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The Ionization Energy of CF3: When Does Entropy Matter in Gas-Phase Reactions?



Karl K. Irikura


A minor controversy has emerged recently over the value of the ionization energy of the trifluoromethyl radical, CF3. Apparently solid evidence supports both high values, IEa {nearly equal to} 9.05 eV, and low values, IEa {nearly equal to} 8.65 eV. Examining the assumptions made in the analysis of the various experimental results shows that the root of the discrepancy is the role of entropy in low-pressure, gas-phase ion chemistry. The proper treatment of entropy has itself been a more fundamental controversy for a long time. In the zero-pressure limit, conservation of energy (δE) of a molecular collision is the primary consideration, but at the high-pressure limit the free energy (δG) dictates the outcome of a reaction: what pressures qualify as
Journal of the American Chemical Society
No. 33


entropy, free energy, ion chemistry, ionization energy, photoionization


Irikura, K. (1999), The Ionization Energy of CF<sub>3</sub>: When Does Entropy Matter in Gas-Phase Reactions?, Journal of the American Chemical Society (Accessed March 1, 2024)
Created September 1, 1999, Updated February 17, 2017