Semi-classical theory of collisional depolarization of spectral lines by atomic hydrogen I. Application to p states of neutral atoms

The present paper extends the method of Anstee, Barklem and O'Mara (Anstee 1992; Anstee & O'Mara 1991, 1995; Anstee et al. 1997; Barklem 1998; Barklem & O'Mara 1997; Barklem et al. 1998), developed during the 1990s for collisional line broadening by atomic hydrogen, to the depolarization of spectral lines of neutral atoms by collisions with atomic hydrogen. In the present paper, we will limit the calculations to p(l = 1) atomic levels. The depolarization cross sections and depolarization rates are computed. In Table 2 cross sections as functions of the relative velocity and effective quantum number are given, allowing for the computation for any p atomic level. Our results are compared to quantum chemistry calculations where possible. The sensitivity of depolarization cross sections to regions of the potential is examined. We conclude that the accuracy obtained with our method (<20% for the depolarization rates) is promising for its extension to higher l-values for the interpretation of the "second solar spectrum". This will be the object of further papers.