Nonadiabatic effects in molecular adiabatic systems: Application to linear plus quadratic E⊗e system

In this publication I treat two subjects both connected to electronic nonadiabatic transitions. The first is related to the general single-state Born–Oppenheimer equation. Such an equation was recently derived by Baer and Englman [Chem. Phys. Lett. 265, 105 (1997)]; here it is derived again in a different and more instructive way. The second is related to the “linear plus quadratic E⊗e system”. For this system we derive the adiabatic–diabatic-transformation (ADT) angle [Chem. Phys. Lett. 35, 112 (1975)] and show that it is identical to the phase factor obtained by Zwanziger and Grant [J. Chem. Phys. 87, 2734 (1987)].