Electron-impact ionization of the metastable excited states of Li+

Electron-impact ionization cross sections for the 1s2s1S and 1s2s3S metastable states of Li+ are calculated using both perturbative distorted-wave and non-perturbative R-matrix with pseudo-states and time-dependent close-coupling methods. Term-resolved distorted-wave calculations are found to be approximately 15% above term-resolved R-matrix with pseudostates calculations. On the other hand, configuration-average time-dependent close-coupling calculations are found to be in excellent agreement with the configuration-average R-matrix with pseudostates calculations. The non-perturbative R-matrix and close-coupling calculations provide a benchmark for experimental studies of electron-impact ionization of metastable states along the He isoelectronic sequence