A researcher records the infrared spectrum of gaseous methanol at moderate resolution
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A researcher records the infrared spectrum of gaseous methanol at moderate resolution. A baseline drift causes the plotted absorbance to slope upward from left to right. Superimposed on this drift are two partially overlapping absorption bands, described as follows.
Band X: apparent maximum at 3.4 µm with a shoulder at 3.5 µm
Band Y: apparent maximum at 1.05 cm with several narrow, evenly spaced sub-peaks
After subtracting the sloping baseline digitally, the corrected intensities reveal the true peak maxima noted above.
(a) Convert the wavelengths of Band X and Band Y into wavenumbers (cm−1). Show your work.
(b) Based on the corrected peak positions, determine which band corresponds to vibrational transitions and which corresponds to rotational transitions. Provide two distinct pieces of evidence from the numerical and qualitative information that support your determination.
(c) The overlapping nature of Band X prevented the precise determination of its bandwidth. Propose a modification to the experimental setup that would reduce overlap of vibrational bands in future measurements, and justify your proposal chemically.