Photochemistry of CFb>3b>(CHb>2b>)b>2b>CHO in air: UV absorption cross sections between 230 and 340 nm and photolysis quantum yields at 308 nm

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• 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 CFb>3b>(CHb>2b>)b>2b>CHO. Firstly, the wavelength and temperature dependence of the UV absorption cross sections, 蟽b>位b>, 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b>位 = 283, 291 nmb> at 323 K is ca. 22%larger than those at 269 K. Secondly, the pulsed laser photolysis of a stationary mixture of CFb>3b>(CHb>2b>)b>2b>CHO/cyclohexane (OH-scavenger)/air or Nb>2b> was carried out at 308 nm. On-line Fourier transform infrared (FTIR) spectroscopy was employed to monitor the decay of CFb>3b>(CHb>2b>)b>2b>CHO and to obtain the photolysis quantum yield, 桅b>位 = 308 nmb>, 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b>位 = 308 nmb> can be described by a Stern-Volmer relationship. Photodissociation of CFb>3b>(CHb>2b>)b>2b>CHO at 308 nm can produce HCO and CFb>3b>(CHb>2b>)b>2b> radicals , CFb>3b>CHb>2b>CHb>3b> and CO and CFb>3b>(CHb>2b>)b>2b>CO radicals and H atoms . HCO radicals are rapidly converted into CO in the presence of Ob>2b>. Formation of CFb>3b>CHb>2b>CHO and CFb>3b>CHb>2b>CHb>2b>OH evidences the importance of secondary chemistry involving CFb>3b>(CHb>2b>)b>2b> radicals formed in channel . Further photodegradation of CFb>3b>CHb>2b>CHO yields mainly CFb>3b>CHO. Small quantities of HC(O)OH were also detected. CFb>3b>(CHb>2b>)b>2b>C(O)OH was only observed in the absence of OH-scavenger, implying that formation of CFb>3b>(CHb>2b>)b>2b>CO radicals in channel is not an important photolysis pathway. Consequently, photodissociation of CFb>3b>(CHb>2b>)b>2b>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.