  Intervalley charged-impurity scattering processes are examined. It is found
that the scattering probability is enhanced due to the Coulomb interaction with
the impurity by the Sommerfield factor $F_Z\propto
\epsilon^{2\sqrt{1-4g^2}-2}$, where $\epsilon$ is the electron energy and $g$
is the dimensionless constant of the Coulomb interaction.
