複選題

21. In ultrafast photochemical processes, molecules are often excited by femtosecond laser pulses to electronically excited states, followed by rapid nuclear motion and electronic relaxation. In such situations, the validity of the Born–Oppenheimer approximation (BOA) becomes a central issue. The BOA exploits the large mass difference between nuclei and electrons to simplify the molecular Schrödinger equation by separating electronic and nuclear motions. Which of the following statements regarding the Born–Oppenheimer approximation (BOA) are correct?
(A) The BOA assumes that electrons respond instantaneously to nuclear motion due to their much smaller mass.
(B) Within the BOA, the total molecular wavefunction is expressed as a product of an electronic wavefunction and a nuclear wavefunction.
(C) Zero-point vibrational energy is neglected in the BOA.
(D) Immediately after vertical photoexcitation, the BOA is typically valid because the nuclear geometry has not yet changed.


(E) Within the BOA, ultrafast population transfer between different electronic states can be fully described without considering the interaction between nuclear motion and electronic states.