Chemical kinetics of the reactions of the OH radical with several hydrochlorofluoropropanes
- Aerodyne Research Inc., Billerica, MA (United States)
The rate constants for the reaction of the OH radical with three hydrochlorofluorocarbons (HCFC-225ca, HCFC-225cb, and HCFC-243cc) have been measured as a function of temperature using the discharge flow technique. The reaction of these species with OH radicals in the troposphere is expected to determine their tropospheric lifetimes. Their tropospheric lifetimes, in turn, largely determine the extent of their role in stratospheric ozone depletion. The rate constants were measured in the temperature range 295-370 K, and the resulting Arrhenius plots (ln (k) vs 1/T) showed no curvature within the experimental uncertainties over this temperature range. Expressing the rate constants as k(T) = A exp[{minus}E/(RT)], the authors find A = (6.5 {+-} 1.3) x 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, E/R = 970 {+-} 115 K for HCFC-225ca; A = (3.9 {+-} 0.7) x 10{sup {minus}13} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, for HCFC-225cb; and A+(7.1{+-}2.8)x10{sup {minus}13}cm{sup 3}molecules{sup {minus}1}s{sup {minus}1}, E/R = 1690 {+-} 230 K for HCFC-243cc. The uncertainties in the rate constants calculated from the above expression are estimated to be {approximately} 10% for HCFC-225ca and HCFC-225cb and {approximately}15% for HCFC-243cc over the measured temperature range. Using thermochemical transition-state theory, the authors show that these Arrhenium parameters are consistent with those of analogous ethane based HCFCs. Surface reactions in the flow tube reactor prevented the direct measurement of rate constants for these reactions at temperatures below room temperature. However, using the reported Arrhenium parameters, the authors calculate the rate coefficients at 277 K, the weighted mean temperature of the troposphere, and derive tropospheric lifetimes for HCFC-225ca, -225cb, and -243cc of 4, 8, and 44 years, respectively.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 563387
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 1 Vol. 96; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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