Rate Coefficients for the Cl Atom Gas-Phase Reaction With Permethylsiloxanes (PMS): L2, L3, L4, L5, D3, D4, D5, and D6

IF 1.5 4区化学 Q4 CHEMISTRY, PHYSICAL

International Journal of Chemical Kinetics Pub Date : 2024-12-09 DOI:10.1002/kin.21770

Daniel Van Hoomissen, Aparajeo Chattopadhyay, James B. Burkholder

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Abstract

Rate coefficients, k(T), for the gas-phase Cl atom reaction with hexamethyldisiloxane ((CH₃)₃SiOSi(CH₃)₃, L₂), k₁; octamethyltrisiloxane ([(CH₃)₃SiO]₂Si(CH₃)₂, L₃), k₂; decamethyltetrasiloxane ((CH₃)₃SiO[Si(CH₃)₂O]₂Si(CH₃)₃, L₄, k₃; dodecamethylpentasiloxane ((CH₃)₃SiO[Si(CH₃)₂O]₃Si(CH₃)₃, L₅, k₄; hexamethylcyclotrisiloxane ([-Si(CH₃)₂O-]₃, D₃), k₅; octamethylcyclotetrasiloxane ([-Si(CH₃)₂O-]₄, D₄), k₆; decamethylcyclopentasiloxane ([-Si(CH₃)₂O-]₅, D₅, k₇), and dodecamethylcyclohexasiloxane ([-Si(CH₃)₂O-]₆, D₆, k₈) were measured over a range of temperature (273–363 K) using a pulsed laser photolysis (PLP) – resonance fluorescence (RF) technique. The obtained k(296 K) and Arrhenius expressions with 2σ uncertainties including estimated systematic errors are (in units of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹):

The cyclic permethyl siloxanes (cyclic PMS) were found to be less reactive than the analogous linear permethyl siloxane (linear PMS) with an equal number of CH₃- groups. Both linear and cyclic compounds show a linear relationship between the measured rate coefficient and the number of CH₃- groups in the molecule. A structure–activity relationship (SAR) is presented that reproduces the experimental data to within ∼10% at all temperatures. For [Cl] ≈ 10⁴ atom cm⁻³, an approximate free troposphere abundance, the PMS loss due to Cl atom reaction leads to relatively short estimated lifetimes of 7, 6, 5, 4, 20, 10, 7, and 5 days for L₂, L₃, L₄, L₅, D₃, D₄, D₅, and D₆, respectively. Therefore, the PMSs included in this study are classified as atmospherically very short-lived substances and Cl atom reaction represents a significant loss process.

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来源期刊

International Journal of Chemical Kinetics 化学-物理化学

CiteScore

3.30

自引率

6.70%

发文量

审稿时长

3 months

期刊介绍： As the leading archival journal devoted exclusively to chemical kinetics, the International Journal of Chemical Kinetics publishes original research in gas phase, condensed phase, and polymer reaction kinetics, as well as biochemical and surface kinetics. The Journal seeks to be the primary archive for careful experimental measurements of reaction kinetics, in both simple and complex systems. The Journal also presents new developments in applied theoretical kinetics and publishes large kinetic models, and the algorithms and estimates used in these models. These include methods for handling the large reaction networks important in biochemistry, catalysis, and free radical chemistry. In addition, the Journal explores such topics as the quantitative relationships between molecular structure and chemical reactivity, organic/inorganic chemistry and reaction mechanisms, and the reactive chemistry at interfaces.