Non-adiabatic transition
 
A adiabatic process is a process without the input or output of heat.
 
Non-adiabatic transitions are transitions between adiabatic states (i.e. Born Opperheimer states) that are close in energy. If these states are close together a small amount of electronic energy change is enough to induce the transition. This energy can be gained from nuclear motion. This energy transfer between electronic and nuclear degrees of freedom is called a non-adiabatic transition.
 
See also:
Adiabatic state
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