  We present new results for the phase space factors involved in double beta
decay for beta-beta- transitions to ground states and excited 0+1 states, for
isotopes of experimental interest. The Coulomb distortion of the electron wave
functions is treated by solving numerically the Dirac equation with inclusion
of the finite nuclear size and electron screening effects, and using a Coulomb
potential derived from a realistic proton density distribution in the daughter
nucleus. Our results are compared with other results from literature, obtained
in different approximations, and possible causes that can give differences are
discussed.
