Particle interactions were directly determined from the lateral compression
of two-dimensional plasma dust crystals confined in a parabolic potential
well. Measured particle separations combined with an equation of state for
the crystal were used to derive values for the particle screening length an
d the charge on the particles. The shape of the parabolic potential well wa
s confirmed by observing trajectories of single particles falling within th
e well. No evidence of a lateral particle-particle binding was observed.