Advances in spectroscopy and dynamics of small and medium sized molecules and clusters.

Investigations of the spectroscopy and dynamics of small- and medium-sized molecules and clusters represent a hot topic in atmospheric chemistry, biology, physics, atto- and femto-chemistry and astrophysics. Nowadays, outstanding developments, both theoretical and experimental, have been achieved. The most recent results of these achievements are reviewed here. These molecular systems are studied by means of high-resolution spectroscopic techniques in either the frequency or the time domains. However, they still represent complex molecular systems since they may undergo processes that are still not fully understood in sufficient details. Indeed, electronic and nuclear motions may lead to complex features that are observed experimentally. From a theoretical point of view, these features can only be interpreted if the quantum nature of the atomic nuclei is considered together with the possible couplings between nuclear and electronic degrees of freedom. New developments, from both theoretical and experimental sides, are needed for modeling and engineering applications of outstanding importance. Possible future research directions are discussed.