  We explore the evolution of the mass distribution of dust in
collision-dominated debris disks, using the collisional code introduced in our
previous paper. We analyze the equilibrium distribution and its dependence on
model parameters by evolving over 100 models to 10 Gyr. With our numerical
models, we confirm that systems reach collisional equilibrium with a mass
distribution that is steeper than the traditional solution by Dohnanyi (1969).
Our model yields a quasi steady-state slope of n(m) ~ m^{-1.88} [n(a) ~
a^{-3.65}] as a robust solution for a wide range of possible model parameters.
We also show that a simple power-law function can be an appropriate
approximation for the mass distribution of particles in certain regimes. The
steeper solution has observable effects in the submillimeter and millimeter
wavelength regimes of the electromagnetic spectrum. We assemble data for nine
debris disks that have been observed at these wavelengths and, using a
simplified absorption efficiency model, show that the predicted slope of the
particle mass distribution generates SEDs that are in agreement with the
observed ones.
