A study of relative level populations in beam-foil excited Li, Be, and Mg

Abstract

We have studied the optical beam-foil spectra of Li, Be, and Mg in the wavelength region 200-550nm by use of a quantum efficiency calibrated monochromator at projectile energies of 210keV for Li, 156, 256, and 356keV for Be, and 100keV for Mg. The relative population for different Rydberg levels of the same term series decreases in most cases somewhat faster than (n*) -a, as is also observed in ion-atom encounters under single collision conditions. The relative level population for levels of the same principal quantum number increases generally with the orbital angular momentum quantum number, and superimposed on this increase is a peaking for p levels. The relative population of levels of the same charge state and with the same core configuration is unaffected by change of the projectile energy.

A beam-foil study of lifetimes and level excitations in gallium and thallium

“…However, for Mg I, in which there are two electrons outside the closed K and L shells, there are for several levels disagreements between experimental and the NCA results [1] (we mention parenthetically that also more elaborate theoretical methods can fail [1]). Also, whereas in the light elements studied [4], the f and g levels are strongly populated, the 4f and the g terms in ZnII seem to be remarkably weakly populated [5,6]. On the other hand, there are in some of the neutral level shemes of group three elements fairly low-lying displaced terms e.g.…”

“…The experimental set up [1,9] as well as the quantum efficiency calibration of the monochromator [4,10,11] have been described previously. Line intensities taken from the spectrograms were converted into relative level populations as described in [4,11] and by using the NCA transition probabili-ties. Line intensities taken from the spectrograms were converted into relative level populations as described in [4,11] and by using the NCA transition probabili-ties.…”

“…As pointed out in [1], that is what is needed when evaluating excitation cross sections or excitation probabilities in experimental studies of electronic or atomic collisions and beam-foil excitations. Until now, only excitation of light elements has been studied, see [4] and references given there. However, for Mg I, in which there are two electrons outside the closed K and L shells, there are for several levels disagreements between experimental and the NCA results [1] (we mention parenthetically that also more elaborate theoretical methods can fail [1]).…”

“…More elaborate methods are unable to provide the needed complete sets of transition probabilities. Consequently, a study of the excitation mechanism using Ga and T1 projectiles is of basic interest, especially because some of the excited levels of these elements have large quantum defects, contrary to the light elements studied hitherto [4]. Although the NCA method thus may disagree with experimental data for the case of two electrons outside closed shells, it is worth to see, whether group three atoms, which have three electrons outside closed shells, can be treated sufficiently well by the NCA method, because the normal terms of such atoms are of configuration s2(1So)nl (n and l being the principal quantum number and the orbital angular momentum quantum number of the excited term, respectively), so that the excited electron moves in a spherically symmetric field.…”

“…Although the NCA method thus may disagree with experimental data for the case of two electrons outside closed shells, it is worth to see, whether group three atoms, which have three electrons outside closed shells, can be treated sufficiently well by the NCA method, because the normal terms of such atoms are of configuration s2(1So)nl (n and l being the principal quantum number and the orbital angular momentum quantum number of the excited term, respectively), so that the excited electron moves in a spherically symmetric field. It is thus of interest to see, whether the systematics observed for light elements [4] also hold generally for heavy species, making the Zn II data [5,6] exceptions from the general trends [4], or whether the Zn II data indicate general changes in level populations as the projectile atomic number increases. of configuration p2nl which have configuration mixings with some of the normal terms.…”