  To study the stability of heavy quarkonia in quark-gluon plasma, we use a
color-singlet Q-Qbar potential determined previously to be a well-defined
linear combination of the free energy F_1 and the internal energy U_1. Using
the lattice gauge results of Kaczmarek et al., the dissociation temperatures of
J/psi and chi_b in quenched QCD are found to be 1.62Tc and 1.18Tc respectively,
in good agreement with spectral function analyses. The dissociation temperature
of J/psi in full QCD with 2 flavors is 1.42Tc. Thus, the presence of dynamical
quarks in full QCD lowers the dissociation temperature of J/psi, but J/psi
remains bound up to 1.42Tc.
