Abstract
The reaction of dichlorodifluoromethane (CF2Cl2) with hydrated electrons (H2O)n − (n = 30–86) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The hydrated electron reacts with CF2Cl2, forming (H2O)mCl− with a rate constant of (8.6 ± 2.2) × 10−10 cm3 s−1, corresponding to an efficiency of 57 ± 15%. The reaction enthalpy was determined using nanocalorimetry, revealing a strongly exothermic reaction with ΔHr(CF2Cl2, 298 K) = −208 ± 41 kJ mol−1. The combination of the measured reaction enthalpy with thermochemical data from the condensed phase yields a C–Cl bond dissociation enthalpy (BDE) ΔHC–Cl(CF2Cl2, 298 K) = 355 ± 41 kJ mol−1 that agrees within error limits with the predicted values from quantum chemical calculations and published BDEs.
Highlights
Since the discovery of the atmospheric ozone hole chlorofluorocarbons (CFCs) have been recognized as one of the important players in ozone depletion.[1,2] The most common CFC is dichlorodifluoromethane (CF2Cl2) that was used in refrigerants due to its high latent heat, non-toxicity and inertness
No adiabatic values are available for neat water clusters, but Donald et al studied the hydration of free electrons in La(H2O)n3+, n = 42–160.74 From this study, they extrapolated a bulk hydration enthalpy of À1.3 eV for the electron, identical to the value suggested for the presolvated electron
This implies that dissociative electron transfer to CF2Cl2 in the condensed phase does not require a presolvated state, which is in agreement with the earlier results from pulse radiolysis in bulk aqueous solution.[27]
Summary
Since the discovery of the atmospheric ozone hole chlorofluorocarbons (CFCs) have been recognized as one of the important players in ozone depletion.[1,2] The most common CFC is dichlorodifluoromethane (CF2Cl2) that was used in refrigerants due to its high latent heat, non-toxicity and inertness. Based on the large enhancement of ClÀ generation from the DET to CFCs on ices, Lu and Sanche[8,9] proposed the cosmic-ray-driven electron reaction model for ozone depletion, short CRE mechanism, as an additional potential source of Cl radicals. This mechanism initiated a controversial debate.[8,10,11,12,13,14,15]. G4 level calculations exhibit an average absolute deviation from experiment of 3.5 kJ molÀ1
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