Kinetics and dynamics for chemical reactions in gas phase

A deep understanding of molecular reactions is a challenging task since the range of time and energy covered implies a wide and dense grid for the numerical representation of the reactive Hamiltonian. For a computational chemist, the accurate prediction of its value starting from the definition of reactants and products is fascinating and demanding, but can be extremely useful for further investigation and optimization problems. Several methods, all derived by the Transition State Theory, have been developed to avoid the computational cost of the Hamiltonian representation on a large, multidimensional grid; we investigate these strategies both in the time and energy domain to explore the advan- tages and drawbacks of these reciprocal spaces. Since we want to increase the range of applicability of the calcula- tion of thermal rate constants to medium size molecules, which can have floppy geometries with low frequency modes, we introduce a dedicated treatment of such modes based on the Intrinsic Reaction Path of Fukui. In Part i, we introduce the theoretical instrument used to perform our calculation, both in energy and time domain; Part ii is devoted to the presentation of the applications, mainly focused on current issues in astrochemical studies. Appendices treat specific topics, like Möller operators, essential for the comprehension of the theory but too long to be inserted in Part i.