An air sample collected near a forest fire is analysed by broadband absorption…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
An air sample collected near a forest fire is analysed by broadband absorption spectroscopy. A noisy spectrum is obtained, verbally summarised below.
• Significant peaks appear at 5.0 µm (Peak P), 2.1 µm (Peak Q), and 1.0 cm (Peak R).
• Random high-frequency noise is present across the entire spectrum.
• The baseline shows periodic oscillations attributed to water vapour inside the optical bench.
Answer the following questions regarding the interpretation and improvement of this spectrum.
(a) For each peak, propose the most probable type of molecular transition involved and cite the physical basis for each assignment.
(b) Identify which peak(s) are most likely influenced by water vapour contamination and justify your answer by referencing known absorption characteristics of water.
(c) Design an experimental modification that would both reduce the observed baseline oscillations and improve the signal-to-noise ratio of peaks P, Q, and R. Provide a chemical rationale for how your proposed change addresses each issue.
(d) The investigator wishes to confirm whether Peak Q arises from newly formed carbonyl-containing combustion products. Outline a follow-up spectroscopic test, specifying the region of the spectrum to be probed and the expected outcome that would support this hypothesis.