On the heat of formation of carbonyl fluoride, CF{sub 2}O
- Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439-4831 (United States)
In light of the recent controversy surrounding its heat of formation, CF{sub 2}O was reexamined by photoionization mass spectrometry. In particular, the CO{sup +} fragment ion yield curve from CF{sub 2}O was interpreted in terms of a retarded CO{sup +}+F{sub 2} process, and a more facile two-step fragmentation to CO{sup +}+2F. The former process produces a weak, slowly growing tail region without a clear onset, while the latter occurs at higher energy and causes a pronounced growth with a conspicuous onset, which was found to occur at {le}20.87{sup +0.03}/{sub {minus}0.07} eV at 0 K by fitting with a model curve that incorporates {open_quote}{open_quote}fluctuations{close_quote}{close_quote} associated with second-generation fragments. This onset leads to {Delta}{ital H}{sub {ital f}}{sup {degree}}{sub 298}(CF{sub 2}O) {ge}{minus}149.1{sup +1.4}/{sub {minus}0.7} kcal/mol, and indicates that the older experimental values for this quantity are too low by at least 3{endash}4 kcal/mol. While the F{sub 2} elimination is retarded by competition with lower energy processes, the two-step process derives its strength from the FCO{sup +} fragment, which assumes the role of a pseudoparent. Thus, the onset of CO{sup +}+2F is expected to appear reasonably close to the thermochemical threshold. Such an interpretation indicates that recently calculated {ital ab} {ital initio} values of {minus}145.3{plus_minus}1.7 kcal/mol and {minus}145.6{plus_minus}1.0 kcal/mol are very likely too high by 3{endash}4 kcal/mol. In addition, the adiabatic ionization potential of CF{sub 2}O was refined to 13.024{plus_minus}0.004 eV, while the 0 K appearance potential of the FCO{sup +} fragment was found by fitting to be {le}14.752{plus_minus}0.005 eV. (Abstract Truncated)
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 397443
- Journal Information:
- Journal of Chemical Physics, Vol. 105, Issue 22; Other Information: PBD: Dec 1996
- Country of Publication:
- United States
- Language:
- English
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