1. 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.

2. 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.

3. 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)

4. 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

5. 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)

6. 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.