  We solve the three-body bound state problem in three dimensions for mass
imbalanced systems of two identical bosons and a third particle in the
universal limit where the interactions are assumed to be of zero-range. The
system displays the Efimov effect and we use the momentum-space wave equation
to derive formulas for the scaling factor of the Efimov spectrum for any mass
ratio assuming either that two or three of the two-body subsystems have a bound
state at zero energy. We consider the single-particle momentum distribution
analytically and numerically and analyse the tail of the momentum distribution
to obtain the three-body contact parameter. Our finding demonstrate that the
functional form of the three-body contact term depends on the mass ratio and we
obtain an analytic expression for this behavior. To exemplify our results, we
consider mixtures of Lithium with either two Caesium or Rubium atoms which are
systems of current experimental interest.
