Ionization Cross Sections, Charge-Transfer Cross Sections, and Ionic Fragmentation Patterns of Some Paraffins, Olefins, Acetylenes, Chloroalkanes, and Benzene with 40–100-keV Protons

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Abstract
The simple and charge‐transfer ionization cross sections for Kr, Ne, N2, CH4, C2H4, and n‐C4H10 were measured with 40–100‐keV protons. The simple ionization cross sections are almost constant in this range, while the charge‐transfer cross sections are roughly 40% of the total ionization at 40 keV and decrease to about 10% at 100 keV. The relative ionization cross sections (both simple and charge transfer) of a variety of molecular compounds (see title) were measured with 100‐keV protons and found to be linearly related to the polarizabilities. The mass spectra of a number of hydrocarbons were measured with 50‐ and 100‐keV protons. The mass spectra are qualitatively very similar to spectra obtained with electrons of the same velocity (55 eV for 100‐keV protons). This is to be expected from a qualitative extension of the Bethe—Born equation to ionization of molecular electrons. Since the mass spectra change little with velocity the American Petroleum Institute (A.P.I.) fragmentation patterns with 50–75‐V electrons are a good guide to ionization by any (singly) charged particle with velocity higher than 108 cm/sec. Fragments of high appearance potentials and doubly charged ions are considerably more abundant in the 40–100‐keV proton spectra than at higher proton energies or in the electron‐impact spectra. Conclusions can be made as to the charge‐exchange mass spectra produced by particles with velocities in the range 108 cm/sec. These mass spectra are very different from charge‐transfer spectra obtained at low primary ion energies. Thus there is little dependence on the recombination energy of the primary ion. The charge‐transfer spectra seem not very different from the spectra produced by simple ionization. This means that the distribution of internal energies imparted to the new ion cannot be very different from that in pure ionization.