Search

Perfluoro-n-propane, perfluorocyclobutane, perfluoro-n-butane, and perfluoro-n-pentane are non-ozone-depleting industrial alternatives to chlorofluorocarbons and hydrochlorofluorocarbons. However, these perfluoroalkanes have significant band strength in the atmospheric window from 800 to 1200 cm−1. Coupled with their millennial-scale atmospheric lifetimes, they can lead to significant long-term global warming. Infrared spectra are required to quantify the climate impacts. This work provides a set of high-temperature infrared absorption cross-sections in the range 298–350 K at 0.1 cm−1 resolution from 515 to 1500 cm−1 for each compound. Our cross-sections generally agree with literature measurements except for perfluoro-n-pentane. We use density functional theory to calculate the absorption cross-sections from 0 to 515 cm−1 using the B3LYP functional and several basis sets. The 6-31G(d,p) basis set provides the best results for linear perfluoroalkanes, while the def2-TZVP basis set provides the best results for cyclic perfluoroalkanes. Using experimental cross-sections, we calculate the radiative efficiency and global warming potential for each compound, utilizing the Pinnock curve from Shine and Myhre (2020) and atmospheric lifetimes from Hodnebrog et al. (2020). These quantities are found to be independent of temperature. The average 100-year global warming potential derived from all cross-sections is 9,610±1,260, 10,800±1,420, 10,100±1,330, and 9,380±1,230 for perfluoro-n-propane, perfluorocyclobutane, perfluoro-n-butane, and perfluoro-n-pentane, respectively. Combining the data in this work with our previous measurements reveals that the global warming potential for perfluoroalkanes with an increasing number of C F bonds depends on the ratio of radiative efficiency to molecular weight. [Display omitted] • Measured n-C 3 F 8 , n-C 4 F 10 , and n-C 5 F 12 cross-sections from 515–1500 cm−1 and 298–350 K. • Improved n-C 5 F 12 cross-sections compared to literature using a 99% pure sample. • Determined conformer populations for all compounds using density functional theory. • Investigated band strength and climate metrics trends with an increasing number of C F bonds. • Showed temperature independence of integrated cross-sections and climate metrics. [ABSTRACT FROM AUTHOR]

HFC-43-10mee (C 5 H 2 F 10 ) is a substitute for CFC-113, HCFC-141b and methyl chloroform, as well as an alternative to perfluorocarbons with high radiative efficiencies. Recent observations have shown that the global mean tropospheric abundance of HFC-43-10mee has increased steadily from the 1990s to reach 0.211 ppt in 2012. To date, the emission of this compound is not regulated. The radiative efficiency (RE) of HFC-43-10mee has recently been re-evaluated at 0.42 W m −2 ppb −1 , giving a 100-year time horizon global warming potential (GWP 100 ) of 1650. However, the initial RE, from which the new values were derived, originated from an unpublished source. We calculated a new RE of 0.36 W m −2 ppb −1 and a GWP 100 of 1410 from laboratory absorption cross-section spectra of a pure vapour of HFC-43-10mee. Acquisitions were performed in the 550–3500 cm −1 spectral range using Fourier transform spectroscopy. The results were compared with the broadened spectra from the Pacific Northwest National Laboratory (PNNL) database and with theoretical calculations using density functional theory. [ABSTRACT FROM AUTHOR]

Perfluoro-n-hexane and perfluoro-2-methylpentane are fully fluorinated alkanes used as non-ozone-depleting alternatives to chlorofluorocarbons and hydrochlorofluorocarbons. These compounds are long-lived and potent greenhouse gases due to their strong C F bonds and infrared absorption in the atmospheric window. Infrared absorption cross-sections are required to quantify the climate impact of these compounds via the radiative efficiency and global warming potential. To our knowledge, there are only two experimental measurements for perfluoro-n-hexane, and there are no experimental measurements for perfluoro-2-methylpentane in the infrared. In this work, we provide a set of absorption cross-sections in the range 515–1500 cm−1, at 0.1 cm−1 resolution from 298 to 350 K for each compound. We calculate the absorption cross-section between 0 and 515 cm−1 using density functional theory with various basis sets. The 6-31,G(d,p) basis set with the B3LYP functional is found to provide the best results. Using both measurements and calculations combined, we calculate the radiative efficiency and global warming potential for each compound. No significant temperature dependence was observed in these quantities. The average radiative efficiency derived from all cross-sections is 0.48 ± 0.06 W m−2 ppbv−1 for perfluoro-n-hexane and 0.46 ± 0.06 W m−2 ppbv−1 for perfluoro-2-methylpentane. The average 100-year global warming potential derived from all cross-sections is 9590 ± 1260 for perfluoro-n-hexane and 9220 ± 1210 for perfluoro-2-methylpentane. [Display omitted] • Obtained first measurements of the cross-sections of i C 6 F 14 from 515 to 1500 cm−1. • Measured cross-sections of n C 6 F 14 and confirmed the peak at 1255 cm−1. • Performed DFT calculations for all major C 6 F 14 conformers and determined their populations. • Derived global warming potentials of 9590 ± 1260 and 9220 ± 1210 for n C 6 F 14 and i C 6 F 14. • Showed temperature independence of integrated cross-sections and climate metrics. [ABSTRACT FROM AUTHOR]

Cross-sections of perfluorotributylamine (PFTBA) were derived from Fourier transform spectroscopy at 570–3400 cm −1 with a resolution of 0.1 cm −1 over a temperature range of 298–344 K. These results were compared to theoretical density functional theory (DFT) calculations and to previous measurements of PFTBA made at room temperature. DFT calculations were performed using the B3LYP method and the 6-311G(d,p) basis set. We find good agreement between our experimentally derived results, DFT calculations, and previously published data. No significant temperature dependence in the PFTBA cross-sections was observed for the temperature range studied. We calculate an average integrated band strength of 7.81 × 10 −16 cm/molecule for PFTBA over the spectral range studied. Radiative efficiencies (RE) and global warming potentials (GWP) for PFTBA were also derived. The calculated radiative efficiencies show no dependence on temperature and agree with prior publications. We find an average RE of 0.77 Wm −2 ppbv −1 and a range of GWP from 6874 to 7571 depending on the lifetime used. Our findings are consistent with previous studies and increase our confidence in the value of the GWP of PFTBA. [ABSTRACT FROM AUTHOR]

Perfluoroalkanes are fully fluorinated greenhouse gases. These compounds are chemically inert due to their C–F bonds and therefore have atmospheric lifetimes of thousands of years. Although regulated under the Kyoto Protocol, atmospheric concentrations of perfluoroalkanes have continued to increase since 1997. To quantify the climate impact of perfluoro-n-heptane and perfluoro-n-octane, spectral data are required to calculate climate metrics such as the radiative efficiency and global warming potential. Experimental measurements are scarce for these compounds and are only available at 296 and 297 K. In this work, a set of absorption cross-sections is provided in the range 515–1500 cm−1 at 0.1 cm−1 resolution for nine temperatures between 300 and 350 K. There is general agreement between literature values and the absorption cross-sections and climate metrics measured in this work. These quantities do not show significant temperature dependence. The temperature averaged radiative efficiency is 0.50 ± 0.06 and 0.54 ± 0.07 Wm−2ppbv−1 for n–C 7 F 16 and n–C 8 F 18 , respectively. The temperature averaged 100-year global warming potential is 8738 ± 1149 for n–C 7 F 16 and 8392 ± 1103 for n–C 8 F 18. [Display omitted] • Infrared cross-sections for n–C 7 F 16 and n–C 8 F 18 measured from 300 to 350 K. • Cross-sections confirm literature values for the spectral peak at 1250 cm−1. • Radiative efficiency is 0.50 ± 0.06 and 0.54 ± 0.07 Wm−2ppbv−1 for n–C 7 F 16 and n–C 8 F 18. • 100-year global warming potential is 8738 ± 1149 for n–C 7 F 16 and 8392 ± 1103 for n–C 8 F 18. • Integrated cross-sections and climate metrics are temperature-independent over 300–350 K. [ABSTRACT FROM AUTHOR]

[Display omitted] Absorption cross-sections for the 5th (6 ← 0) and 6th (7 ← 0) OH overtones for gas-phase methanol, ethanol, and isopropanol were measured using a slow flow cell and Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy (IBBCEAS). Measurements were performed in two wavelength regions, 447–457 nm, and 508–518 nm, using two different instruments. The experimental results are consistent with previous computational predictions of the excitation energies for these transitions. Treating the OH stretch as a local mode allowed for calculation of the fundamental vibrational frequency (ω e), anharmonicity constant (ω e x e), and the vertical dissociation energy (VDE) for each alcohol studied. The fundamental vibrational frequency is 3848 ± 18 cm−1, 3807 ± 55 cm−1, and 3813 ± 63 cm−1 for methanol, ethanol, and isopropanol, respectively. The anharmonicity constant was measured to be 84.8 ± 2.1 cm−1, 80.2 ± 5.9 cm−1, and 84.4 ± 6.8 cm−1 for methanol, ethanol, and isopropanol, respectively. The OH vertical dissociation energy was measured to be 499.4 ± 18.4 kJ/mol, 518.0 ± 56.7 kJ/mol, and 492.7 ± 59.9 kJ/mol. The spectroscopically measured values are compared to thermodynamically measured OH bond dissociation energies. The observed differences in previous measurements of the bond dissociation energies compared to the values reported herein can be explained due to the difference between vertical dissociation energies and bond dissociation energies. If the OH overtone stretching mode is excited in methanol to either the 5th or 6th overtone, the bimolecular reaction between methanol and O 2 becomes thermodynamically feasible and could contribute to formation of methoxy and HO 2 radical under the proper combination of pressure and temperature. [ABSTRACT FROM AUTHOR]

Mid-IR absorption cross-sections are measured for methane, ethane, ethylene and methanol over 2800–3400 cm −1 (2.9–3.6 μm) spectral region. Measurements are carried out using a Fourier-Transform-Infrared (FTIR) spectrometer with temperatures ranging 296–1100 K and pressures near atmospheric. As temperature increases, the peak cross-sections decrease but the wings of the bands increase as higher rotational lines appear. Integrated band intensity is also calculated over the measured spectral region and is found to be a very weak function of temperature. The absorption cross-sections of the relatively small fuels studied here show dependence on the bath gas. This effect is investigated by studying the variation of absorption cross-sections at 3.392 μm using a HeNe laser in mixtures of fuel and nitrogen, argon, or helium. Mixtures of fuel with He have the highest value of absorption cross-sections followed by Ar and N 2 . Molecules with narrow absorption lines, such as methane and methanol, show strong dependence on bath gas than molecules with relatively broader absorption features i.e. ethane and ethylene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigation of HFE-347pcf2 (1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether). • Acquisition of experimental absorption cross sections in the 550–3500 cm−1 range. • Extension of the spectrum in the low wavenumbers by theoretical simulations. • A radiative efficiency of 0.46 W m−2 ppb−1 and a 100-year global warming potential of 980 have been calculated. Composite absorption cross-sections of the hydrofluoroether HFE-347pcf2 (CAS number 406-78-0) have been determined from experimental and theoretical data. The experimental cross-sections have been used as a gauge to evaluate the accuracy of computational data obtained from different density functional theory methods. The B3LYP functional with a small 6-31G(d) basis set was found to provide the best results. A simulated spectrum was added to our experimental data to calculate the radiative efficiency and global warming potential of the molecule over the entire atmospheric spectral window. We found a radiative efficiency of 0.46 Wm−2ppb−1 and a 100-year global warming potential of 980. [ABSTRACT FROM AUTHOR]

• Experimental absorption cross‐sections of HFE‐356mec3 have been acquired. • Results have been compared with density functional theory and ab initio methods. • The lifetime‐corrected radiative efficiency was found to be 0.31 W.m−2 ppb−1. • This leads to a 100‐year time horizon global warming potential of 260. Experimental absorption cross-section spectra of HFE-356mec3 (CH 3 OCF 2 CHFCF 3) have been acquired at three temperatures and at a resolution of 0.1 cm−1 over the spectral range 550–3500 cm−1. The results have been completed with theoretical calculations using density functional theory and ab initio methods at different levels of theory. A lifetime-corrected radiative efficiency of 0.31 Wm−2ppb−1 was obtained, leading to a 100-year time horizon global warming potential of 260 using an atmospheric lifetime of 2.5 years. [ABSTRACT FROM AUTHOR]