Non-adiabatic coupling as a frictional force in the formation of H 3 + : a model dynamical study

By treating the non-adiabatic coupling terms (NACTs) in a molecular system as equivalent to a frictional force, the classical equation of motion is solved for a test case of quasi-H3+ along the C2v axis and axes parallel to it, and it is shown that the singular NACTs between the first two excited electronic states slow down the relative motion of the three quasi-ions (H,H,H)+ while approaching each other.