Atmospheric Reactions of (H)‐ and (D)‐Fluoroalcohols with Chlorine Atoms

Abstract

The reactions of Cl with a series of fluoroalcohols and deuterated fluoroalcohols, CF(3)CH(2)OH (k(4)), CF(3)CH(OH)CH(3) (k(5)), CF(3)CH(OH)CF(3) (k(6)), CF(3)CH(OD)CF(3) (k(7)) and CF(3)CD(OD)CF(3) (k(8)), are investigated as a function of temperature in the range of 268-378 K by laser photolysis-resonance fluorescence. To our knowledge, only the CF(3)CH(2)OH + Cl reaction has been previously studied from a kinetic point of view. The derived Arrhenius expressions obtained using our kinetic data are: k(4) = (1.79+/-0.17) x 10(-13) exp[(410+/-26)/T], k(5) = (1.20+/-0.11) x 10(-12) exp[(394+/-14)/T], k(6) = (2.32+/-0.18) x 10(-13) exp[-(740+/-12)/T], k(7) = (6.45+/-1.87) x 10(-13) exp[-(1136+/-94)/T] and k(8) = (4.19+/-1.09) x 10(-13) exp[-(1378+/-81)/T] (in units of cm(3) molecule(-1) s(-1) and where errors are +/-sigma). Moreover, a theoretical insight into the mechanisms of these reactions is pursued through ab initio Möller-Plesset second-order perturbation treatment calculations with the 6-311G** basis set. Optimized geometries are obtained for reagents, transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies are calculated at the quadratic configuration interaction with single, double and triple excitations [QCISD(T)] level to obtain an estimation of the activation energies. Finally, the rate constants are calculated through transition-state theory using Wigner's transmission coefficient in order to include the tunnelling-effect corrections.

Atmospheric Lifetimes and Global Warming Potentials of CF3CH2CH2OH and CF3(CH2)2CH2OH

“…This increase in k OH and k Cl with the length of the hydrocarbon chain has also been observed for the OH and Cl rate coefficients for partially fluorinated aldehydes CF 3 (CH 2 ) x CHO. [18] Regarding the degradation products of reactions (1) and (2), mechanistic studies carried out both in the absence and presence of NO x on the OH and Cl reactions with CF 3 CH 2 OH [6,25,26] and CF 3 CH 2 CH 2 OH [7][8][9] confirm that the main reaction pathway proceeds via hydrogen atom abstraction from the CH 2 group adjacent to the OH group, since the main primary product was the corresponding aldehyde. Theoretical studies recently performed by our group on the Cl-initiated reaction with CF 3 CH 2 OH [26] are consistent with the experimental observa- Table 2S of the Supporting Information.…”

An experimental and theoretical study on the reaction of Cl with CF3CF2CH2OH

“…A considerable difference is observed in the pre-exponential factors and E a values. This discrepancy in E a and A between low-and high-pressure kinetic experiments was already reported for the CF 3 CH 2 OH þ Cl reaction and was attributed to a difference in the reaction mechanism [15].…”

“…To make this secondary reaction negligible, an oxygen concentration ranging between 9 � 10 15 Figure 2, showing in all cases a good linearity.…”

“…In the present study, the Pulsed Laser Photolysis -Resonance Fluorescence (PLP-RF) technique was employed to determine the rate coefficients (k) for the CF 3 CF 2 CH 2 OH þ Cl reaction within the atmospheric pressure range of 50-200 Torr for the first time and as a function of temperature (268-377 K). This work is an extension of a recent study carried out in our laboratory on the reactions of Cl with CF 3 CH 2 OH and CF 3 CH(OH)CF 3 [15]. Additionally, the first step of the CF 3 CF 2 CH 2 OH þ Cl reaction was theoretically investigated in order to determine the most favourable reaction pathway in energy terms.…”

Contribution of the Atmospheric Chlorine Reactions to the Degradation of Greenhouse Gases: CFCs Substitutes

“…This effect can be observed in our calculation over the HFE-7500 where the RE increase around 28% whether we include the 0-900 cm -1 interval in the RE calculation, 0.55 vs 0.44 W m -2 ppbv -1 . Apart from the used on the prediction of radiative properties of molecules, computational techniques have successfully been used to establish reaction pathway in chemical mechanisms along with the predictions of atmospheric kinetic rates and hence lifetimes with relatively good accuracy [see for example : Rodríguez et al, 2010;Garzón et al, 2010]. Fig.…”