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The Journal of chemical physics, 2009-05, Vol.130 (19), p.194302-194302-11
2009
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Autor(en) / Beteiligte
Titel
Vacuum-UV negative photoion spectroscopy of CF 3 Cl , CF 3 Br , and CF 3 I
Ist Teil von
  • The Journal of chemical physics, 2009-05, Vol.130 (19), p.194302-194302-11
Ort / Verlag
American Institute of Physics
Erscheinungsjahr
2009
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
  • Using synchrotron radiation, negative ions are detected by mass spectrometry following vacuum-UV photoexcitation of trifluorochloromethane ( CF 3 Cl ) , trifluorobromomethane ( CF 3 Br ) , and trifluoroiodomethane ( CF 3 I ) . The anions F − , X − , F 2 − , F X − , CF − , CF 2 − , and CF 3 − are observed from all three molecules, where X = Cl , Br, or I, and their ion yields recorded in the range of 8-35 eV. With the exception of Br − and I − , the anions observed show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation. Dissociative electron attachment, following photoionization of CF 3 Br and CF 3 I as the source of low-energy electrons, is shown to dominate the observed Br − and I − signals, respectively. Cross sections for ion-pair formation are put onto an absolute scale by calibrating the signal strengths with those of F − from both SF 6 and CF 4 . These anion cross sections are normalized to vacuum-UV absorption cross sections, where available, and the resulting quantum yields are reported. Anion appearance energies are used to calculate upper limits to 298 K bond dissociation energies for D o ( CF 3 − X ) , which are consistent with literature values. We report new data for D o ( CF 2 I + - F ) ≤ 2.7 ± 0.2   eV and Δ f H 298 o ( CF 2 I + ) ≤ ( 598 ± 22 )   kJ mol − 1 . No ion-pair formation is observed below the ionization energy of the parent molecule for CF 3 Cl and CF 3 Br , and only weak signals (in both I − and F − ) are detected for CF 3 I . These observations suggest that neutral photodissociation is the dominant exit channel to Rydberg state photoexcitation at these lower energies.
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Identifikatoren
ISSN: 0021-9606
eISSN: 1089-7690
DOI: 10.1063/1.3137103
Titel-ID: cdi_scitation_primary_10_1063_1_3137103Vacuum_UV_negative_p
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