  We present a theory for rigorous quantum scattering calculations of
probabilities for chemical reactions of atoms with diatomic molecules in the
presence of an external electric field. The approach is based on the fully
uncoupled basis set representation of the total wave function in the
space-fixed coordinate frame, the Fock-Delves hyperspherical coordinates and
adiabatic partitioning of the total Hamiltonian of the reactive system. The
adiabatic channel wave functions are expanded in basis sets of hyperangular
functions corresponding to different reaction arrangements and the interactions
with external fields are included in each chemical arrangement separately. We
apply the theory to examine the effects of electric fields on the chemical
reactions of LiF molecules with H atoms and HF molecules with Li atoms at low
temperatures and show that electric fields may enhance the probability of
chemical reactions and modify reactive scattering resonances by coupling the
rotational states of the reactants. Our preliminary results suggest that
chemical reactions of polar molecules at temperatures below 1 K can be
selectively manipulated with dc electric fields and microwave laser radiation.
