Adiabatic and postadiabatic channel description of atom–diatom long-range half-collision dynamics: Interchannel radial coupling for P1 and P2 anisotropy

Abstract

It is shown that the adiabatic channel states of an atom–diatom system with a low-rank interaction anisotropy (proportional to cos γ and cos2 γ) exhibit a nonlocalized nonadiabatic coupling which persists into the strong coupling region. This feature of adiabatic channel states restricts application of the statistical adiabatic channel model (SACM) for processes of complex decomposition and complex formation to low energies. The change of the representation from adiabatic into the postadiabatic (dynamic) one transforms the coupling to a localized form and makes it possible to find conditions for description of the half-collision dynamics in terms of uncoupled dynamic states. This result can be regarded as the extension of the statistical adiabatic channel model beyond its formal limits of applicability provided the adiabatic channel potentials are replaced by the postadiabatic (dynamic) potentials. The obtained results are exemplified by calculation of the capture cross section in the approximation of uncoupled channels.