Dynamics of the reaction CH2I + O(2)probedviainfrared emission of CO, CO2, OH and H2CO

Abstract

The reaction CH2I + O(2)has been widely employed recently for the production of the simplest Criegee intermediate CH2OO in laboratories, but the detailed dynamics of this reaction have been little explored. Infrared emission of several products of this reaction, initiated on irradiation of CH(2)I(2)and O-2(similar to 8 Torr) in a flowing mixture at 308 or 248 nm, was recorded with a step-scan Fourier-transform spectrometer; possible routes of formation were identified according to the observed vibrational distribution of products and published theoretical potential-energy schemes. Upon irradiation at 308 nm, Boltzmann distributions of CO (v <= 5,J <= 19) with an average vibrational energy of 32 +/- 3 kJ mol(-1)and OH (v <= 3,J <= 5.5) with an average vibrational energy of 29 +/- 4 kJ mol(-1)were observed and assigned to the decomposition of HCOOH* to form CO + H2O and OH + HCO, respectively. The broadband emission of CO(2)was simulated with two vibrational distributions of average energies (91 +/- 4) and (147 +/- 8) kJ mol(-1)and assigned to be produced from the decomposition of HCOOH* and methylene bis(oxy), respectively. Upon irradiation of samples at 248 nm, the emission of OH and CO(2)showed similar distributions with slightly greater energies, but the distribution of CO (v <= 11,J <= 19) became bimodal with average vibrational energies of (23 +/- 4) and (107 +/- 29) kJ mol(-1), and branching (56 +/- 5) : (44 +/- 5). The additional large-vcomponent is assigned to be produced from a secondary reaction HCO + O(2)to form CO + HO2; HCO is a coproduct of OH. The branching between CO and OH is (50 +/- 5) : (50 +/- 5) at 308 nm and (64 +/- 5) : (36 +/- 4) at 248 nm, consistent with the mechanism according to which an additional channel to produce CO opens at 248 nm. Highly internally excited H2CO was also observed. With O(2)at 16 Torr, the extrapolated nascent internal distributions are similar to those with O(2)at 8 Torr except for a slight quenching effect.