The reaction kinetics of chlorine atoms with the hydrofluoroethers CHF2CF2OCH3 (1), CHF2CF2OCH2CH3 (2), CHF2CF2OCH2CF3 (3), CF3CHFCF2OCH3 (4), and CH2CHCH2OCF2CHF2 (5) were studied in the gas phase over the temperature range 273−363 K. The experiments were performed at very low pressures (<3 mTorr) in a molecular flow system equipped with a quadrupole mass spectrometer by monitoring both reactants. The proposed Arrhenius expressions for the studied reactions are (in cm3 molecule-1 s-1, 2σ uncertainties):  k 1 = (5.49 ± 1.51) × 10-12 exp(−928 ± 155/T), k 2 = (1.99 ± 0.12) × 10-12 exp(−36 ± 33/ T), k 3 = (1.95 ± 0.72) × 10-12 exp(−1616 ± 202/T), k 4 = (8.72 ± 2.93) × 10-12 exp(−1112 ± 186/T), and k 5 = (5.54 ± 1.96) × 10-13 exp(821 ± 214/T). The title reactions proceed via hydrogen atom metathesis, with the exception of the unsaturated CH2CHCH2OCF2CHF2 ether, where the Cl-atom addition pathway leading to CH2CHCl is also present. The C−H bond strengths in several hydrofluoroethers were calculated at the B3P86/6-311++G(3df,2p) level of theory, and they show an increase in the order −OCH(CH3)−H < −OCH(CF3)−H < −CH2OCH2−H < −CF2OCH2−H < −OCH2CH2−H < −OCF2CF2−H < −OCF2−H. Furthermore, their room-temperature rate coefficients correlate with the weakest C−H bond strengths in each molecule, according to the expression log(k, in cm3 molecule-1 s-1) = (23.6 ± 7.4) − (0.09 ± 0.02) × [C−H bond strength (in kJ mol-1)]. In addition, their vertical ionization potentials were calculated at the B3LYP/6-311++G(3df,2p) level of theory, and they also correlate with the room-temperature rate coefficients according to the expression log(k, in cm3 molecule-1 s-1) = (4.0 ± 1.7) − (1.42 ± 0.15) × [ionization potential (in eV)].

The absolute rate constants for the reactions of chlorine atoms with several hydrofluoroethers, CHF 2 OCHF 2 (1), CF 3 CH 2 OCH 3 (2), CF 3 CH 2 OCHF 2 (3), and CF 3 CH 2 OCH 2 CF 3 (4), were measured in the gas phase over the temperature range 273-363 K. The experiments were performed with a very low pressure reactor (VLPR) in a molecular flow system, where both reactants and products were simultaneously monitored with a quadrupole mass spectrometer. The absolute rate constants are given by the expressions (in cm 3 molecule -1 s -1 , 2σ uncertainties): k 1 ) (1.03 ( 0.19) × 10 -12 exp(-867 ( 106/T), k 2 ) (2.26 ( 0.20) × 10 -11 exp(0 ( 50/T), k 3 ) (3.84 ( 1.00) × 10 -12 exp(-1451 ( 147/T), and k 4 ) (4.03 ( 0.87) × 10 -12 exp(-680 ( 121/T). All reactions proceed via the abstraction of a hydrogen atom and lead to the formation of HCl. The C-H bond strengths of the fluoroethers under study were determined theoretically by ab initio calculations, using the 6-31G basis set, augmented by polarization and diffusion functions. Electron correlation was taken into account by second-order Møller-Plesset perturbation theory (MP2, frozen core). The theoretical results suggest that the C-H bond strengths are increasing in the order -OCH 2 -H < -OCH(CF 3 )-H < -OCF 2 -H. Furthermore, the calculated C-H bond strengths are correlated with the corresponding rate parameters for the reactions of Cl atoms with CF 3 CH 2 OCH 3 , CF 3 CH 2 OCH 2 CF 3 , and CHF 2 OCHF 2 , respectively.

The rate constants for the reactions of chlorine atoms with the complete series of the three bromomethanes CH 3 Br (1), CH 2 Br 2 (2), and CHBr 3 (3) were measured in a very low pressure reactor, employing a microwave discharge for the generation of Cl atoms with mass spectrometric detection of reactants and products. The experiments were performed in the temperature range 273-363 K and at total pressures ∼1 mTorr. The reactions proceed via hydrogen atom transfer leading to HCl product and the corresponding bromomethyl radicals. Their rate constant expressions are (in cm 3 molecule -1 s -1 ): k 1 ) (1.66 ( 0.14) × 10 -11 exp(-1072 ( 46/T), k 2 ) (0.84 ( 0.15) × 10 -11 exp(-911 ( 101/T), and k 3 ) (0.43 ( 0.11) × 10 -11 exp (-809 ( 142/T). The activation energy of the reaction decreases with additional bromine substitution, which is attributed to the gradual weakening of the corresponding C-H bond strength. Ab initio theoretical calculations performed at the MP2/6-31++G(2d,2p) level of theory suggest C-H bond strengths for CH 3 Br, CH 2 Br 2 , and CHBr 3 of 416.58, 407.03, and 396.60 kJ mol -1 , respectively. Reactions of Cl Atoms with Bromomethanes

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