Electron-impact-excitation cross sections of lithiumlike ions

Abstract

We present an easy to use expression for cross sections of electron-impact-induced 1s 2 nl→1s 2 nЈlЈ excitation transitions with 2рnрnЈр4 in multiply charged ions of lithium isoelectronic sequence. This expression is based on our computations by convergent close-coupling ͑CCC͒ and Coulomb-Born with exchange and normalization ͑CBE͒ methods. We show scaling of the CCC and CBE cross sections with atomic number Z and use this scaling for presentation of the cross-section data. For 6рZр30 the scaling is accurate to better than Ϯ20% at any energy except in the vicinity of resonances. Contributions from indirect excitation channels do not scale with Z; however, for calculation of excitation rates it is enough to average locally these contributions over energy and to take them into account in a frame of a general scaling-based expression for the cross sections. For excitation rates, total inaccuracy caused by all simplifications in the cross-section presentation is likely to be less than Ϯ30% even for most risky cases. This assessment is based on comparison of excitation rates, computed using our scaling-based expression for the cross sections, with the excitation rates, computed using high-resolution ͑CCC and R matrix͒ cross sections and experimental data. ͓S1050-2947͑97͒06211-2͔

Feasibility of achieving gain in transition to the ground state of C VI at 34 nm

“…␤ 21 is given by (Obtained similarly by from the detailed balance relation applied to the impact-excitation cross section given in Ref. 26…”

Electron-impact broadening of the 3s–3p lines in low-Z Li-like ions

“…Such comparisons were done, e.g., for the R-matrix with pseudostates and K-matrix method results [15,16,17]. For higher-Z ions (Z ≥ 4), a detailed comparison of all excitation cross sections between the states with the principal quantum number n ≤ 4 has shown that the CCC data practically coincide with the perturbative Coulomb-Born-exchange calculations [18]. Furthermore, a recent paper on electron-impact excitation in Be II and B III (also including the transitions between the excited states up to n ≤ 4) again demonstrated a high level of agreement between the CCC and the K-matrix cross sections [17].…”

Accelerated recombination due to resonant deexcitation of metastable states

“…Our main source of excitation data is the Coulomb-Born-exchange unitarized code ATOM [15] which combines a high calculational speed with a good accuracy, especially for moderately-and highly-ionized atoms. Previously we have shown that ATOM excitation data for H-and Li-like ions very well agree with the cross sections calculated by the more sophisticated convergent close-coupling (CCC) method [17,18]. Nevertheless, a use of more precise data is made whenever possible; for example, our database of collisional cross sections for neutral Helium was developed using the latest recommended CCC fits [19].…”