On the nature of intramolecular dephasing processes in polyatomic molecules

Intramolecular dephasing processes in polyatomic molecules are discussed with relation to coherent transient spectroscopy, radiationless transitions, multiphoton molecular processes, and overtone spectroscopy. A distinction is made between proper and improper dephasing processes (PDP, IDP) depending on whether they arise due to changes in populations or not. It is shown that the type of experiment and, consequently, the way we partition the hamiltonian are closely related to this distinction. We consider several experimental and theoretical approaches for studying intramolecular dynamics and discuss under what conditions it is necessary and useful to introduce explicitly dephasing interactions.