VUV photon induced fluorescence study of SF<sub>5</sub>CF<sub>3</sub>

a b s t r a c tUsing two complementary experimental methods, we have measured partial (mass-resolved) crosssections for dissociative electron attachment to the molecule trifluoromethyl sulfurpentafluoride (SF 5 CF 3 ) at the gas temperature T G = 300 K over a broad range of electron energies (E = 0.001-12 eV). The absolute scale for these cross-sections was obtained with reference to the thermal (T = 300 K) rate coefficient for anion formation (8.0(3) × 10 −8 cm 3 s −1 ). Below 1 eV, SF 5 − is the dominant product anion and formed through the lowest anion state which cuts the neutral SF 5 CF 3 potential close to the S-C equilibrium distance. The highly resolved laser photoelectron attachment data exhibit a downward Wigner cusp at 86 meV, indicating that the 4 (a 1 ) vibrational mode is important for the primary attachment dynamics. Both SF 5 − and F − anions are formed with similar yields through the first excited resonance located near 3.6 eV. Towards higher energies, the anions CF 3 − , SF 4 − , and SF 3 − are also produced. Summation of the partial cross-sections yields a total absolute cross-section for anion formation over the energy range 0.001-12 eV. This is used to calculate the dependence of the rate coefficient for dissociative electron attachment over a broad range of electron temperatures for the fixed gas temperature T G = 300 K; good agreement is found between the calculated values and those obtained in a drift tube experiment. In addition to the experimental work, semiempirical R-matrix calculations have been carried out for the energy dependence of the cross-section for SF 5 − formation. The experimental findings are semi-quantitatively recovered.

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Chapter 3: Trifluoromethyl Sulphur Pentafluoride, SF5CF3: Atmospheric Chemistry and Its Environmental Importance via the Greenhouse Effect

Tuckett

2006

Fluorine and the Environment - Atmospheric Chemistry, Emissions, &Amp; Lithosphere

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Advances in Fluorine Science (2006) 1, chapter 3 (pp. 89-129) (Elsevier, ISBN 0-444-52811-3) Fluorine and the Environment : atmospheric chemistry, emissions and lithosphere DOI: 10.1016/S1872-0358(06) This is the author's version of a work that was accepted for publication in Advances in Fluorine Science.Changes resulting from the publishing process, such as editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. A definitive version was subsequently published in the reference given above. The DOI number of the final paper is also given above. highest per molecule radiative forcing of any greenhouse pollutant, and the value of its global warming potential is only exceeded by that of SF 6 . Using tunable vacuum-UV radiation from a synchrotron and coincidence spectroscopy, the strength of the central S−C bond in SF 5 CF 3 is determined to be 3.86 ± 0.45 eV or 372 ± 43 kJ mol -1 , and this molecule is very unlikely to be removed from the earth's atmosphere by UV photolysis in the stratosphere. Complementary laboratory-based experiments have shown that the main sink route of this greenhouse gas is low-energy electron attachment in the mesosphere, with Lyman-α photodissociation at 121.6 nm being only a minor channel. By comparison with data for SF 6 , the lifetime of SF 5 CF 3 in the earth's atmosphere is estimated to be ca. 1000 years. The principal reason for the current low level of concern about the impact of SF 5 CF 3 on our environment is that the concentration levels are still very low, at the sub parts per trilllion level. The high growth rate of ca. 6% per annum, however, should cause concern for policymakers.

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VUV photon induced fluorescence study of SF₅CF₃

Cited by 5 publications

References 36 publications

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Highly resolved absolute cross-sections for dissociative electron attachment to SF5CF3

Chapter 3: Trifluoromethyl Sulphur Pentafluoride, SF5CF3: Atmospheric Chemistry and Its Environmental Importance via the Greenhouse Effect

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VUV photon induced fluorescence study of SF5CF3

Cited by 5 publications

References 36 publications

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Vacuum Ultraviolet Negative Photoion Spectroscopy of SF6, CF4 and SF5CF3

Highly resolved absolute cross-sections for dissociative electron attachment to SF5CF3

Chapter 3: Trifluoromethyl Sulphur Pentafluoride, SF5CF3: Atmospheric Chemistry and Its Environmental Importance via the Greenhouse Effect

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VUV photon induced fluorescence study of SF₅CF₃