What are stationary states in quantum mechanics and how do they contribute to the understanding of the behavior of particles in a system?

Stationary states in quantum mechanics are states in which a particle's energy remains constant over time. These states are important because they provide a framework for understanding the behavior of particles in a system. By studying stationary states, scientists can predict the probabilities of different outcomes when particles interact with each other or with their environment. This helps in explaining the behavior of particles in a system and how they evolve over time.