Recall that for purely rotational transitions to occur, a molecule must have a permanent dipole moment. As a result, homonuclear diatomic molecules (e.g. H2, N2, O2, Cl2) have no purely rotational spectrum. Do homonuclear diatomic molecules have ro-vibrational transitions? (A) Yes. (B) No.

Recall that for purely rotational transitions to occur, a molecule must have a permanent dipole moment. As a result, homonuclear diatomic molecules (e.g. H2, N2, O2, Cl2) have no purely rotational spectrum. Do homonuclear diatomic molecules have ro-vibrational transitions? (A) Yes. (B) No. The dipole moment of the molecule does not change during vibration or rotation.

Vibration-rotation coupling describes an effect that vibrational excitation changes rotational energy levels. How does vibrational excitation change rotational energies? (A) Higher v → higher Erot(J) (B) Higher v → lower Erot(J)

Vibration-rotation coupling describes an effect that vibrational excitation changes rotational energy levels. How does vibrational excitation change rotational energies? (A) Higher v → higher Erot(J) (B) Higher v → lower Erot(J), because if v increases, <r> increases, so I increases → Erot decreases

Centrifugal distortion has an effect on rotational energy levels. How are rotational transitions with DJ = +1 affected? (A) Higher J → higher DErot(JJ+1) (B) Higher J → lower DErot(JJ+1)

Centrifugal distortion has an effect on rotational energy levels. How are rotational transitions with DJ = +1 affected? (A) Higher J → higher DErot(JJ+1) (B) Higher J → lower DErot(JJ+1) Correct! Centrifugal distortion leads to an increase in bond lengths at higher J values, so I increases at higher J, so DErot(JJ+1) decreases.