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 less than or equal to 13.08+/-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 AP(0)(CF2OH+/CF3OH)less than or equal to 13.830+/-0.005 eV and AP(0)(CF3+/CF3OH)less than or equal to 13.996+/-0.005 eV. While the exact nature of the lowest-energy fragment (nominally CF2OH+) is not clear, the CF3+ fragment threshold leads unambiguously to Delta H(f 298)degrees(CF3OH)greater than or equal to 217.2+/-0.9 kcal/mol and D-298(CF3-OH)less than or equal to 115.2+/-0.3 kcal/mol. With previously derived Delta H(f 298)degrees(CF3O)=-151.8(-1.1)(+1.7) kcal/mol, this yields D-298(CF3O-H)=117.5(-1.4)(+1.9) kcal/mol, very close to, or only slightly weaker than the O-H bond energy in water: D-298(CF3O-H)-D-298(HO-H)=-1.8(-1.4)(+1.9) kcal/mol approximate to 0 kcal/mol. Similarly, with the recently redetermined value for Delta H degrees(CF2O), this implies a 298 K reaction enthalpy for the 1,2-elimination of HF from CF3OH of 2.8(-1.1)(+1.7) kcal/mol. CF3OF and CF3OCl have also been examined by photoionization ionization. CF3OF produces a very weak parent, with an apparent adiabatic IP(CF3OF)less than or equal to 12.710+/-0.007 eV. An analysis of the CF3+ and CF2O+ fragments from CF3OF, when combined with literature data, suggests Delta H(f 298)degrees(CF3OF)=-176.9+/-1.8 kcal/mol. The fitted value for the appearance potential of CF3+ from CF3OCl, AP(0)(CF3+/CF3OCl)less than or equal to 12.85+/-0.01 eV, leads to Delta H(f 298)degrees(CF3OCl)greater than or equal to-175.6+/-1.0 kcal/mol, D-298(CF3-OCl)less than or equal to 88.4+/-0.3 kcal/mol, and D-298(CF3O-Cl)less than or equal to 52.8(-1.5)(+2.0) kcal/mol. (C) 1997 American Institute of Physics.