Showing papers by "Eric G. Cavalcanti published in 2003"

CH4 ionization and dissociation by proton and electron impact

Abstract: Absolute dissociative and non-dissociative ionization cross sections of CHn+ (n = 0–4) molecules by protons in the 0.5–3.5 MeV impact energy range have been measured. The present results are in good agreement with the previously published data, where overlap occurs. A decay-route model for CH4 dissociation induced by proton impact is proposed and a method to obtain the corresponding branching ratios is introduced. The consistency and extent of the proposed model and methodology is verified through its application in the case of electron-impact dissociation.

Absolute cross sections for multiple ionization of noble gases by swift proton impact

Abstract: Absolute cross sections, σq+, for multiple ionization of He (q = 1), Ne (q = 1, 2, and 3), Ar (q = 1, 2, 3, and 4), Kr (q = 1, 2, 3, and 4), and Xe (q = 1, 2, 3, 4, and 5) atoms by protons in the 075–35 MeV impact energy range have been measured The present results are in good agreement with the previously published data in the case of the single-and double-ionization cross sections, but some non-systematic discrepancies appear for higher charge states A detailed comparison with electron impact cross sections in these gases is performed, and it shows that the cross sections for single ionization by high-velocity protons are substantially smaller than those corresponding to equi-velocity electrons for heavier targets

Postcollisional decay in Ne multiple ionization by H2+ ions in breakup collisions

Abstract: We measured the ${\mathrm{Ne}}^{q+}$ charge-state yield distribution for Ne atoms multiply ionized by 1-MeV/amu ${\mathrm{H}}_{2}^{+},$ in coincidence with the final state of the projectile, for both breakup and nonbreakup channels. Measurements with 1-MeV ${\mathrm{H}}^{+}$ projectiles were also performed. While the ${\mathrm{H}}_{2}^{+}$ nonbreakup channel produces results similar to equal-velocity proton or electron projectiles, the breakup channels lead to a charge-state yield distribution very close to the known Ne ${2s}^{\ensuremath{-}1}$ postcollisional decay distribution, measured through photoionization [T. A. Carlson, W. E. Hunt, and M. O. Krause, Phys. Rev. 151, 41 (1966)]. This behavior suggests that, in the breakup channels, contributions to multiple ionization from mechanisms that are usually considered to be dominant in ion-atom collisions are less important than the postcollisional decay.