  We study the nucleon-nucleon (NN) problem as a six-quark system in a
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between the quarks. This interaction has a long range Yukawa-type
part, depending on the mass of the exchanged meson and a short range part,
mainly responsible for the good description of the baryon spectra. We calculate
the NN potential in the adiabatic approximation as a function of Z, the
separation distance between the centres of the two three-quark clusters. The
orbital part of the six-quark states is constructed either from the usual
cluster model states or from molecular orbital single particle states. The
latter are more realistic, having proper axially and reflectionally symmetries.
In both cases the potential presents an important hard core at short distances,
explained through the dominance of the [51]{FS} configuration. However in the
molecular orbital basis the core is less repulsive, as a consequence of the
fact that this basis gives a better upper bound for the energy of the six-quark
system. We calculate the potential for the 3S1 and 3S0 channels with two
different parametrizations. We find a small (few MeV) attractive pocket for one
of these parametrizations. A middle range attraction is simulated by the
addition of a sigma-meson exchange interaction between quarks, of a form
similar to that of the pseudoscalar meson exchange. The present study is an
intermediate, useful step towards dynamical calculations based on the
resonating group method.
