CH2OO Criegee intermediate UV absorption cross-sections and kinetics of CH2OO + CH2OO and CH2OO + I as a function of pressure

The UV absorption cross-sections of the Criegee intermediate CH2OO, and kinetics of the CH2OO self-reaction and the reaction of CH2OO with I are reported as a function of pressure at 298 K. Measurements were made using pulsed laser flash photolysis of CH2I2/O-2/N-2 gas mixtures coupled with time-resolved broadband UV absorption spectroscopy at pressures between 6 and 300 Torr. Results give a peak absorption cross-section of (1.37 +/- 0.29) x 10(-17) cm(2) at similar to 340 nm and a rate coefficient for the CH2OO self-reaction of (8.0 +/- 1.1) x 10(-11) cm(3) s(-1), with no significant pressure dependence of the absorption cross-sections or the self-reaction kinetics over the range investigated. The rate coefficient for the reaction between CH2OO and I demonstrates pressure dependence over the range investigated, with a Lindemann fit giving k(0) = (4.4 +/- 1.0) x 10(-29) cm(6) s(-1) and k(infinity) = (6.7 +/- 0.6) x 10(-11) cm(3) s(-1). The origins of IO in the system have been investigated, the implications of which are discussed.