1. Ladd, M. F. C., and Lee, W. H., Acta Cryst., 13, 959 (1960).
2. Massey, H. S. W., Negative Ions, second ed., 22 (Cambridge University Press, London, 1950).
3. Sommer, H., Thomas, H. A., and Hipple, J. A., Phys. Rev., 82, 697 (1951).
4. Berry, C. E., J. App. Phys., 25, 28 (1954).
5. Hebling, A., and Lichtman, D., “Fragment Patterns and Appearance Potentials Using the Omegatron Mass Spectrometer”, Ninth Ann. Meet. Amer. Soc. Test. Materials Comm. E-14 on Mass Spectrometry, Chicago, Ill. (June 4–9, 1961).