Kinetic Study of IO Radical with RO₂ (R = CH₃, C₂H₅, and CF₃) Using Cavity Ring-Down Spectroscopy

Abstract

The reactions of iodine monoxide radical, IO, with alkyl peroxide radicals, RO(2) (R = CH(3), C(2)H(5), and CF(3)), have been studied using cavity ring-down spectroscopy. The rate constant of the reaction of IO with CH(3)O(2) was determined to be (7.0 +/- 3.0) x 10(-11) cm(3) molecule(-1) s(-1) at 298 K and 100 Torr of N(2) diluent. The quoted uncertainty is two standard deviations. No significant pressure dependence of the rate constant was observed at 30-130 Torr total pressure of N(2) diluent. The temperature dependence of the rate constants was also studied at 213-298 K. The upper limit of the branching ratio of OIO radical formation from IO + CH(3)O(2) was estimated to be <0.1. The reaction rate constants of IO + C(2)H(5)O(2) and IO + CF(3)O(2) were determined to be (14 +/- 6) x 10(-11) and (6.3 +/- 2.7) x 10(-11) cm(3) molecule(-1) s(-1) at 298 K, 100 Torr of N(2) diluent, respectively. The upper limit of the reaction rate constant of IO with CH(3)I was <4 x 10(-14) cm(3) molecule(-1) s(-1).

Iodine chemistry in the troposphere and its effect on ozone

“…3 and 4). 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.…”

Measurement and interpretation of gas phase formaldehyde concentrations obtained during the CHABLIS campaign in coastal Antarctica

“…In this paper we assume that the reaction does not produce HCHO. Measured rate constants for the IO+CH 3 O 2 reaction are in disagreement, with values (molec −1 cm 3 s −1 ) of 6×10 −11 (Bale et al, 2005;298 K), 2×10 −12 (Dillon et al, 2006; 298 K) and 6.9×10 −11 (Enami et al, 2006;267 K). Moreover, the products of the reaction are unknown.…”

Structures, Vibrational Spectra, and Relative Energetics of CH3COIO3 Isomers

“…Two of the experimental studies have shown that the reactions RO 2 ＋IO are fast and may indeed have an important impact on ozone chemistry. Enami et al 13 found the value k＝ (7. 2 , i.e., it is smaller than the former measurements by about 30 times. The difference is quite large, indicating that the system is very complex.…”

“…All studies were unable to determine specific reaction pathways and analyze products and branching ratios. 8 The investigation by Enami et al 13 has produced only an upper limit branching ratio, ＜0.1, for the OIO radical formation. The lack of information about the products and the serious discrepancy over the rate constant measurements, which are directly connected to the atmospheric significance of these reactions, make desirable the theoretical study of the RO 2 ＋IO system and the computational investigation of its reaction pathways.…”