CHEMISTRY · Multi-part · A Level · Chemistry · Organic analysis and spectroscopy · Organic analysis and spectroscopy
Problem
The gas carbon monoxide, CO, shows three prominent absorption features that chemists use to probe its structure:
• Feature A: a set of closely spaced lines centered at 1.15cm−1 (given as wavenumber)
• Feature B: a strong band at 2145cm−1 (wavenumber)
• Feature C: a broad absorption at 150 nm (wavelength)
Respond to the following prompts. All work must be shown and all answers must include correct units. Use any constants supplied on the AP reference sheet.
(1) Convert the positions of Features A and B from wavenumber (cm−1) to wavelength in meters. Show your calculations.
(2) Rank Features A, B, and C in order of increasing photon energy. Explain the reasoning that leads to your ranking.
(3) For each feature, identify whether the corresponding transition in CO is rotational, vibrational, or electronic. Cite evidence from your calculations or reasoning to support each identification.
(4) Discuss how the separation in energy between Features A and B relates to the relative spacing of rotational and vibrational energy levels in diatomic molecules like CO.