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T. Beiderhase, Walter Hack, Karlheinz Hoyermann, Matthias Olzmann

Gas-Phase Kinetics of the Self Reactions of the Radicals CH₂F and CHF₂

Fluorinated hydrocarbon radical-radical reactions in the gas phase have been studied at low pressure (0.5 ≤ p/mbar ≤ 2) and low temperature (253 ≤ T/K ≤ 333) using the discharge flow reactor molecular beam sampling mass spectrometry (MS) technique. Stable and labile species have been detected by MS applying low energy electron impact as well as multiphoton ionisation.
For the combination reaction
CH₂F + CH₂F → products (1)
the rate coefficient k₁ = (7.0±0.8) × 10¹² (T/298)^(-3.9±1.0) cm³/mol × s was determined. At low pressure the HF elimination pathway (1b)
CH₂F + CH₂F → C₂H₃F + HF (1b)
is the main channel (k(1b)/k₁ = (0.82±0.015)).
For the CHF₂ radical self reaction
CHF₂ + CHF₂ → products (2)
the rate coefficient was measured as k₂ = (1.7±0.5) × 10¹³ exp((-555±89)/T) cm³/mol × s. The stabilisation of C₂H₂F₄* is the main reaction pathway (2a) (k_2a/k₂ ≥ 0.5), the HF elimination is of minor importance (k_2b/k₂ = 0.2).
No pressure dependence of k₁ and k₂ was observed in the limited pressure range.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 214, 05/2000
Pages: 625

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