Photochemistry of CF3(CH2)2CHO 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 ; Jose.Albaladejo@uclm.es
- 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 CF3(CH2)2CHO. Firstly, the wavelength and temperature dependence of the UV absorption cross sections, 蟽位, 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 蟽位 = 283, 291 nm at 323 K is ca. 22%larger than those at 269 K. Secondly, the pulsed laser photolysis of a stationary mixture of CF3(CH2)2CHO/cyclohexane (OH-scavenger)/air or N2 was carried out at 308 nm. On-line Fourier transform infrared (FTIR) spectroscopy was employed to monitor the decay of CF3(CH2)2CHO and to obtain the photolysis quantum yield, 桅位 = 308 nm, 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 桅位 = 308 nm can be described by a Stern-Volmer relationship. Photodissociation of CF3(CH2)2CHO at 308 nm can produce HCO and CF3(CH2)2 radicals , CF3CH2CH3 and CO and CF3(CH2)2CO radicals and H atoms . HCO radicals are rapidly converted into CO in the presence of O2. Formation of CF3CH2CHO and CF3CH2CH2OH evidences the importance of secondary chemistry involving CF3(CH2)2 radicals formed in channel . Further photodegradation of CF3CH2CHO yields mainly CF3CHO. Small quantities of HC(O)OH were also detected. CF3(CH2)2C(O)OH was only observed in the absence of OH-scavenger, implying that formation of CF3(CH2)2CO radicals in channel is not an important photolysis pathway. Consequently, photodissociation of CF3(CH2)2CHO in the actinic region is a source of shorter fluorinated oxygenated compounds, but it is not expected to be a source of fluorinated acids.