Prompt and time-delayed electron decay-in-flight spectra of gas-excited carbon ions

Auger-electron emission from 400keV carbon ions excited in single gas collisions with CH₄, Ne, and Ar has been investigated. Prompt and time-delayed projectile electron-emission spectra have been measured, and spectroscopic assignments are given. Absolute inner-shell vacancy-production cross sections and relative line intensities deduced from the prompt and time-delayed spectra for excited carbon ions have been compared as a function of exciter gases. An enhanced probability for electron excitation into high-spin states in carbon is found. Especially for the collision system C⁺{→}Ne, a striking population of the 1s2s2p⁴Pᵒ quartet state relative to the berylliumlike quintet and boronlike sextet states is observed. It is assumed that this is accounted for by cascade-feeding mechanisms. In particular, cascades from Rydberg levels feeding the CIV 1s2s2p⁴Pᵒ, CIII 1s2s2p²⁵P, and CII 1s2s2p³⁶Sᵒ high-spin states are discussed. Finally, wavelengths associated with electric dipole ($E1$) transitions among quintet terms in C III and sextet terms in C II are predicted using ab initio methods.