Spin depolarizing effect in collisions of simple/complex atoms in spherically symmetric states with neutral hydrogen

¹ Observatoire de Paris-Meudon, LERMA UMR CNRS 8112, 5 place Jules Janssen, 92195 Meudon Cedex, France e-mail: Moncef.Derouich@obspm.fr
² Department of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden

Received: 18 March 2005
Accepted: 9 May 2005

Abstract

We present a general semi-classical treatment of the depolarization of spherically symmetric states (i.e. s-states) which necessarily accounts for the exchange interaction via exchange perturbation theory. Calculations of the destruction rate of orientation of general s-states, characterized by their effective principal quantum number n^*, due to isotropic collisions with neutral hydrogen have been carried out. It is found that the behaviour of the depolarization rates with n^* obeys a power law. We express the depolarization and polarization transfer rates of complex atoms in terms of the depolarization rates of simple atoms. These results are used to infer the all non-zero depolarization and polarization transfer rates of the lower levels of the multiplets 42 and 145 of neutral . Further, we explain how our results can be used to easily calculate the hyperfine depolarization and polarization transfer rates. In order to validate our general theory, we have computed the destruction rate of orientation of the ground levels of the alkali metals , , , and using the quantum chemistry potentials of Geum et al.  (2001, J. Ch. Phys., 115, 5984), employing our semi-classical description of the collision dynamics. For ground state, the percentage error on our destruction rate of the orientation with respect to the fully quantal rate of Kerkeni et al. (2000b, A&A, 364, 937; note Erratum) is less than 1% at  K.