Laser induced fluorescence studies of iodine oxide chemistry : Part II. The reactions of IO with CH3O2, CF3O2 and O3

Abstract

The technique of pulsed laser photolysis was coupled to laser induced fluorescence detection of iodine oxide (IO) to measure rate coefficients, k for the reactions IO + CH(3)O(2)--> products (R1, 30-318 Torr N(2)), IO + CF(3)O(2)--> products (R2, 70-80 Torr N(2)), and IO + O(3)--> OIO + O(2) (R3a). Values of k(1) = (2 +/- 1) x 10(-12) cm(3) molecule(-1) s(-1), k(2) = (3.6 +/- 0.8) x 10(-11) cm(3) molecule(-1) s(-1), and k(3a) <5 x 10(-16) cm(3) molecule(-1) s(-1) were obtained at T = 298 K. In the course of this work, the product yield of IO from the reaction of CH(3)O(2) with I was determined to be close to zero, whereas CH(3)OOI was formed efficiently at 70 Torr N(2). Similarly, no evidence was found for IO formation in the CF(3)O(2) + I reaction. An estimate of the rate coefficients k(CH(3)O(2) + I) = 2 x 10(-11) cm(3) molecule(-1) s(-1) and k(CH(3)OOI + I) = 1.5 x 10(-10) cm(3) molecule(-1) s(-1) was also obtained. The results on k(1)-k(3) are compared to the limited number of previous investigations and the implications for the chemistry of the marine boundary layer are briefly discussed.

Iodine chemistry in the troposphere and its effect on ozone

“…h Updated heats of formation for IO, OIO, and CH 3 O 2 (Dooley et al, 2008;Gómez Martín and Plane, 2009;Knyazev and Slagle, 1998) show that the only accessible exothermic product channel of CH 3 O 2 + IO (Drougas and Kosmas, 2007) is CH 3 O + I + O 2 ( H r = −5 ± 6 kJ mol −1 ), consistent with the high yield of I and low yield of OIO found experimentally (Bale et al, 2005;Enami et al, 2006). Sensitivity studies have been carried out using the preferred rate constant for this reaction of 2 × 10 −12 cm 3 molecule −1 s −1 (Dillon et al, 2006b), resulting in an enhancement of the ozone loss of 0.5% in the MBL and of less than 0.1% integrated throughout the troposphere in the J IxOy scenario, and similarly negligible enhancements in the Base scenario. Impacts in the I y partitioning are also very minor.…”

“…[ . It also makes a negative contribution to the radiative flux in the tropical troposphere (Saiz-Lopez et al, 2012b), and produces higher-order iodine oxides (I x O y ) which have been proposed to participate in the formation of ultrafine aerosol particles in coastal environments (Hoffmann et al, 2001;O'Dowd et al, 2002;Jimenez et al, 2003;McFiggans et al, 2004Pechtl et (Atkinson et al, 2007); 2 Dillon et al, 2006b;3 JPL-2010(Sander et al, 20114 Gómez Martín et al, 2007;5 Kaltsoyannis 6 Gálvez et al, 2013;7 Bösch et al, 2003;8 Gómez Martín and Plane, 2009;9 Chambers et al, 1992;10 Chameides and Davis, 1980;11 Dillon et al, 2006a;12 McFiggans et al, 2000;13 Jenkin et al, 1985;14 Plane et al, 2006;15 Allan and Plane, 2002;16 Lancar et al, 1991;17 Laszlo et al, 1997;18 Bedjanian et al, 1997;19 Gilles et al, 1997;20 Dillon et al, 2008. a The empirical expressions of the form w 1 · exp (w 2 · T ) were obtained by non-linear least squares fitting of Rice-Ramsperger-Kassel-Marcus (RRKM) theoretical results for the indicated reaction rate constants and thermal dissociation rates in the (27-1013) hPa pressure range. RRKM calculations were carried out using the MESMER algorithm (Glowacki et al, 2012) as indicated in the corresponding references (e.g.…”

A Multidimensional Study of the Reaction CH2I+O2: Products and Atmospheric Implications

“…Figure 12, where it is noted that CH 2 O is a major product of reaction (R4a),~70 %. It is interesting to compare reaction (R8) with that of CH 3 O 2 + I, which was studied by Dillon et al [40] who reported efficient formation of CH 3 O 2 I. We speculate that the weak I bond in CH 2 IO 2 allows the bimolecular channel to operate (R4a) which is not the case for CH 3 O 2 , where the association channel CH 3 OOI is found to be dominant.…”

Combined experimental and theoretical investisgation of the reactivity of CH3O2 and C2H5O2 radicals

“…(c) The reaction of CH3O2 radicals with I-atoms has first been mentioned by Jenkin and Cox 108 and has more recently been studied in detail by Dillon et al 109 . It was found that CH3O2 radicals catalyze the recombination of I-atoms in a Chaperon-like mechanism.…”

“…It is known that I-atoms recombine rapidly with CH3O2 radicals to form CH3O2I 108 . In a recent work, Dillon et al 109 have shown that in a subsequent reaction CH3O2I molecules react very rapidly (1.5 × 10 −10 cm 3 s −1 ) with I-atoms, leading back to CH3O2 radicals and I2. A model shows that under our conditions this reaction sequence leads to a small decrease in CH3O2 concentration: a steady state concentration of CH3O2I…”