| Autor: |
Mogelberg, T. E., Sehested, J., Tyndall, G. S., Orlando, J. J., Fracheboud, J.-M., Wallington, T. J. |
| Zdroj: |
The Journal of Physical Chemistry - Part A; April 10, 1997, Vol. 101 Issue: 15 p2828-2832, 5p |
| Abstrakt: |
An FTIR/environmental chamber technique was used to study the fate of the alkoxy radical CF3CF2CFHO formed in the atmospheric degradation of HFC-236cb (CF3CF2CFH2). Experiments were performed over the temperature range 228−296 K at 7.8−1000 Torr total pressure. Two reaction pathways are possible for CF3CF2CFHO radicals: reaction with oxygen, CF3CF2CFHO + O2 → CF3CF2C(O)F + HO2 (kO2) and decomposition via C−C bond scission, CF3CF2CFHO → CF3CF2 + HC(O)F (kd). CF3CF2CFHO radicals were produced by two reactions: the CF3CF2CFHO2 self-reaction and the CF3CF2CFHO2 + NO reaction. In the absence of NO at 800 Torr total pressure the rate constant ratio kd/kO2 was determined to be (%@mt;sys@%6.6%@sx@%-4.7%@be@%+16.3%@sxx@%%@mx@% ) × 1025 exp(−(3560 ± 295)/T) molecules cm-3. The pressure dependence of kd/kO2 was studied at 238 K and was well described by a Troe type expression using kd,0/kO2 = 30.8 ± 6.9 and kd,∞/kO2 = (2.31 ± 0.12) × 1019 molecules cm-3 where kd,0 and kd,∞ are the second- and first-order rate constants for decomposition in the low- and high-pressure limits, respectively. CF3CF2CFHO radicals formed in the CF3CF2CFHO2 + NO reaction undergo more C−C bond scission than those generated in the CF3CF2CFHO2 self-reaction. This is consistent with a significant fraction (%@mt;sys@%67%@sx@%-22%@be@%+19%@sxx@%%@mx@% %) of the alkoxy radicals being formed with sufficient internal energy to undergo prompt decomposition. Overall, we calculate that less than 1% of the CF3CF2CFH2 (HFC-236cb) released to the atmosphere degrades to form CF3CF2C(O)F while >99% gives CF3CF2 radicals and HC(O)F. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
|
