  Results. We consider the problem of isotropic collisions between an alkali
atom and neutral hydrogen. We calculate the collisional tensorial components of
general p and s-states, characterized by their effective principal quantum
number $n^{*}$. It is found that the behaviour of the tensorial components obey
simple power laws allowing quick calculations of the depolarizing collisional
rates. As application, our results should allow a rigorous treatment of the
atomic polarization profiles of the D1 -D2 lines of alkali atoms.
  Conclusions. Close coupling treatments of atomic collisions are needed to
decipher the information encoded in the polarized radiation from the Sun.
Important problems remain unresolved like the role of collisions in the
Paschen-Back conditions.
