Excited electronic states and nonadiabatic effects in contemporary chemical dynamics.

摘要: The question of how to describe the crossing molecular electronic states is one most challenging issues in contemporary chemical dynamics. In recent years, fundamental concept conical intersections (CIs) potential energy surfaces (PESs) has emerged, which allows extremely fast and efficient switching a molecule between its excited ground states. CIs are ubiquitous polyatomic molecules. Because they generically allow crossings Born-Oppenheimer (BO) adiabatic PESs, have become crucial mechanistic elements rapidly growing area nonadiabatic chemistry. critical consequence complete breakdown BO approximation. That means that reorganization fast-moving electrons nuclear vibrations must be treated concurrently. Ideally, theoretical description should quantum mechanical this situation. However, because complexity, necessary approximations often make it difficult conclusively predict dynamic behavior large addition, nonunique diabatic representation (describing coupling Hamiltonian) essential avoid singular nature kinetic terms unique representation. This Account describes both challenges some advances studies processes, highlighting results from our work examining static aspects their dynamical consequences. spectroscopic implications Jahn-Teller (JT) pseudo-Jahn-Teller (PJT) complex systems discussed. Our probes underlying details vibronic spectra sizes degrees freedom. necessity extension treatment beyond linear approach addressed. establish highly overlapping band structures due JT PJT CIs, bimodal distribution spectral intensity originates strong coupling, role intermode bilinear progressions bands. Investigations dynamics prototypical naphthalene radical cation were aimed at understanding photostability, lack fluorescence emissions, diffuse interstellar established relaxation through CIs. Simulations interplay relativistic spin-orbit photodetachment spectroscopy ClH(2)(-), conjunction with experimental data, support existence shallow van der Waals well reactive Cl + H(2) PES. These also reveal quenching by relatively coupling. we studied H reaction new perspective explicitly including two split degenerate state. Although individual probabilities show partial sensitivity effects, not important for outputs such as integral cross sections thermal rate constants.