Electron-impact total ionization cross sections of CF{sub 4}, C{sub 2}F{sub 6}, and C{sub 3}F{sub 8}

Journal Article · Mon Feb 01 04:00:00 EST 1999 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.478270· OSTI ID:307258

Nishimura, H ^[1]; Huo, W M ^[2]; Ali, M A ^[3]; Kim, Y ^[4]

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1. Department of Physics, Niigata University, Niigata 950-21 (Japan)
2. NASA Ames Research Center, Moffet Field, California 94035-1000 (United States)
3. Department of Chemistry, Howard University, Washington, District of Columbia 20059 (United States)
4. National Institute of Standards and Technology, Gaithersburg, Maryland 20899-0001 (United States)

Both theoretical and experimental electron-impact total ionization cross sections of CF{sub 4}, C{sub 2}F{sub 6}, and C{sub 3}F{sub 8} are presented. The experimental cross sections have been measured as a function of incident electron energy {ital T} from threshold to 3 keV. A parallel plate condenser type apparatus was used. The molecular polarizability for C{sub 3}F{sub 8} was empirically estimated to be {alpha}=10.6&hthinsp;{Angstrom}{sup 3}{plus_minus}0.8&hthinsp;{Angstrom}{sup 3}. Theoretical cross sections calculated from the binary-encounter-Bethe (BEB) method, which combines a modified form of the Mott cross section and the Bethe cross section, are compared with the experimental cross sections. The BEB cross sections calculated from correlated molecular wave functions with theoretical estimates for multiple ionization are about 10{percent} higher than the experimental data at the peak for CF{sub 4}, while they are in excellent agreement with the experimental data for C{sub 2}F{sub 6} and C{sub 3}F{sub 8}. Our analysis shows that the BEB theory implicitly includes part of neutral dissociation, such as CF{sub 4}{r_arrow}CF{sub 3}+F, and hence tends to be an upper limit to the total ionization cross section. We found that the difference between our best theory for CF{sub 4} and the present experimental cross section exhibits a remarkable similarity to the shape of the recently measured cross section for neutral dissociation, though there is no {ital a priori} reason for the similarity. Owing to the large number of bound electrons, the correlation included in our wave functions for C{sub 2}F{sub 6} and C{sub 3}F{sub 8} is more limited than for CF{sub 4}. Hence, we believe that for these two molecules the calculated cross sections are lower than the true BEB values, in spite of the apparent excellent agreement between the theory and the experiment. {copyright} {ital 1999 American Institute of Physics.}

• OSTI ID: 307258
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 8 Vol. 110; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CARBON TETRAFLUORIDE
ELECTRON-MOLECULE COLLISIONS
ETCHING
FLUORINATED ALIPHATIC HYDROCARBONS
IONIZATION
ORGANIC COMPOUNDS
PLASMA
TOTAL CROSS SECTIONS