Time-dependent molecular fields: The derivation of wave equations

This lecture is based on studies given in Int. J. Quantum Chem. 114, 1645 (2014) and Molec. Phys. 114, 227 (2016) and presents a theory related to the possibility to induce a novel field – called the molecular field. This field is produced via the interaction of an external electric field and a molecular system. Assuming the molecular system is made up of two coupled adiabatic states, the theory leads from one spatial curl equation, two space-time curl equations and a space-time divergence equation to a set of decoupled wave equations usually encountered for fields. In the present study, wave equations are derived for an external field with a high intensity and a short duration. For this situation, the study reveals that the just mentioned interaction creates two fields that coexist within a molecule: one is just an initial scalar field essentially identical to the original external electric field and the other, a vectorial field, produced by (two) field dressed non-adiabatic coupling terms (NACT). In addition, we mention that the wave velocities related to these two fields are identical to the wave velocity, v, of the external field.