  Spin-orbit scattering suppresses Zeeman splitting of individual energy levels
in small metal particles. This suppression becomes significant when the
spin-orbit scattering rate \tau_{so}^{-1} is comparable with the quantum level
spacing \delta. The g-factor exhibits mesoscopic fluctuations; at small
\delta\tau_{so} it is distributed according to the Maxwell distribution. At
\delta\tau_{so}\to 0 the average g-factor levels off at a small value
g\sim(l/L)^{1/2} given by the ratio of the electron mean free path l to the
particle size L. On the contrary, in 2D quantum dots the g-factor is strongly
enhanced by spin-orbit coupling.
