Direct rate-constant measurements and theoretical insight into the mechanism of the reactions H + hexamethyldisiloxane and H + tetramethyldisiloxane*

ABSTRACT

Shock-tube experiments were conducted to determine rate-coefficient data of the H-atom abstraction reactions H + HMDSO (hexamethyldisiloxane) → H₂ + HMDSO_−H and H + TMDSO (tetramethyldisiloxane) → H₂ + TMDSO_−H. The experiments comprised a temperature range of 1109–1240 K and pressures between 1.2 and 1.5 bar. In all experiments, C₂H₅I was used as a precursor for H atoms. H-atom concentrations were measured with atomic resonance absorption spectrometry (ARAS) and rate-coefficient data were obtained from pseudo-first-order analysis of temporal H-atom concentration profiles. Experimental total rate-coefficients were well represented by the following Arrhenius equations: k_total,HMDSO(T) = 10^{−9.49±0.36} exp(−32.4 ± 8.1 kJmol⁻¹/RT) cm³molecule⁻¹s⁻¹ for H + HMDSO and k_total,TMDSO(T) = 10^{−8.00±0.36} exp(−53.3 ± 7.9 kJ mol⁻¹/RT) cm³molecule⁻¹s⁻¹ for H + TMDSO. Multiple reaction channels were explored by computations at G4//B3lyp-D3BJ level of theory.

GRAPHICAL ABSTRACT

KEYWORDS:

• Shock tube
• chemical kinetics
• siloxanes
• transition state theory
• RRKM/ME modelling

Acknowledgements

The authors thank Prof. Jürgen Wolfrum (PCI, University of Heidelberg) for stimulating discussions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We gratefully acknowledge financial support by the German Research Foundation (DFG) within the Research unit FOR 2284 ‘Model-based scalable gas-phase synthesis of complex nanoparticles’ [project No. 262219004].