  Carrier envelope phase (CEP) stabilized pulses of intense 800 nm light of 5
fs duration are used to probe the dissociation dynamics of dications of
isotopically-substituted water, HOD. HOD$^{2+}$ dissociates into either H$^+$ +
OD$^+$ or D$^+$ + OH$^+$. The branching ratio for these two channels is
CEP-dependent; the OD$^+$/OH$^+$ ratio (relative to that measured with
CEP-unstabilized pulses) varies from 150% to over 300% at different CEP values,
opening prospects of isotope-dependent control over molecular bond breakage.
The kinetic energy released as HOD$^{2+}$ Coulomb explodes is also
CEP-dependent. Formidable theoretical challenges are identified for proper
insights into the overall dynamics which involve non-adiabatic field ionization
from HOD to HOD$^+$ and, thence, to HOD$^{2+}$ via electron rescattering.
