Prediction of radiative forcing values for hydrofluoroethers using density functional theory methods

Abstract

1] In this work, we use computational chemistry at the B3LYP/6-31g* level of theory combined with Pinnock's cloudy sky instantaneous radiative transfer model to predict radiative forcing for hydrofluoroether compounds. We validate our predictive ability using the 27 values of cloudy sky radiative forcing reported in the literature before populating a database of 25 other hydrofluoroethers where no radiative forcing data is available. These additional compounds were selected because kinetic data are available for them and one could predict global warming potentials using the work reported here.

A group increment scheme for infrared absorption intensities of greenhouse gases

“…In all of these models, the coefficients increase as more fluorines are added to a terminal or inner carbon. This is in agreement with previous studies, 8,9 which show that an increase in carbon-fluorine bonds results in a nonlinear increase in intensity for absorption within the IRW, and also with the observations of Blowers et al 15,16 Also, the coefficients for the groups containing oxygen are higher than the coefficients of the equivalent non-oxygenated groups. This agrees with observations made previously that fluorinated carbons situated next to an oxygen result in a larger absorption in the IRW or a larger radiative efficiency.…”

“…This in combination with the carbon-fluorine vibrational stretch, which also occurs within the atmospheric IRW, makes perfluoroethers (PFEs) and HFEs very effective greenhouse gases. 8,9,12,[14][15][16][17][18] For fluorinated hydrocarbons and ethers, molecular structure greatly impacts its ability to absorb IR radiation. 9 It has been shown that by strategic distribution of fluorine atoms along the carbon framework, the infrared radiation absorption capacity can be reduced by a factor of two.…”

Design strategies to minimize the radiative efficiency of global warming molecules

“…While previous studies also noted some of these structure relationships for HFEs (11,15), our previous study (8) explained why this occurs using fundamental molecular properties, and thus we have extended these concepts to the other classes of compounds studied here. The current study is not meant to be an exhaustive survey of all molecules or even all classes of molecules that might be used in industrial applications, but rather it is meant to demonstrate how use of the concepts developed in our earlier study can be used to develop design strategies to engineer molecules with as small a radiative efficiency as possible.…”

“…The fact that perfluorinated ethers possess a larger radiative efficiency compared to the analogous perfluorocarbon has been known Table 1. BD and DD (both atomic units), harmonic vibrational frequencies (cm −1 ), IR intensities (km mol −1 ), total IR intensity, and IR intensity within the IR window for six perfluorinated molecules representative of six classes of global warming molecules (10,11,14,15), but the data in Table 1 show that this is for three main reasons: first, the C─F bond dipole is larger for CF 3 OCF 3 compared to CF 3 CF 3 , leading to larger IR intensities for the C-F stretches; second, the C─O bond dipole is very large, leading to large IR intensities for the C-O stretches, which fall into the IR window region (there is significant mixing between the C-O and C-F stretches, but a total energy distribution analysis shows that the bands at 1,205 and 1;301 cm −1 are mainly C-O stretches; see the SI Appendix); and third, because of the reduced symmetry in CF 3 OCF 3 compared to CF 3 CF 3 , there are four C-F stretching modes that have significant intensity, though the fourth-most intense mode at 972 cm −1 has an IR intensity of only 94 km mol −1 , compared with 755 km mol −1 for the most intense C-F stretch (note that this third component, symmetry, will not necessarily be present in larger perfluorcarbons where the molecular symmetry is lowered relative to CF 3 CF 3 ). Hence perfluorinated ethers possess enhanced IR intensities for the C-F stretches relative to perfluorocarbons, and they add two more C-O stretching modes with large IR intensities in the IRW.…”

An Environmentally Friendly Class of Fluoropolyether: α,ω-Dialkoxyfluoropolyethers

“…Therefore, considerable attention has been paid in recent years to perform both experimental and theoretical studies on atmospheric chemistry of HFEs. However, surprisingly, only relatively little information about DA-FPEs has been reported [36,37]. Since the only available data on DA-FPEs compounds are related to DM-FPEs with structure CH 3 O(CF 2 CF 2 O) n CH 3 that only contain the -(CF 2 CF 2 O)-units, the discussion has been focused prevalently on the atmospheric chemistry of these compounds.…”