Vibrational excitation of molecules in the gas phase or embedded in matrices by ab initio molecular dynamics

This book is focused on is the vibrational excitation of one given molecule, and the subsequent dynamics that occurs. During this book, the introduction of vibrational excitation in normal modes for two different prototypical examples has been studied: in condensed phase illustrated with a molecule of Formic Acid (FA) embedded in an argon matrix and in gas phase illustrated with the (Cl-...NMA)Ar cluster. In both cases, we are interested in the "correct" preparation of initial conditions for DFT-MD dynamics (classical nuclei), and in following the evolution with time of the energy in the normal modes of the molecules illustrated by the evolution of the quantum number ni of given normal modes. The manuscript of the thesis is organized as follows : . chapter 2: basis of the theoretical methods used (DFT and VDOS); . chapter 3: presentation of the normal mode sampling of initial conditions; . chapter 4: description of the theoretical methods to follow quantum number evolution; . chapter 5: study of vibrational dynamics of Formic Acid embedded in an argon matrix; . chapter 6: study of vibrational dynamics of (Cl-...NMA)Ar clusters.