NASA - National Aeronautics and Space Administration

Rate constants for the gas-phase reactions of OH radicals with three partially halogenated alkanes, CH₃Cl (k_MC), CHFClCFCl₂ (k_122a), and CH₂FCFCl₂ (k_132c), were measured using a discharge flow−electron paramagnetic resonance technique over the temperature range from 298 to 460 K. The temperature dependences of the rate constants can be represented by the expressions k_MC(298−460 K) = (3.09 ± 0.94) × 10⁻¹² exp[−(1411 ± 85)/T] cm³molecule⁻¹s⁻¹, k_122a(298−460 K) = (1.26 ± 0.24) × 10⁻¹² exp[−(1298 ± 66)/T] cm³molecule⁻¹s⁻¹, and k_132c(298− 370 K) = (8.1 ± 2.2) × 10⁻¹³ exp[−(1247 ± 89)/T] cm³molecule⁻¹s⁻¹. The atmospheric lifetimes of CH₃Cl, CHFClCFCl₂, and CH₂FCFCl₂ due to their reaction with OH were estimated to be 1.6, 3.5, and 4.5 years, respectively. The UV absorption cross sections of halogenated ethanes, CHFClCFCl₂, and CH₂FCFCl₂, were measured at T = 295 K between 190 and 240 nm, as were those for CHCl₂CF₂Cl (HCFC-122), CHCl₂CF₃ (HCFC-123), CHFClCF₂Cl (HCFC-123a), and CH₃CFCl₂ (HCFC141b). The atmospheric lifetimes due to stratospheric photolysis were also estimated.