Rl. Asher et al., A PHOTOIONIZATION STUDY OF TRIFLUOROMETHANOL, CF3OH, TRIFLUOROMETHYL HYPOFLUORITE, CF3OF, AND TRIFLUOROMETHYL HYPOCHLORITE, CF3OCL, The Journal of chemical physics, 106(22), 1997, pp. 9111-9121
CF3OH, an important and controversial by-product of atmospheric decomp
osition of CF3CFH2 (HFC-134a) and other hydrofluorocarbons, has been e
xamined 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 upp
er limit to the adiabatic ionization potential (IP) of less than or eq
ual to 13.08+/-0.05 eV has been established. The appearance potentials
(APs) of the first two fragments have been accurately determined by f
itting with appropriate model functions as AP(0)(CF2OH+/CF3OH)less tha
n or equal to 13.830+/-0.005 eV and AP(0)(CF3+/CF3OH)less than or equa
l to 13.996+/-0.005 eV. While the exact nature of the lowest-energy fr
agment (nominally CF2OH+) is not clear, the CF3+ fragment threshold le
ads 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)=-1
51.8(-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 en
ergy in water: D-298(CF3O-H)-D-298(HO-H)=-1.8(-1.4)(+1.9) kcal/mol app
roximate to 0 kcal/mol. Similarly, with the recently redetermined valu
e for Delta H degrees(CF2O), this implies a 298 K reaction enthalpy fo
r the 1,2-elimination of HF from CF3OH of 2.8(-1.1)(+1.7) kcal/mol. CF
3OF 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, sugges
ts Delta H(f 298)degrees(CF3OF)=-176.9+/-1.8 kcal/mol. The fitted valu
e 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)le
ss than or equal to 88.4+/-0.3 kcal/mol, and D-298(CF3O-Cl)less than o
r equal to 52.8(-1.5)(+2.0) kcal/mol. (C) 1997 American Institute of P
hysics.