Observation of Adducts in the Reaction of Cl Atoms with XCH₂I (X = H, CH₃, Cl, Br, I) Using Cavity Ring-Down Spectroscopy

Abstract

The reactions of Cl atoms with XCH2I (X = H, CH3, Cl, Br, I) have been studied using cavity ring-down spectroscopy in 25-125 Torr total pressure of N2 diluent at 250 K. Formation of the XCH2I-Cl adduct is the dominant channel in all reactions. The visible absorption spectrum of the XCH2I-Cl adduct was recorded at 405-632 nm. Absorption cross-sections at 435 nm are as follows (in units of 10(-18) cm2 molecule(-1)): 12 for CH3I, 21 for CH3CH2I, 3.7 for CH2ICl, 7.1 for CH2IBr, and 3.7 for CH2I2. Rate constants for the reaction of Cl with CH3I were determined from rise profiles of the CH3I-Cl adduct. k(Cl + CH3I) increases from (0.4 +/- 0.1) x 10(-11) at 25 Torr to (2.0 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1) at 125 Torr of N2 diluent. There is no discernible reaction of the CH3I-Cl adduct with 5-10 Torr of O2. Evidence for the formation of an adduct following the reaction of Cl atoms with CF3I and CH3Br was sought but not found. Absorption attributable to the formation of the XCH2I-Cl adduct following the reaction of Cl atoms with XCH2I (X = H, CH3, Br, I) was measured as a function of temperature over the range 250-320 K.

UV photodissociation dynamics of CHI2Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate

“…The lifetime of CH2I2 due to reaction with either Cl and OH radicals is estimated to be 46 and 62 hours, respectively. 90,91 If the reactivity for CHI2Cl is similar to that of CH2I2, photolysis is likely to be the major gas-phase sink for CHI2Cl produced in surface seawater.…”

Absolute Rate Coefficient Determination and Reaction Mechanism Investigation for the Reaction of Cl Atoms with CH2I2 and the Oxidation Mechanism of CH2I Radicals

“…21,55 Structural and spectroscopic data of XCH 2 I-Cl adducts (X ) H, Cl, Br, I, CH 3 , CH 3 CH 2 , n-C 3 H 7 , i-C 3 H 7 , n-C 4 H 9 , C 6 H 5 , CH 3 O) have been reported in several experimental and theoretical studies. 16,17,[20][21][22]24 In particular, the formation of the ICH 2 I-Cl adduct has been recently observed at 25 -125 Torr of N 2 over the temperature range 250-320 K by cavity ring-down spectroscopy. 16 The fluorescence spectrum of the ICH 2 I-Cl adduct has been also reported, and its fluorescence lifetime at zero pressure was found to be ∼30 ns.…”

“…16,17,[20][21][22]24 In particular, the formation of the ICH 2 I-Cl adduct has been recently observed at 25 -125 Torr of N 2 over the temperature range 250-320 K by cavity ring-down spectroscopy. 16 The fluorescence spectrum of the ICH 2 I-Cl adduct has been also reported, and its fluorescence lifetime at zero pressure was found to be ∼30 ns. 15 The calculated geometry of the ICH 2 I-Cl adduct in the present study shows a slight perturbation of the parent CH 2 I 2 structural parameters with an I-Cl bond length of 2.812 Å, a C-I-Cl bond angle of 79.89 degrees and an I-C-I-Cl dihedral angle of 180 degrees (Cl atom directed away from the other I atom).…”

“…15 In general, experimental and theoretical studies have suggested the presence of attractive forces between Cl atoms with iodinated molecules, which may lead to adducts possessing weak I-Cl bonds. [16][17][18][19][20][21][22][23][24] For Cl atom reactions, pathways proceeding via adduct formation (besides direct abstraction pathways) may enhance the overall rate coefficient and affect the reaction mechanism as well as the branching ratios.…”

A Theoretical Study of the X-Abstraction Reactions (X = H, Br, or I) from CH2IBr by OH Radicals: Implications for Atmospheric Chemistry

“…To assess the role played by CH 2 IBr in atmospheric chemistry, kinetic and mechanistic information concerning their reactions with atmospherically relevant species such as OH radicals and Cl atoms is needed. Only the formation of the adduct in the reaction of Cl atoms with CH 2 IBr was measured as a function of temperature over the range 250-320 K using cavity ringdown spectroscopy [39]. No kinetic data are available in the literature.…”