Quenching of Ar +( 2P[formula omitted]) at high pressures in an electron-impact ion source

Abstract

Investigations of the non-reactive scattering of Ar + by N 2 using a crossed-beam apparatus reveal that the two spin-orbit states of Ar + are back-scattered into different regions of velocity space (center-of-mass reference frame); this fact permits the ratio of these two states in the primary ion beam to be monitored as a function of ion source conditions. Adjustments of source pressure and ionizing current density are the key parameters which control the extent of quenching of the Ar + ( 2 P 1 2 ) initially formed by electron impact on Ar. Superelastic scattering of electrons is suggested as a probable mechanism and a rate coefficient, k ≥ 8 × 10 −11 cm 3 s −1, is estimated for the reaction Ar + 2 P 1 2 ) + e − → Ar +( 2 P 3 2 ) + e − + 0.18 eV