Shock wave and modelling study of the unimolecular dissociation of Si(CH3)2F2: an access to spectroscopic and kinetic properties of SiF2. Issue 39 (29th September 2021)

• Record Type: Journal Article
• Authors: Cobos, C. J.; Sölter, L.; Tellbach, E.; Troe, J.
• Is Part Of: Physical chemistry chemical physics. Volume 23:Issue 39(2021)
• Page Start: 22437
• Page End: 22442
• Publication Date: 2021-09-29
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp03298d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Falloff curves of the unimolecular dissociation of Si(CH3 )2 F2 are determined in shock waves and compared to modelling results. High-temperature UV absorption cross sections of SiF2 are also derived. Abstract : The thermal dissociation of Si(CH3 )2 F2 was studied in shock waves between 1400 and 1900 K. UV absorption-time profiles of its dissociation products SiF2 and CH3 were monitored. The reaction proceeds as a unimolecular process not far from the high-pressure limit. Comparing modelled and experimental results, an asymmetric representation of the falloff curves was shown to be most realistic. Modelled limiting high-pressure rate constants agreed well with the experimental data. The UV absorption spectrum of SiF2 was shown to be quasi-continuous, with a maximum near 222 nm and a wavelength-integrated absorption cross section of 4.3 (±1) × 10 −23 cm 3 (between 195 and 255 nm, base e), the latter being consistent with radiative lifetimes from the literature. Experiments over the range 1900–3200 K showed that SiF2 was not consumed by a simple bond fission SiF2 →SiF + F, but by a bimolecular reaction SiF2 + SiF2 → SiF + SiF3 (rate constant in the range 10 11 –10 12 cm 3 mol −1 s −1 ), followed by the unimolecular dissociation SiF3 → SiF2 + F such that the reaction becomes catalyzed by the reactant SiF2 . The analogy to a pathway CF2 + CF2 → CF + CF3, followed by CF3 → CF2 + F, in high-temperature fluorocarbon chemistry is stressed. Besides the high-temperature absorption cross sections of SiF2, analogous data for SiF are also reported.