Ellis and Randy Are Looking at a Molecular Absorption Spectrum

question 40

Multiple Choice

Ellis and Randy are looking at a molecular absorption spectrum. The spectral lines appear to fall into two groups with a gap in the middle. Ellis says that this must be an absorption spectrum for transitions between the v = 0 and v = 1 vibrational states of a diatomic molecule. Randy says the gap in the middle must occur because a ΔJ = 0 transition is forbidden. Which one, if either, is correct, and why?

• A) Ellis, because rotational levels are separated by greater energy differences than vibrational levels.
• B) Randy, because rotational levels are separated by greater energy differences than vibrational levels.
• C) Ellis, because the ΔJ = 0 transition is the most prominent spectral line in transitions between vibrational levels.
• D) Neither, because rotational levels are separated by greater energies that vibrational levels and ΔJ = 0 transitions are not forbidden.
• E) Both, because vibrational levels are separated by greater energy differences than rotational levels and ΔJ = 0 transitions are forbidden.