On the heats of formation of trifluoromethyl radical CF{sub 3} and its cation CF{sub 3}{sup +}
- Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439-4831 (United States)
The CF{sup +} and CF{sub 3}{sup +} fragment ion yield curves from C{sub 2}F{sub 4} have been remeasured by photoionization mass spectrometry. Fits with appropriate model curves yield the appearance potentials AP{sub 0}(CF{sub 3}{sup +}C{sub 2}F{sub 4})=13.721{plus_minus}0.005 eV and AP{sub 0}(CF{sup +}/C{sub 2}F{sub 4})=13.777{plus_minus}0.005 eV and an accurate difference in ionization potentials, IP(CF){minus}IP(CF{sub 3})=0.055{plus_minus}0.003 eV. With the existing photoelectron value IP(CF)=9.11{plus_minus}0.01 eV, this produces IP(CF{sub 3})=9.05{sub 5}{plus_minus}0.01{sub 1} eV. The CF{sub 3}{sup +} fragments from CF{sub 3}Cl, CF{sub 3}Br, and CF{sub 3}I have also been remeasured, and their ion yield curves fitted with model functions. The experimentally derived AP{sub 0}(CF{sub 3}{sup +}/CF{sub 3}Cl){lt}12.867{plus_minus}0.008 eV has been found to be only an upper limit. The Analogous CF{sub 3}{sup 3}CF{sub 3}{sup +} fragment yield curves from CF{sub 3}Br and CF{sub 3}I produce AP{sub 0}(CF{sub 3}{sup +}/CF{sub 3}Br)=12.095{plus_minus}0.005 eV and AP{sub 0}(CF{sub 3}{sup +}/CF{sub 3}I)=11.384{plus_minus}0.005 eV, leading to D{sub 0}(CF{sub 3}{minus}Br)=70.1{plus_minus}0.3 kcal/mol (70.8{plus_minus}0.3 kcal/mol at 298 K) and D{sub 0}(CF{sub 3}{minus}I)=53.7{plus_minus}0.3 kcal/mol (54.3{plus_minus}0.3 kcal/mol at 298 K). Based on tabulated values for {Delta}H{sub f}{sup {circ}}(CF{sub 3}Br) and {Delta}H{sub f}{sup {circ}}(CF{sub 3}I), which appear to be inconsistent by {approximately}1 kcal/mol, a compromise value of {Delta}H{sub 298}{sup f{circ}}(CF{sub 3})={minus}111.4{plus_minus}0.9 kcal/mol ({minus}110.7{plus_minus}0.9 kcal/mol at 0 K) is selected, resulting in {Delta}H {sub 298}{sup f{circ}}(CF{sub 3}{sup +})=97.4{plus_minus}0.9 kcal/mol (98.1{plus_minus}0.9 kcal/mol at 0 K). Additionally, IP(CF{sub 4}){equivalent_to}AP{sub 0}(CF{sub 3}{sup +}/CF{sub 4})=14.67{plus_minus}0.04 eV can be inferred. (Abstract Truncated)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 435119
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 1 Vol. 106; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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