diabatic

Diabatic is an adjective used across sciences to describe processes or states that involve exchange of heat with a surrounding system. It stands in contrast to adiabatic, in which no heat is exchanged; a diabatic change means the system absorbs or releases heat from its environment, altering temperature, phase, or internal energy beyond work alone.

In thermodynamics and physical chemistry, a diabatic process is any process with nonzero heat transfer (q ≠ 0). Examples include heating a gas by contact with a hot wall, melting or vaporizing a substance, or chemical reactions that release or absorb heat.

In atmospheric science, diabatic heating refers to heat added to or removed from air parcels by processes such as radiative transfer, conduction, and the release or absorption of latent heat during phase changes. Diabatic effects are central to convection, storm development, and regional climate, and are modeled alongside adiabatic processes that assume no heat exchange during vertical motion.

In quantum chemistry, the term diabatic refers to a set of electronic states chosen so their dependence on nuclear coordinates is simple, especially near avoided crossings, to simplify nonadiabatic dynamics. The alternative adiabatic representation follows electronic eigenstates that change with geometry and can produce large derivative couplings. Diabatic states are connected by a coupling term that governs transitions between surfaces, a concept used in models like Landau–Zener theory.