Fine structure, alignment, and orientation of 32S16O and 16O18O molecules in congruent electric and magnetic fields

We analyze the eigenproperties of the SO and 16O18O ground-state (3Σ) molecules in congruent electric and magnetic fields. The energy levels are found to exhibit avoided crossings for states with the same projection M of the total angular momentum on the common axis of the fields. The avoided crossings are due to a first-order Stark effect which connects intersecting levels of aligned Zeeman states of opposite parity and makes them strongly oriented. We exemplify the enhancement of orientation and other generic features of the combined electric and magnetic dipole interaction in polar 3Σ molecules by evaluating the expectation values of the orientation and alignment cosines as a function of field-strength parameters for a selection of states with |M|⩽5. The molecular states created by the congruent fields can be used to state-select and focus molecules, to orient the molecular axis in studies of collision stereodynamics, to facilitate assignments of spectral transitions, and in molecular trapping. In particular, we found that mixed-isotope O2 and 17O2 are the only chalcogen molecules which are suitable for spatial trapping in a static trap, owing to their rotational ground state which correlates with a low-field seeking Zeeman state.