## Detalles de publicación

PP 06054

## Spin depolarizing effect in collisions with neutral hydrogen \\ II. Application to simple/complex ions in spherically symmetric states

(1)Instituto de Astrof\'isica de Canarias, E-38205 La Laguna,
Tenerife, Spain
(2)Department of Astronomy and Space Physics, Uppsala University, Box 515, S 751 20 Uppsala, Sweden

Aims. To develop an accurate and general semi-classical formalism which deals with the definition and the calculation of the collisional depolarizing constants of the levels of simple and complex singly ionized atoms in arbitrary $s$-states perturbed by collisions with hydrogen atoms. The case of ions with hyperfine structure is fully investigated.

Methods. Potential energy curves based on the MSMA exchange perturbation theory employing the Unsold approximation are obtained. These potentials enter the Schrodinger equation to determine the collisional $T$-matrix elements in a semi-classical description. The $T$-matrix elements are used for the calculation of the collisional depolarization rates of simple atoms. These rates are then used to calculate the rates in cases of complex and/or ions with hyperfine structure.

Results. We have estimated the collisional depolarization and polarization transfer rates of the ground levels of the ionized alkaline earth metals \ion{Be}{ii}, \ion{Mg}{ii}, \ion{Ca}{ii}, \ion{Sr}{ii}, and \ion{Ba}{ii}. We have studied the variation of the collisional rates with effective principal quantum number $n^*$ characterizing an arbitrary $s$-state of a perturbed simple ion. We find that the collisional rates for simple ions obey simple power laws as a function of $n^*$. We present direct and indirect formulations of the problem of the calculation of the depolarization and polarization transfer rates of levels of complex atoms and hyperfine levels from those for simple atoms. In particular, the indirect method allows a quick and simple calculation employing the simple power-law relations. For the state $4s$ $^2S_{1/2}$ of \ion{Ca}{ii}, our computed rate of the destruction of orientation differs from existing quantum chemistry calculations by only 4 \% at $T=5000$K.

Methods. Potential energy curves based on the MSMA exchange perturbation theory employing the Unsold approximation are obtained. These potentials enter the Schrodinger equation to determine the collisional $T$-matrix elements in a semi-classical description. The $T$-matrix elements are used for the calculation of the collisional depolarization rates of simple atoms. These rates are then used to calculate the rates in cases of complex and/or ions with hyperfine structure.

Results. We have estimated the collisional depolarization and polarization transfer rates of the ground levels of the ionized alkaline earth metals \ion{Be}{ii}, \ion{Mg}{ii}, \ion{Ca}{ii}, \ion{Sr}{ii}, and \ion{Ba}{ii}. We have studied the variation of the collisional rates with effective principal quantum number $n^*$ characterizing an arbitrary $s$-state of a perturbed simple ion. We find that the collisional rates for simple ions obey simple power laws as a function of $n^*$. We present direct and indirect formulations of the problem of the calculation of the depolarization and polarization transfer rates of levels of complex atoms and hyperfine levels from those for simple atoms. In particular, the indirect method allows a quick and simple calculation employing the simple power-law relations. For the state $4s$ $^2S_{1/2}$ of \ion{Ca}{ii}, our computed rate of the destruction of orientation differs from existing quantum chemistry calculations by only 4 \% at $T=5000$K.