  N$_2$ molecules traveling in pulsed supersonic beams have been excited from
their ${\mathrm{X\,^1\Sigma_{\mathrm{g}}^+}}$ ground electronic state to
long-lived Rydberg states with principal quantum numbers between 39 and 48
using a resonance-enhanced two-color three-photon excitation scheme. The
Rydberg states populated had static electric dipole moments exceeding $5000$ D
which allowed deceleration of the molecules to rest in the laboratory-fixed
frame of reference and three-dimensional trapping using inhomogeneous electric
fields. The trapped molecules were confined for up to 10 ms, with effective
trap decay time constants increasing with principal quantum number, and ranging
from 450$\mu$s to 700 $\mu$s. These observations, and comparison with the
results of similar measurements with He atoms, indicate that the decay dynamics
of the trapped Rydberg N$_2$ molecules are dominated by spontaneous emission
and do not exhibit significant contributions from effects of intramolecular
interactions that lead to non-radiative decay.
