Canonical perturbation theory for highly excited dynamics

International audienceThis article proposes an unified presentation of recent results dealing with canonical perturbation theory (also called the contact transformation method in the quantum mechanical context), which shows how the theory is best handled for investigating the highly excited dynamics of small molecules. The following systems are successively addressed: (i) semi-rigid molecules (one electronic surface, one minimum), (ii) floppy molecules (one electronic surface, several minima), and (iii) non-Born–Oppenheimer dynamics (several interacting electronic surfaces). The perturbative Hamiltonians obtained from the proposed procedures are checked against exact calculations performed on ab initio surfaces (HCP and HCN) and model Hamiltonians