  We study the effect of the nuclear-mass ratio in a diatomic molecular ion on
the dissociation dynamics in strong infrared laser pulses. A molecular ion is a
charged system, in which the dipole moment depends on the reference point and
therefore on the position of the nuclear center of mass, so that the
laser-induced dynamics is expected to depend on the mass asymmetry. Whereas
usually both the reduced mass and the mass ratio are varied when different
isotopologues are compared, we fix the reduced mass and artificially vary the
mass ratio in a model system. This allows us to separate effects related to
changes in the resonance frequency, which is determined by the reduced mass,
from those that arise due to the mass asymmetry. Numerical solutions of the
time-dependent Schr\"odinger equation are compared with classical trajectory
simulations. We find that at a certain mass ratio, vibrational excitation is
strongly suppressed, which decreases the dissociation probability by many
orders of magnitude.
