title: CF3CF=CH2 and (Z)-CF3CF=CHF: temperature dependent OH rate coefficients and global warming potentials.
abstract: Rate coefficients over the temperature range 206-380 K are reported for the gas-phase reaction of OH radicals with 2,3,3,3-tetrafluoropropene (CF(3)CF=CH(2)), k(1)(T), and 1,2,3,3,3-pentafluoropropene ((Z)-CF(3)CF=CHF), k(2)(T), which are major components in proposed substitutes for HFC-134a (CF(3)CFH(2)) in mobile air-conditioning units. Rate coefficients were measured under pseudo-first-order conditions in OH using pulsed-laser photolysis to produce OH and laser-induced fluorescence to detect it. Rate coefficients were found to be independent of pressure between 25 and 600 Torr (He, N(2)). For CF(3)CF=CH(2), the rate coefficients, within the measurement uncertainty, are given by the Arrhenius expression k(1)(T)=(1.26+/-0.11) x 10(-12) exp[(-35+/-10)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K)=(1.12+/-0.09) x 10(-12) cm(3) molecule(-1) s(-1). For (Z)-CF(3)CF=CHF, the rate coefficients are given by the non-Arrhenius expression k(2)(T)=(1.6+/-0.2) x 10(-18)T(2) exp[(655+/-50)/T] cm(3) molecule(-1) s(-1) where k(2)(296 K)=(1.29+/-0.06) x 10(-12) cm(3) molecule(-1) s(-1). Over the temperature range most relevant to the atmosphere, 200-300 K, the Arrhenius expression k(2)(T)=(7.30+/-0.7) x 10(-13) exp[(165+/-20)/T] cm(3) molecule(-1) s(-1) reproduces the measured rate coefficients very well and can be used in atmospheric model calculations. The quoted uncertainties in the rate coefficients are 2sigma (95% confidence interval) and include estimated systematic errors. The global warming potentials for CF(3)CF=CH(2) and (Z)-CF(3)CF=CHF were calculated to be <4.4 and <3.6, respectively, for the 100 year time horizon using infrared absorption cross sections measured in this work, and atmospheric lifetimes of 12 and 10 days that are based solely on OH reactive loss.
authors.affiliation: Earth System Research Laboratory, Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, Colorado 80305-3328, U S A.
authors.forename: Vassileios C
authors.initials: VC
authors.lastname: Papadimitriou
authors.forename: Ranajit K
authors.initials: RK
authors.lastname: Talukdar
authors.forename: R W
authors.initials: RW
authors.lastname: Portmann
authors.forename: A R
authors.initials: AR
authors.lastname: Ravishankara
authors.forename: James B
authors.initials: JB
authors.lastname: Burkholder
mesh_terms: D005466:Fluorocarbons / Q000737:chemistry* / Q000528:radiation effects; D017752:Greenhouse Effect; D017665:Hydroxyl Radical / Q000737:chemistry*; D007834:Lasers; D010782:Photolysis; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation / Q000379:methods; D013237:Stereoisomerism; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays; D006845:Hydrocarbons, Fluorinated
chemical_list: D005466:Fluorocarbons; D017665:Hydroxyl Radical; C528199:1,2,3,3,3-pentafluoropropene; C528198:2,3,3,3-tetrafluoropropene; D006845:Hydrocarbons, Fluorinated