Atmospheric Chemistry of CF3CF2CHO: Absorption Cross Sections in the UV and IR Regions, Photolysis at 308 nm, and Gas-Phase Reaction with OH Radicals (T = 263–358 K)

Abstract

The relative importance in the atmosphere of UV photolysis of perfluoropropionaldehyde, CF3CF2CHO, and reaction with hydroxyl (OH) radicals has been investigated in this work. First, the forbidden n → π* transition of the carbonyl chromophore was characterized between 230 and 380 nm as a function of temperature (269–298 K) and UV absorption cross sections, σλ, were determined in those ranges. In addition, IR absorption cross sections were determined between 4000 and 500 cm–1. Pulsed laser photolysis (PLP) of CF3CF2CHO coupled to Fourier transform infrared (FTIR) was employed to determine the overall photolysis quantum yield, Φλ, at 308 nm and 298 K. Φλ=308 nm was pressure dependent, ranging from (0.94 ± 0.14) at 75 Torr to (0.30 ± 0.01) at 760 Torr. This dependence is characterized by the Stern–Volmer parameters Φ0λ=308 nm = (1.19 ± 0.34) and KSV = (1.22 ± 0.52) × 10(–19) cm3 molecule–1. End products of the photodissociation of CF3CF2CHO were measured and quantified by FTIR spectroscopy. Furthermore, the rate coefficients for the OH + CF3CF2CHO reaction, k1, were determined as a function of temperature (T = 263–358 K) by PLP-LIF. At room temperature the rate coefficient is k1(T = 298 K) = (5.57 ± 0.07) × 10(–13) cm3 molecule–1 s–1, whereas the temperature dependence is described by k1(T) = (2.56 ± 0.32) × 10(–12) exp{−(458 ± 36)/T} cm3 molecule–1 s–1. On the basis of our results, photolysis of CF3CF2CHO in the actinic region could be an important removal process for CF3CF2CHO in the atmosphere. The formation of the primary products in the UV photolysis of CF3CF2CHO is also discussed.