Sixty years of spectroscopic research: a tribute to Professor Edward B. M. Steers

Charge transfer from doubly charged ions of transition elements in a neon glow discharge: evidence based on emission spectra

“…Here, ΔE = E i − E k and g i , g k are the respective statistical weights (degeneracy factors) of the levels involved. Equation (11) says that EI deexcitation cross sections (i → k, σ ik ) and the corresponding EI excitation cross sections (k → i, σ ki ) are comparable, whilst a provision is made for the fact that, in case of excitation, the corresponding energy must be higher by the excitation threshold, ΔE = E i − E k . Excitation cross sections were published for Cu + and Fe + ions [33,41], their values are in the order of 10 −18 to 10 −15 cm 2 and 10 −18 to 10 −17 cm 2 , respectively.…”

“…Another sign that radiatively-dominated deexcitation is a good approximation for a Grimm-type GD is that in cascade excitation/deexcitation processes like that shown in figure 3, there are no levels for which a negative TR balance would arise, i.e. the situation in which the observed radiative population rate would significantly 11 exceed the observed radiative depopulation rate. If an intermediate level of such a cascade is not subject to additional collisional excitation, prospective significant EI depopulation would demonstrate itself by a negative radiative TR balance of that level.…”

“…The first fact to realize is that, in optical spectroscopy, we can see only emission from non-metastable excited atoms or ions. Therefore the character of the emission spectrum depends (1) on the electron structure of the atom or ion under study, i.e., the availability and energy distribution of the levels from 11 Beyond the measurement uncertainty.…”

“…This was a major step towards understanding how analytical glow discharges work. In numerous further studies listed in [11], Steers and his colleagues measured GD emission spectra of many elements at different conditions, e.g., with different discharge gases, and plotted intensity ratios of the emission lines observed as functions of their excitation energy. Thereby they were able to identify some selective reactions, such as CT, in which relative excitation cross sections for individual states accessible to these reactions peak in the close vicinity of a certain resonant energy.…”