Reaction mechanism is the study of the step-by-step process by which chemical reactions occur. It involves understanding the sequence of elementary steps and the interactions between molecules and atoms during a chemical reaction. By studying reaction mechanisms, researchers can gain insight into the factors that influence reaction rates, selectivity, and outcome, as well as develop new strategies for controlling and optimizing chemical transformations. This area of research plays a crucial role in various fields such as organic chemistry, biochemistry, and materials science.