  A theoretical study of the intense-field single ionization of molecular
hydrogen or deuterium oriented either parallel or perpendicular to a linear
polarized laser pulse (400 nm) is performed for different internuclear
separations and pulse lengths in an intensity range of $(2-13)\times10^{13} $W
cm$^{-2}$. The investigation is based on a non-perturbative treatment that
solves the full time-dependent Schr\"odinger equation of both correlated
electrons within the fixed-nuclei and the dipole approximation. The results for
various internuclear separations are used to obtain the ionization yields of
molecular hydrogen and deuterium in their ground vibrational states. An atomic
model is used to identify the influence of the intrinsic diatomic two-center
character of the problem.
