We present a theoretical treatment for the single and double ionization of
molecules in strong laser pulses, including the effect of electron correlat
ions. Applied to a model N-2 molecule, our simulations show that double ion
ization occurs via a direct two-electron mechanism at moderate laser intens
ities (N-2 ((h) over bar omega) under right arrow N-2(2+) + 2e(-)) while a
step-by-step sequential ionization process dominates at higher intensity (N
-2 ((h) over bar omega) under right arrow N-2(+) + e(-) ((h) over bar omega
) under right arrow N-2(2+) + 2e(-)). At intermediate intensity, these two
mechanisms have a comparable contribution to the total double-ionization yi
eld. This phenomenon is directly reflected in the spatial distributions of
N-2(+) and N-2(2+) in the focal volume of the laser pulse. In addition we s
how that at high intensity the singly and doubly charged molecular ions are
created in well separated regions of space.