Atomic and molecular collisions

Interactions in which atoms or molecules approach and scatter, exchange energy, or react. Their outcomes depend on relative motion and the forces acting between the particles.

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Scattering theory: The framework for predicting how waves or particles change direction and state after interacting with a target. It describes collision outcomes through incoming and outgoing particle states.
Reduced mass: The effective mass that replaces two interacting masses in their relative-motion problem. It determines how much relative kinetic energy corresponds to a given collision speed.
Chemical kinetics: The study of how fast chemical reactions occur and how their rates depend on conditions. Collision rates and reaction probabilities provide a microscopic basis for reaction-rate laws.
Elastic scattering: Scattering in which total kinetic energy is conserved and particles retain their internal states. It contrasts with collisions that transfer internal energy or alter chemical species.
Potential energy surface: A function giving a molecular system’s potential energy as its nuclei move through different arrangements. Its shape governs how colliding atoms and molecules are deflected or driven toward reaction.
Center-of-momentum frame: A reference frame in which the total momentum of a system is zero. Collision energy and scattering angles are often simplest to describe in this frame.
Maxwell–Boltzmann distribution: The distribution of particle speeds or energies in a classical gas at thermal equilibrium. It connects single-collision energy dependence to rates averaged over a gas.
Inelastic scattering: Scattering in which particles exchange kinetic and internal energy while conserving total energy. It separates energy-transfer collisions from purely elastic deflection.
Cross section (physics): A measure of the effective area for a specified interaction between particles. Collision cross sections quantify the likelihood of scattering or a particular reaction.
Interatomic potential: A function describing the potential energy between atoms as a function of their separation. It captures the attractive and repulsive forces that shape an atomic encounter.