Estimations of Global Warming Potentials from Computational Chemistry Calculations for CH₂F₂ and Other Fluorinated Methyl Species Verified by Comparison to Experiment

Abstract

In this work, the global warming potential (GWP) of methylene fluoride (CH(2)F(2)), or HFC-32, is estimated through computational chemistry methods. We find our computational chemistry approach reproduces well all phenomena important for predicting global warming potentials. Geometries predicted using the B3LYP/6-311g** method were in good agreement with experiment, although some other computational methods performed slightly better. Frequencies needed for both partition function calculations in transition-state theory and infrared intensities needed for radiative forcing estimates agreed well with experiment compared to other computational methods. A modified CBS-RAD method used to obtain energies led to superior results to all other previous heat of reaction estimates and most barrier height calculations when the B3LYP/6-311g** optimized geometry was used as the base structure. Use of the small-curvature tunneling correction and a hindered rotor treatment where appropriate led to accurate reaction rate constants and radiative forcing estimates without requiring any experimental data. Atmospheric lifetimes from theory at 277 K were indistinguishable from experimental results, as were the final global warming potentials compared to experiment. This is the first time entirely computational methods have been applied to estimate a global warming potential for a chemical, and we have found the approach to be robust, inexpensive, and accurate compared to prior experimental results. This methodology was subsequently used to estimate GWPs for three additional species [methane (CH(4)); fluoromethane (CH(3)F), or HFC-41; and fluoroform (CHF(3)), or HFC-23], where estimations also compare favorably to experimental values.

Global warming potential estimates for the C<sub>1</sub>–C<sub>3</sub> hydrochlorofluorocarbons (HCFCs) included in the Kigali Amendment to the Montreal Protocol

“…More recently, tests of the B3LYP functional found good performance for frequency and intensity (Jiménez-Hoyos et al, 2008;Katsyuba et al, 2013). Some prior work where similar methods have been applied to the infrared absorption for molecules of atmospheric interest include studies of fluoromethanes (Blowers and Hollingshead, 2009), unsaturated hydrofluorocarbons (Papadimitriou and Burkholder, 2016;Papadimitriou et al, 2008b), perfluorocarbons (Bravo et al, 2010), chloromethanes (Wallington et al, 2016), SO 2 F 2 (Papadimitriou et al, 2008a), permethylsiloxanes (Bernard et al, 2017), and large survey studies such as by Kazakov et al (2012) and Betowski et al (2015) to name a few. Halls and Schlegel noted that real spectra may exhibit the influences of resonances, intensity sharing, and largeamplitude anharmonic modes.…”

Disorder of Hydrofluorocarbon Molecules Entrapped in the Water Cages of Structure I Clathrate Hydrate

“…19 FNMR spectroscopy measurements were also performed for comparison with the cage occupancies of HFC hydrates analyzed by PXRD (see Figure S5 in the Supporting Information). As ar esult, the CH 3 Fm olecules almostf ully occupy both 5 12 and 5 12 6 2 cages.…”

“…[16][17][18] AlthoughH FCs do not have ozone depletion potential, their globalw arming potentiali sm uch greater than those of CO 2 and CH 4 . [19,20] Understanding the stabilities of these clathrate hydrates may also be useful for hydrate-based technologieso ng as storagea nd/or gas separation, as well as cool energy storagea nd desalination. [21] Results and Discussion SimpleC H 3 F, CH 2 F 2 ,C HF 3 ,a nd CF 4 hydrates formed cubic sI hydrates similar to that of CH 4 hydrate, as expected.…”

Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report)

“…They compared their data obtained with available literature data and described how molecular structure can be changed to reduce the warming effect. Recently, Blowers and Hollingshead [203] used B3LYP/6-311G(d,p) for initial geometry optimization of fluoromethanes and methane and reported that the CBS-RAD composite energy method should be a better procedure to obtain energies. They successfully applied purely computational methods, for the first time, to correlate the computed and experimental GWPs of methyl fluoride species.…”

“…(7) GWP of gaseous species can be computed with the theoretical methods proposed by Blowers and Hollingshead [203].…”