For each excited electronic state, either electron spin configuration is possible so that there will be two sets of energy levels (see Figure 9).
Instead, an adiabatic electronic state representation was used in the electronically adiabatic regime.
Thus, in the EPT mechanism with adiabatic ET, the PT process occurs on an adiabatic electronic state, i.e., it is electronically adiabatic.
Both rotational and vibrational energies superimpose on an electronic state.
The molecule then undergoes an electronic state decay back to one of the vibrational states associated with the lower electronic state.
Upon colliding, a molecule can thus be transformed into a different electronic state whose energy minimum may lie lower or higher than its previous electronic state.
Each distinct energy corresponds to an electronic state of the molecule.
Subsequently it can undergo vibrational energy loss to end up in the lowest vibrational state of the 1Σ+ electronic state.
A molecule in a given electronic state will simultaneously possess discrete amounts of rotational and vibrational energies.
For a collection of molecules that are in a particular MO or electronic state, there will be a distribution among the accessible vibrational and rotational states.
Thus, the total energy of a molecule is coarsely defined by its electronic state and more finely by its vibrational state.
