Nonadiabatiska

Nonadiabatiska, or nonadiabatic, processes describe situations in which electronic and nuclear motions in a molecule are strongly coupled and cannot be treated as independent. In the Born-Oppenheimer approximation, nuclei move on a single electronic potential energy surface; nonadiabatic dynamics arise when electronic states interact as nuclei change, leading to transitions between surfaces driven by nuclear motion. These effects are especially important when potential energy surfaces come close or cross, creating strong couplings.

Key concepts include potential energy surfaces, derivative (nonadiabatic) couplings, conical intersections, and vibronic interactions. Transitions between electronic states produced by nuclear motion can cause internal conversion, intersystem crossing, or charge transfer without emission of light. Nonadiabaticity also plays a role in proton-coupled electron transfer and in photochemical reaction pathways that determine product yields.

Methods to study nonadiabatiska dynamics combine theory and experiment. On the theory side, approaches such as fewest-switches surface hopping, multiconfigurational time-dependent Hartree, and other quantum dynamics methods explicitly include couplings between electronic states. Diabatization and calculation of nonadiabatic coupling vectors are common pre-processing steps. Experimentally, ultrafast spectroscopy and pump-probe techniques probe excited-state lifetimes and transition pathways affected by nonadiabatic effects.

Understanding nonadiabatiska dynamics is crucial for photochemistry, photovoltaics, vision chemistry, and catalysis, where controlling excited-state lifetimes and reaction channels depends on managing electronic–nuclear coupling.