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

Abstract

A gas-phase kinetics study of the atmospherically important reaction between Cl 2 and dimethyl sulfide (DMS) Cl 2 + CH 3 SCH 3 → products ----- (1) has been made using a flow-tube interfaced to a photoelectron spectrometer. The rate constant for this reaction has been measured at 1.6 and 3.0 torr at T= (294±2) K as (3.4 ± 0.7) x 10 -14 cm 3 molecule -1 s -1 . Reaction (1) has been found to proceed via an intermediate, (CH 3 ) 2 SCl 2 , to give CH 3 SCH 2 Cl and HCl as the products. The mechanism of this reaction and the structure of the intermediate were investigated using electronic structure calculations. A comparison of the mechanisms of the reactions between Cl atoms and DMS, and Cl 2 and DMS has been made and the relevance of the results to atmospheric chemistry is discussed.

Photoionization studies of reactive intermediates using synchrotron radiation

“…(2). Also, the room temperature rate coefficient of the Cl2 + CH3SCH3 reaction has been measured using PES as the detection method (3).…”

“…However, if the parent ion is observed, its intensity can be monitored as a function of photon energy to obtain an ionization efficiency curve. This can then be used to estimate the associated adiabatic ionization energy (AIE, the difference between the lowest vibrational If the AIEs of ABC and AB can be measured for processes (1) and (3), and the appearance energy (AE) of AB + can be measured for step (2), then from the AE of AB + and the AIE of ABC, the dissociation energy of AB + -C, D(AB + -C), can be calculated, using equation 4:-D(AB + -C) = AE(AB + ) -AIE(ABC) ------ (4) Also, from the AE(AB + ) in equation (2) and the AIE of AB in equation 3, the neutral dissociation energy D(AB-C) can be calculated D(AB-C) = AE(AB + ) -AIE(AB) -------- (5) Thermodynamic cycle calculations of this type have been used extensively to determine heats of formation of reactive intermediates and bond strengths in molecules and ions (9)(10)(11). This information is important in modelling the atmosphere and other environments, and in benchmarking theoretical methods used to calculate these quantities.…”

“…When considering equations (1) to (3) it is important to emphasize, however, that obtaining reliable AEs experimentally is more challenging that obtaining reliable AIEs. The determination of the AIE from a vibrationally resolved PE band is usually reasonably straightforward, particularly if the vibrational envelope can be computed, using potential energy surfaces of the molecule and the ion derived from electronic structure calculations, and there is only a small change in equilibrium geometry between the molecule and the ion.…”

A study of the atmospherically important reactions of dimethylsulfide (DMS) with I2 and ICl using infrared matrix isolation spectroscopy and electronic structure calculations

“…These results were interpreted as the bands at 1040 and 1333 cm À1 being associated with the DMS : ICl complex. The bands associated with monochloroDMS and HCl arise from a small amount of dissociation of ICl into I 2 and Cl 2 with the Cl 2 reacting with DMS to give monochloroDMS and HCl, [22][23][24] and I 2 reacting with DMS to give the DMS : I 2 complex which is in much lower concentration than the DMS : ICl complex.…”

“…photoelectron spectroscopy and electronic structure calculations. [22][23][24] In this present work, these studies are extended to the DMS + I 2 and DMS + ICl reactions. The aim is to determine the reaction mechanism and reaction products, and, if possible, identify reaction intermediates.…”