The Journal of Physical Chemistry, Vol. 93, No. 18, 1989 6881
Comments of the decomposition of anisole, phenyl allyl ether, and phenyl ethyl ether are all therefore in good agreement regarding the heat of formation of the phenoxy radical, even though the studies were performed by different techniques and in different temperature ranges. These values are also in agreement with estimates of approximately 9 kcal mol-' from a wide variety of measurements, discussed in more detail in ref 2, and confirm the considerable resonance stabilization of this radical. Acknowledgment. The author thanks Dr. R. A. Back for helpful discussions. Registry No. C6H50CH3,100-66-3; C6H50,2122-46-5.
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Mass Spectrometrlc Studies of CF,' Sir: I was intrigued to read the paper by Hagenow, Denzer, Brutschy, and Baumgartel on the formation of CF4+ from CF4 clusters.' The decomposition of CF4 is indeed important and interesting work. Due to the nature of their experimental setup, it is difficult to compare much of their data directly to other studies of the pressure dependence of the relative yields of the CF4+ and CF3+ ions. Direct comparison with our data is limited by our ability to compare their vacuums and molecular beam arrangement with our own. Nonetheless, since the CF4+ion has been previously observed and measured? it is interesting to compare the data where possible. In particular, sufficient data are presented to compare the results on the ratio of the CF4+yield to CF3+yield as a function of electron impact energy. The electron energy dependence of this ratio Hagenow et al. report at a stagnation pressure of 2.5 bar is quite similar to data reported previously2 for a niass spectrometer pressure of 3 X lo-' Torr (see Figure 1). It is encouraging to see that the results obtained by Hagenow, Denzer, Brutschy, and Baumgartel are consistent with our results. Their reported ionization potential (of 15.77 eV) may be smaller than (1) Hagenow, G.; Denzer, W.; Brutschy, B.; Baumgartel, H. J . Phys. Chem. 1988, 92, 6487.
Figure 1. The ratio of the CF3'/CF4+ ion intensities as a function of electron impact energy. The pressures of 3 X lo-' Torr (-), 3 X 10-6 Torr ( 0 ) ,and 4.5 X lod Torr (+) from ref 1 are uncorrected for ion gauge cross section. Data for a stagnation pressure po = 3.5 bar ( X ) is from ref 2.
ours (16.2 eV) either because of commonly observed differences between photon and electron impact ionization mass spectroscopy or because of signal contributions from processes associated with clusters (CF&' and ion-molecule collisions.* Earlier authors3 have inferred the existence of the CF4+ ion by extrapolating to zero pressure the (linear) relationship between the dissociation ion product (CF,+) and the background gas pressure. (2) Kime, Y. J.; Driscoll, D. C.: Dowben. P. A. J . Chem. Soc.. Faradav Trans. 2 1987,83,403. ( 3 ) Deutsch, H.; Leiter, K.; Mark, T. D. Inf. J. Mass Specfrom. Ion Processes 1985, 67, 191.
Department of Physics Syracuse University Syracuse, New York 13244- 1 1 30
Yolanda J. Kime* Peter A. Dowben
Received: March 17, 1989; In Final Form: June 14, 1989
