Kinetic and mechanistic study of the reaction of atomic chlorine with dimethyl sulfide

Abstract

4) Orban, M.; Kijrb, E. K b b , E.; Noyes, R. M. J. Am. Chem. Soc. 1972, 94, Trans. 1992,88, 917. S = 2 k~l / k~6 / &~3 &~ = 9.52 x 10" b = 2kB6kB9[R]/k~lkW[BrOS-] = 0.545 K 3 k~z / k~l = 1.6 6 = k~l / 2 k~6 = 3.33 x r = k~i k~a / k~k~s = 0.101 Q = 2 k~s k~/ k~, ' = 0.0101 0 = kB,/kB6 = 1.667 x lo3 B = k~3 / 2 k~6 = 500 T,,, = kW[Br03-]trea = 3.91t,/s Repistry No. BrO,-, 15541-45-4; gallic acid, 149-91-7; ferroin, 14708-99-7.Timaresolved fluorescmCe detection Of Cl(9j) following 266-nm laser flash photd~is Of Cl~cO/CH$CH~(DMS)/N~ mixtures has been employed to study the kinetics of the title reaction over the temperature and pressure ranges 240-421 K and 3-700 Torr. The reaction is found to be very fast, occumng on essentially every C1(2PJ) + DMS encounter. The reaction rate increases with decreasing temperature and shows a significant pressure dependence. At 297 K, for example, the rate coefficient increases from a low-pressure limit value of approximately 1.8 X cm3 molecule-' s-' to a value of (3.3 f 0.5) X cm3 molecule-' s-l at P = 700 Torr. A few experiments were carried out with CD3SCD3 or C2H5SC2Hs replacing DMS as the sulfide reactant; within experimental uncertainty, no dependence of the rate coefficient on the identity of the sulfide reactant was observed. In a separate study, time-resolved tunable diode laser spectroscopic detection of HCl has been coupled with 248-nm laser flash photolysis of Cl&O/DMS/COz/Nz mixtures to measure the HCl product yield from the title reaction as a function of pressure at T = 297 K. The HCl yield approaches unity as P -0 but decreases with increasing pressure to a value of -0.5 at P = 203 Torr. The yield experiments demonstrate that hydrogen abstraction is the dominant reaction mechanism in the low-pressure limit. With increasing pressure, stabilization of a (CH3)gCI adduct apparently becomes competitive with the hydrogen abstraction pathway. The fate of the stabilized adduct remains highly uncertain, although it clearly does not dissociate to Cl(9J) or HCl on the time scale of our experiments (several milliseconds). The potential role of the title reaction in marine atmospheric chemistry is discussed.

A kinetics and mechanistic study of the atmospherically relevant reaction between molecular chlorine and dimethyl sulfide (DMS)

“…The minimum detection limits for Ar, DMS and Cl 2 were estimated as 1x10 11 , 3.5x10 11 and 4x10 11 molecules cm -3 respectively. Also for these three gases the pressure range over which the photoelectron signal was linear with pressure in the flow tube was 1x10 11 -1.1x10 14 , 3.5x10 11 -1.6x10 13 and 4x10 11 -1x10 14 molecules cm -3 respectively. (These experiments set the detection limit as a signal : noise ratio of 2 with an integration time of 1 sec.…”

“…Stickel et al (13), in a study of reaction (2) using time-resolved detection of Cl atoms, reported that the branching ratio of reaction (2a) approaches unity with decreasing total pressure and k 2 increases with pressure. Both reactions (2a) and (2b) are expected to have large rate constants, as they proceed without a barrier, whereas reaction 2c, decomposition of (CH 3 ) 2 SCl to CH 3 and CH 3 SCl, is very slow because it has a high activation energy barrier of ≈18 kcal.mol -1 (16).…”

“…A modelling study conducted in this work found that, shortly after sunrise, the oxidation rate of DMS by Cl, produced by photolysis of Cl 2 , could under favourable conditions, be an order of magnitude higher than the rate of oxidation by OH. The rate constant for the reaction between Cl atoms and DMS at 298 K and 1 torr pressure has been measured as (6.9 ± 1.3) x 10 -11 cm 3 molecule -1 s -1 using discharge-flow mass spectrometry (12), and at 3 torr pressure and at 297 K it has been measured as (1.8 ± 0.3) x10 -10 cm 3 molecule -1 s -1 using time-resolved resonance detection of Cl (13). A more recent study using cavity ring-down spectroscopy (14) determined the rate constant at atmospheric pressure as (3.6 ± 0.2) x10 -10 cm 3 molecule -1 s -1 and a low-pressure limit rate constant consistent with that found in references (12) and (13).…”

“…The rate constant for the reaction between Cl atoms and DMS at 298 K and 1 torr pressure has been measured as (6.9 ± 1.3) x 10 -11 cm 3 molecule -1 s -1 using discharge-flow mass spectrometry (12), and at 3 torr pressure and at 297 K it has been measured as (1.8 ± 0.3) x10 -10 cm 3 molecule -1 s -1 using time-resolved resonance detection of Cl (13). A more recent study using cavity ring-down spectroscopy (14) determined the rate constant at atmospheric pressure as (3.6 ± 0.2) x10 -10 cm 3 molecule -1 s -1 and a low-pressure limit rate constant consistent with that found in references (12) and (13). It has been found that the Cl + DMS reaction, reaction (2), proceeds via two routes, a direct stripping channel (2a) that proceeds without a barrier to give CH 3 SCH 2 and HCl and an addition channel (2b) to give (CH 3 ) 2 SCl (13-16).…”

Kinetics and mechanism of the reaction between atomic chlorine and dimethyl selenide; comparison with the reaction between atomic chlorine and dimethyl sulfide

“…The values obtained were used along with the thermal corrections obtained from the frequency calculations, to calculate the value of Δ r H o at 298 K for reactions (8) - (15) and reactions (17) and (18).…”