New measurements of the cross sections of doubly excited resonances in calcium

Abstract

We report new cross section measurements, believed to be the first involving synchrotron radition together with a 'hot-wire' diode detector, in which we have observed the doubly excited series of C a I at a much improved signal to noise ratio using the radiation from the DORIS I I electron accelerator and the H 4 S Y L 4 B facilities. The data provide " e n information on the 'vanishing width' effect in Ca I and are compared with several calculations of the cross section reported in recent literature. The best representation of the detailed structure appears to be achieved by the most recent combination of MQDT with the R-matrix method. All the calculations ( R matrix and MBPT) underestimate the cross section in the 3d5p peak by 20-40%.

Photoionization of confined Ca in a spherical potential well

“…4, where they are seem to be in excellent agreement with the available experimental results [11]. This gives confidence that, using exactly the same theoretical methodology, our calculations should also be reliable for U 0 > 0.…”

“…The photoionization of the outer shell of neutral calcium has been studied using different methods in the past [6][7][8], and experimental data exist [9][10][11]. Three-state R-matrix calculations were found to be quite successful in describing the complex resonance structure endemic in outer-shell photoionization of free Ca [6]; thus, the R-matrix method was selected to perform the calculations.…”

Spin-orbit effects in the heavy alkaline-earth atoms

“…For such large basis sets the solution of the linear eigensystem (5) at many energies can become time consuming, and for this reason a much more efficient "streamlined" solution method of Greene (12) and 0 0 (13) This partitioning breaks Eq. (5) into two coupled matrix equations, I ccZc+ PCOZ0 (14) r"Z'+ r-Z'=be-Z' (15) Using (14) to eliminate Z' from (15) leads to a matrix equation of much smaller dimension for Z', specifically [I oo I oc(l cc) -Il co]Zo gAooZo (16) …”

“…Accounting for detailed spectroscopy of these heavy atoms, much of it only recently acquired [16],is a second major goal of this paper. Theoretical results are shown to adequately describe photoionization spectra of groundstate strontium and also of the ground state and an excited state of barium.…”

Two-photon double ionization of helium

“…By employing intermediate resonances, such as the 4s4p 1 P o state, experimentalists control the Ca · ion isotopes that are trapped [22,23,18]. We have recently demonstrated that the use of model potentials gives photoionization cross sections [20] in very good agreement with experiment [24] and the best other theoretical calculations [25]. In figure 3, we build on this work by presenting photoionization cross sections for the m 0 level of the 4s4p 1 P o state, which is used as an intermediate state in the trap loading experiments.…”