The appearance of intermediate states (also referred to as resonant states) in atomic, molecular and nuclear reactions is considered as the most interesting physical phenomena since the development of the quantum theory in the early thirties of the preceding century. The development of femtosecond lasers has tremendously enhanced the experimental identification of these states in chemical reactions. The main objective of the present work is to develop a unified mathematical formalism for the localization of resonant states in physical and chemical reactions. Numerical examples for the validity of this formalism will be demonstrated.
