A photoionization study of trifluoromethanol, CF3OH, trifluoromethyl hypofluorite, CF3OF, and trifluoromethyl hypochlorite, CF3OCl

CF3OH, an important and controversial by-product of atmospheric decomposition of CF3CFH2 ~HFC-134a! and other hydrofluorocarbons, has been examined by photoionization mass spectrometry. The ionization onset is characterized by a broad Franck–Condon distribution, arising primarily from a substantial elongation of the C–O bond upon ionization. An upper limit to the adiabatic ionization potential ~IP! of < 13.08 6 0.05 eV has been established. The appearance potentials ~APs! of the first two fragments have been accurately determined by fitting with appropriate model functions as AP0~CF2OH /CF3OH!<13.83060.005 eV and AP0~CF3 /CF3OH!<13.99660.005 eV. While the exact nature of the lowest-energy fragment ~nominally CF2OH ! is not clear, the CF3 1 fragment threshold leads unambiguously to DHf 298 + ~CF3OH!>2217.260.9 kcal/mol and D298~CF3–OH!<115.260.3 kcal/mol. With previously derived DHf 298 + ~CF3O!52151.821.1 11.7 kcal/mol, this yields D298~CF3O–H! 5117.521.4 11.9 kcal/mol, very close to, or only slightly weaker than the O–H bond energy in water: D298~CF3O–H!–D298~HO–H!521.821.4 11.9 kcal/mol'0 kcal/mol. Similarly, with the recently redetermined value for DHf + ~CF2O!, this implies a 298 K reaction enthalpy for the 1,2-elimination of HF from CF3OH of 2.821.1 11.7 kcal/mol. CF3OF and CF3OCl have also been examined by photoionization. CF3OF produces a very weak parent, with an apparent adiabatic IP~CF3OF! <12.71060.007 eV. An analysis of the CF3 1 and CF2O 1 fragments from CF3OF, when combined with literature data, suggests DHf 298 + ~CF3OF!52176.921.3 11.8 kcal/mol. The fitted value for the appearance potential of CF3 1 from CF3OCl, AP0~CF3 /CF3OCl!<12.8560.01 eV, leads to DHf 298 + ~CF3OCl!>2175.661.0 kcal/mol, D298~CF3–OCl!<88.460.3 kcal/mol, and D298~CF3O– Cl!<52.821.5 12.0 kcal/mol. © 1997 American Institute of Physics. @S0021-9606~97!03122-X#