Carbon K-shell x-ray and Auger-electron production in hydrocarbons and carbon oxides by 0.6–2.0-MeV protons

Carbon K-shell x-ray and Auger-electron-production cross sections are reported for 0.6–2.0-MeV protons incident on ${\mathrm{CH}}_4$ (methane), ${\mathrm{C}}_2$${\mathrm{H}}_2$ (acetylene), n-${\mathrm{C}}_4$${\mathrm{H}}_{10}$ (normal butane), i-${\mathrm{C}}_4$${\mathrm{H}}_{10}$ (isobutane), ${\mathrm{C}}_6$${\mathrm{H}}_6$ (benzene), CO, and ${\mathrm{CO}}_2$. A variable-geometry end-window proportional counter with an alternate procedure for the determination of its transmission was used in collection of the x-ray data. A constant-energy-mode π/4 parallel-plate electrostatic analyzer served in the detection of Auger electrons. K-shell Auger-electron-production cross sections are compared with the predictions of the first Born theory and the perturbed-stationary-state theory which accounts for energy-loss, Coulomb deflection, and relativistic effects (ECPSSR). These data show fair agreement with the ECPSSR theory when the chemical shifts, of the carbon K-shell binding energy in molecules, are included in the calculations. This agreement is even better after effects of intramolecular scattering are considered. Validity of the geometrical model by Matthews and Hopkins [Phys. Rev. Lett. 40, 1326 (1978)] is established after a scrutiny of the inelastic cross sections for scattering of Auger-electrons within the molecule and their effective dislocation out of the detector’s window. The x-ray cross sections show particularly strong variations with the target molecular species because of additional changes due to modifications in the fluorescence yields for molecular carbon. The correlation of these changes with the molecular character of carbon and a scaling procedure for the fluorescence yields in molecules will be discussed elsewhere.