Cross sections

Cross section calculation

Nathan S. Jacobson (NASA Glenn)

Ionization cross sections are a critical parameter in determining the proportionality of measured ion intensity to vapor pressure, according to:

Here PA is the vapor pressure of a species A; k is the instrument constant; IA(E) is the ion intensity which is a function of the electron ionizing energy, E; T is the absolute temperature; and σA(E) is the ionization cross section which is also a function of electron ionizing energy, E.

Ionization cross sections have been measured and calculated via several methods. These methods are best described in the review by Drowart et al.1 This review also discusses scaling the ionization cross according to ionizing electron energy. The original program for this by Bonnell1 uses the Mann2 cross sections and scales them using the using the Bell coefficients3. It has been updated by J. Auping, NASA Glenn Research Center and is given on this website (see file download below; to download please click on the file pointing down on the right side).

1. J. Drowart, C. Chatillon, J. Hastie, and D. Bonnell, Pure Appl. Chem. 77 [4], 683-737 (2005).

2. J. B. Mann. In Recent Developments in Mass Spectroscopy, Proceedings of the International Conference on Mass Spectrometry, ed. by K. Ogata and T. Hayakawa, University Park Press, 814-819 (1969).

3. K. L. Bell, H. B. Gilbody, J. G. Hughes, A. E. Kingston, and F. J. Smith, J. Phys. Chem. Ref. Data 12, 891-916 (1983).