Relative cross-sections and kinetic energy release values in dissociative negative ion formation by successive single-electron transfer from alkali metal targets

Abstract

Positive ions formed from C 2H 2 were collided with Cs, K and Na targets in the kiloelectronvolt energy range. The dissociative negative ion formations of C − 2 and C 2H − ions from C 2H + 2 ions and C − 2 ions from C 2H + ions with an alkali metal target were determined to be double-collision processes using the target density dependence. By considering the reaction energies and comparing with reionization to positive ions, main processes of the dissociative negative ion formations were assigned to successive single-electron transfers with the dissociation of excited neutrals. The kinetic energy release values at FWHM of C 2H − ions from C 2H + 2 ions were 0.55eV for Cs, 0.28 eV for K and 0.17eV for Na. The relative cross-sections of C 2H − ions from C 2H + 2 ions to those of C 2H − ions from C 2H + 2 ions were 5.35 for Cs, 1.89 for K and 0.32 for Na. These dependences on target species are discussed in relation to the energy difference for the exothermic neutralization.