3.04 ( 0.43) × 10 -18 cm 2 molecule -1 , respectively. Rate constants measured for the self-reactions of CH 3 OC(O)OCH 2 and CH 3 OC(O)OCH 2 O 2 radicals and reactions of CH 3 OC(O)OCH 2 O 2 radicals with NO and NO 2 were (5.6 ( 1.1) × 10 -11 , (1.27 ( 0.21) × 10 -11 , (1.2 ( 0.2) × 10 -11 , and (1.2 ( 0.2) × 10 -11 cm 3 molecule -1 s -1 , respectively. The rate constant for reaction of F atoms with dimethyl carbonate was determined by a pulse radiolysis absolute rate technique to be (6.1 ( 0.9) × 10 -11 cm 3 molecule -1 s -1 . A FTIR smog chamber system was used to show that, in 760 Torr of air at 296 K, CH 3 OC(O)OCH 2 O radicals are lost via three competing processes: 42 ( 15% via reaction with O 2 , 14 ( 2% via H atom elimination, and 44 ( 10% via decomposition and/or isomerization. Relative rate techniques were used to measure rate constants for the reactions of F atoms with CH 3 OC(O)OCH 3 , (6.4 ( 1.4) × 10 -11 cm 3 molecule -1 s -1 , and Cl atoms with CH 3 OC O)OCH 3 , CH 3 OC(O)OCH 2 Cl, CH 3 OC(O)-OCHO, and HC(O)OC(O)OCHO, (2.3 ( 0.8) × 10 -12 , (4.6 ( 2.8) × 10 -13 , (1.7 ( 0.1) × 10 -13 , and (1.7 ( 0.1) × 10 -14 cm 3 molecule -1 s -1 , respectively. Results are discussed in the context of the atmospheric chemistry of CH 3 OC(O)OCH 3 . X Abstract published in AdVance ACS Abstracts, April 15, 1997. CH 3 OC(O)OCH 3 + OH f CH 3 OC(O)OCH 2 + H 2 O (1) 3514