Dissociative Photoionization of Diethyl Ethe
Poster Number
20
Introduction/Abstract
Ever since ozone depletion was correlated to chlorofluorocarbon (CFC) consumption by Rowland and Molina1 and the Montreal Protocol was passed in 1987, CFCs have been slowly phased out. Since 1974, several research confirmed that CFC usage is directly linked to ozone depletion and global warming. In fact many ozone depleting substances (ODSs) are compared to CFCs in how much ozone they deplete by setting the ozone depleting potential (ODP) of CFCl3 to 1.0. At the same time, CFCs are also potential contributors to global warming, which effect can be described as global warming potential (GWP).
Purpose
Unfortunately, there are still cases in which CFCs must be used, because of a lack of alternatives. Consequently, accurate thermochemical information on CFCs is important for atmospheric models. Imaging Photoelectron Photoion (iPEPICO) Spectroscopy has the ability to energy select photoions by monochromatic vacuum ultraviolet (VUV) photoionization and by detecting photoions in coincidence with threshold photoelectrons. It can provide the necessary accuracy for thermochemical networks.
Method
The dissociative photoionization of three chlorofluorocarbons, CF3Cl, CF2Cl2 and CFCl3 (CFC-13, CFC-12 and CFC-11) was studied by Imaging Photoelectron Photoion Coincidence (iPEPICO) Spectroscopy. The molecular ions were prepared by vacuum ultraviolet photoionization and their lowest energy dissociation channel was studied, where all three energy selected molecular ions lose a chlorine atom.
Results
At higher photon energies, CFC-13 and CFC-12 also exhibit a fluorine-loss dissociation channel, parallel with chlorine loss. Zero-kelvin appearance energies were determined for all five dissociation processes by modeling the experimental data. In the case of CFC-13, the effect of a shallow potential energy well only slightly influenced the breakdown curve (fractional ion abundance as the function of photon energy) and the whole breakdown curve was used to determine an accurate 0-K onset and the adiabatic ionization energy. In CFC-12, the breakdown curve exhibited wide oscillations coinciding with the peaks in the threshold photoelectron spectrum and the slope of the curve indicated that the potential energy well is again shallower than the width of the room-temperature energy distribution of the neutral precursor. For this system and also for CFC-11, the 0-K onset was determined from the disappearance point of the parent ion signal. The second, fluorine-loss dissociation was modeled using rigid activated complex RRKM theory to take the competitive shift into account when determining the appearance energy of the [M–F]+ daughter ions. The 0 K onset energies for the Cl-loss dissociation for CF3Cl, CF2Cl2, and CFCl3 were 12.802 ± 0.003 eV, 12.029 ± 0.010 eV, and 11.622 ± 0.006 eV, respectively. The 0 K onset energies for the F-loss dissociation for CF3Cl and CF2Cl2 were 13.69 ± 0.10 eV and 13.92 ± 0.10 eV respectively.
Significance
Accurate thermochemical information on CFCs is important for atmospheric models.
Location
DeRosa University Center, Stockton campus, University of the Pacific
Format
Poster Presentation
Dissociative Photoionization of Diethyl Ethe
DeRosa University Center, Stockton campus, University of the Pacific
Ever since ozone depletion was correlated to chlorofluorocarbon (CFC) consumption by Rowland and Molina1 and the Montreal Protocol was passed in 1987, CFCs have been slowly phased out. Since 1974, several research confirmed that CFC usage is directly linked to ozone depletion and global warming. In fact many ozone depleting substances (ODSs) are compared to CFCs in how much ozone they deplete by setting the ozone depleting potential (ODP) of CFCl3 to 1.0. At the same time, CFCs are also potential contributors to global warming, which effect can be described as global warming potential (GWP).
