On the spectral and dynamic effects of near-nodal molecule-EMF coupling arising from permanent dipole moments

The spectral and temporal consequences of a non-zero difference d kj = µ kk - µ jj between the permanent dipole moments µ jj of two states involved in a transition are investigated for two and three-level model molecular systems interacting with a continuous wave laser. The field strengths are such that the molecule–EMF couplings for the systems are near-nodal. The interesting spectral and dynamic effects of near-nodal molecule–EMF couplings are unique to transitions where d kj ≠ 0, relative to d kj = 0. These effects are studied using exact Floquet calculations and analytical solutions in the two-level rotating wave approximation (RWA). The RWA discussion of near-nodal molecule–EMF couplings, how they are achieved, and their effects, is quite general and applies to any two-level model of a dipolar molecule. The actual values of the laser parameters required to achieve a molecule–EMF coupling node depend on the specific molecule under consideration. This is illustrated with explicit twoand three-level molecular models, based on the S0 and S1 states of 1-[p-(N, N -dimethylamino)phenyl]-4-(p-nitrophenyl)-1,3-butadiene. Although the field strengths required to achieve near-nodal couplings are too large for the quantitative application of the analytical results, the two-level RWA solutions are crucial for the qualitative interpretation and prediction of the exact laser–molecule behaviour. The examples illustrate that the near-nodal effects of d kj = 0, as predicted by the two-level RWA and verified by the two- and three-level exact calculations, persist when neighbouring energy levels are present in the model.