Dynamical maps of the domain between the 2/1 and 3/2 MMRs, for two fictitious systems composed of a solar-mass star and two planets with masses m₁ = m₂ = 1.0 M_J (top panel) and m₁ = m₂ = 0.1   M_J (bottom panel). The initial conditions are e₁ = 0 and σ₁ = 0; Δϖ is fixed at 0 (positive values on the e₂-axis) or 180° (negative values on the e₂-axis). The location of several MMRs are shown as vertical dashed lines. The light-gray tones correspond to regions of regular motion, while the hatched red regions correspond to strongly chaotic motion.