Shock wave and modelling study of the unimolecular dissociation of Si(CH₃)₂F₂: an access to spectroscopic and kinetic properties of SiF₂

The thermal dissociation of Si(CH₃)₂F₂ 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 cm³ (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 10¹¹-10¹² cm³ 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.Facultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The Thermal Dissociation-Recombination Reactions of SiF4, SiF3, and SiF2: A Shock Wave and Theoretical Modeling Study

Monitoring UV absorption signals of SiF2and SiF, the thermal dissociation reactions of SiF4and SiF2were studied in shock waves. Rationalizing the experimental observations by standard unimolecular rate theory in combination with quantum-chemical calculations of the reaction potentials, rate constants for the thermal dissociation reactions of SiF4, SiF3, and SiF2and their reverse recombination reactions were determined over broad temperature and pressure ranges. A comparison of fluorosilicon and fluorocarbon chemistry was finally made.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Sölter, Lars. Universität Göttingen; Alemania. Max-Planck-Institut für Multidisziplinäre Naturwissenschaften; AlemaniaFil: Tellbach, Elsa. Universität Göttingen; Alemania. Max-Planck-Institut für Multidisziplinäre Naturwissenschaften; AlemaniaFil: Troe, Jürgen. Universität Göttingen; Alemania. Max-Planck-Institut für Multidisziplinäre Naturwissenschaften; Alemani

Shock wave and modelling study of the UV spectra of perfluorocarbon iodides and perfluorocarbon radicals

The UV absorption spectrum of C2F5I was studied in shock waves over the temperature range 580–1200 K and, together with room temperature data, was represented in extended Sulzer–Wieland form. As a case study, the work illustrates the properties of high-temperature UV absorption continua for use in kinetics experiments in shock waves. A comparison with experimental data for CF3I and their representation is made. Quantum-chemical model calculations of positions and oscillator strengths are tested and, besides CF3I and C2F5I, applied also to spectra of C2F4I, C2F4, CF2I, C2F2, C2F, CF2, CFI, CF, and IF. Likewise, modelling and experimental results for the high-temperature UV absorption spectra of CF3 and C2F5 radicals are considered.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hintzer, Klaus. Dyneon GmbH; AlemaniaFil: Sölter, Lars. Universität Göttingen; AlemaniaFil: Tellbach, Elsa. Universität Göttingen; AlemaniaFil: Thaler, Arne. Dyneon GmbH; AlemaniaFil: Troe, Jürgen. Universität Göttingen; Alemania. Max-Planck-Institut für biophysikalische Chemie; Alemani