Coupled-Channels Quantum Theory of Electronic Flux Density in Electronically Adiabatic Processes: Application to the Hydrogen Molecule Ion

This article presents the results of the first quantum simulations of the electronic flux density (j e ) by the “coupled-channels”(CC) theory, the fundamentals of which are presented in the previous article [Diestler, D. J. J. Phys. Chem. A 2012, DOI: 10.1021/jp207843z]. The principal advantage of the CC scheme is that it employs exclusively standard methods of quantum chemistry and quantum dynamics within the framework of the Born–Oppenheimer approximation (BOA). The CC theory goes beyond the BOA in that it yields a nonzero j e for electronically adiabatic processes, in contradistinction to the BOA itself, which always gives j e = 0. The CC is applied to oriented H2 + vibrating in the electronic ground state (2Σ g +), for which the nuclear and electronic flux densities evolve on a common time scale of about 22 fs per vibrational period. The system is chosen as a touchstone for the CC theory, because it is the only one for which highly accurate flux densities have been calculated numerically without invoking the BOA [Barth et al, Chem. Phys. Lett. 2009, 481, 118]. Good agreement between CC and accurate results supports the CC approach, another advantage of which is that it allows a transparent interpretation of the temporal and spatial properties of j e .