  We theoretically investigate the mechanism of enhanced ionization in
two-electron molecules by analyzing Bohmian trajectories for a one-dimensional
H2 in an intense laser field. We identify both types of ionizing trajectories
corresponding to the ejection from the up-field and down-field cores. The
trajectories of the two electrons are correlated with each other in the former
while correlation is negligible in the latter. The contributions from the two
ionization types, though depending on laser intensity and internuclear
distance, are comparable to each other.
