  Polar molecules in selected quantum states can be guided, decelerated and
trapped using electric fields created by microstructured electrodes on a chip.
Here we explore how non-adiabatic transitions between levels in which the
molecules are trapped and levels in which the molecules are not trapped can be
suppressed. We use 12-CO and 13-CO (a 3-Pi(1), v=0) molecules, prepared in the
upper Lambda-doublet component of the J=1 rotational level, and study the trap
loss as a function of an offset magnetic field. The experimentally observed
suppression (enhancement) of the non-adiabatic transitions for 12-CO (13-CO)
with increasing magnetic field is quantitatively explained.
