Photochemistry of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CHO in air: UV absorption cross sections between 230 and 340 nm and photolysis quantum yields at 308 nm
- 作者：M. Antiñ ; olo ; E. Jimé ; nez ; J. Albaladejo<sup> ; sup><sup>Jose.Albaladejo@uclm.essup>
- 关键词：Atmospheric photodegradation ; Fluorinated aldehyde ; Absorption cross sections ; Quantum yields ; Photoproducts
- 刊名：Journal of Photochemistry and Photobiology A ; Chemistry
- 出版年：2012
- 期刊代码：66_10106030
- 类别：ch
- 出版时间：1 March, 2012
- 卷：231
- 期：1
- 页码：33-40
- 文件大小：640 K
摘要
This work constitutes the first study on the photochemical degradation process of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CHO. Firstly, the wavelength and temperature dependence of the UV absorption cross sections, 蟽<sub>位sub>, was determined. The n 鈫?#xA0;蟺* electronic transition band of CO chromophore was characterized between 230 and 340 nm in the 269-323 K range. A hyperchromic effect was observed in the structured part of the band when the temperature decreases. Maximum 蟽<sub>位 = 283, 291 nmsub> at 323 K is ca. 22%larger than those at 269 K. Secondly, the pulsed laser photolysis of a stationary mixture of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CHO/cyclohexane (OH-scavenger)/air or N<sub>2sub> was carried out at 308 nm. On-line Fourier transform infrared (FTIR) spectroscopy was employed to monitor the decay of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CHO and to obtain the photolysis quantum yield, 桅<sub>位 = 308 nmsub>, as a function of total pressure (20.5-760 Torr). A slight curvature in the Stern-Volmer plot was observed at pressures lower than 75 Torr. At high pressures, the pressure dependence of 桅<sub>位 = 308 nmsub> can be described by a Stern-Volmer relationship. Photodissociation of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CHO at 308 nm can produce HCO and CF<sub>3sub>(CH<sub>2sub>)<sub>2sub> radicals , CF<sub>3sub>CH<sub>2sub>CH<sub>3sub> and CO and CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CO radicals and H atoms . HCO radicals are rapidly converted into CO in the presence of O<sub>2sub>. Formation of CF<sub>3sub>CH<sub>2sub>CHO and CF<sub>3sub>CH<sub>2sub>CH<sub>2sub>OH evidences the importance of secondary chemistry involving CF<sub>3sub>(CH<sub>2sub>)<sub>2sub> radicals formed in channel . Further photodegradation of CF<sub>3sub>CH<sub>2sub>CHO yields mainly CF<sub>3sub>CHO. Small quantities of HC(O)OH were also detected. CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>C(O)OH was only observed in the absence of OH-scavenger, implying that formation of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CO radicals in channel is not an important photolysis pathway. Consequently, photodissociation of CF<sub>3sub>(CH<sub>2sub>)<sub>2sub>CHO in the actinic region is a source of shorter fluorinated oxygenated compounds, but it is not expected to be a source of fluorinated acids.