  Exclusive diffractive processes on the nucleon are investigated within a
model in which the quark-nucleon interaction is mediated by Pomeron exchange
and the quark substructure of mesons is described within a framework based on
the Dyson-Schwinger equations of QCD. The model quark-nucleon interaction has
four parameters which are completely determined by high-energy $\pi N$ and $K
N$ elastic scattering data. The model is then used to predict vector-meson
electroproduction observables. The obtained $\rho$- and $\phi$-meson
electroproduction cross sections are in excellent agreement with experimental
data. The predicted $q^2$ dependence of $J/\psi$-meson electroproduction also
agrees with experimental data. It is shown that confined-quark dynamics play a
central role in determining the behavior of the diffractive, vector-meson
electroproduction cross section. In particular, the onset of the asymptotic
$1/q^4$ behavior of the cross section is determined by a momentum scale that is
set by the current-quark masses of the quark and antiquark inside the vector
meson. This is the origin of the striking differences between the $q^2$
dependence of $\rho$-, $\phi$- and $J/\psi$-meson electroproduction cross
sections observed in recent experiments.
