  The ionization of H2 in intense laser pulses is studied by numerical
integration of the time-dependent Schr\"odinger equation for a
single-active-electron model including the vibrational motion. The electron
kinetic-energy spectra in high-order above-threshold ionization are strongly
dependent on the vibrational quantum number of the created H2+ ion. For certain
vibrational states, the electron yield in the mid-plateau region is strongly
enhanced. The effect is attributed to channel closings, which were previously
observed in atoms by varying the laser intensity.
