Dipolar radicals in crossed electric and magnetic fields.

Paramagnetic, dipolar Hund's case-a radicals are considered in the presence of arbitrary, non-collinear combinations of electric and magnetic fields. The field-dependent part of the Hamiltonian is found to exhibit a good quantum number, consisting of the projection of the molecule's total angular momentum along a space-fixed axis that is determined by both the fields and the electric and magnetic dipole moments of the molecule. This quantity remains good even when the fields are non-collinear. Exploiting this feature identifies a set of quantum numbers for the molecule in crossed fields. We dub this set a 'Hund's case-X' basis. [ABSTRACT FROM AUTHOR]