Vibrational-rotational spectroscopy is an important technique used to characterize molecular characteristics such as bond length and fundamental vibrational frequency.  In the typical undergraduate laboratory, students gain experience with this technique by taking and analyzing the vibrational-rotational spectrum of HCl.  However, depending on how the lecture and laboratory parts of physical chemistry course are structured, the laboratory experiment is often far removed in time from the discussion of the technique in lecture.  In this approach, students take a vibrational-rotational spectrum of HCl with sufficient precision to see peaks for H<sup>35</sup>Cl and H<sup>37</sup>Cl.  The guided inquiry activity leads students through a theoretical understanding of pure rotational spectroscopy, pure vibrational spectroscopy, and vibrational-rotational spectroscopy.  The activity then guides the students in how to assign beginning and final rotational levels to each peak in their experimental spectrum and how to analyze their data to determine the rotational constants for the ground and first excited vibrational states.  The combination of guided inquiry with the laboratory experiment links the theoretical aspects of this technique directly to the practical data analysis.

Using a guided inquiry and experimental approach to teaching vibrational-rotational spectroscopy

253rd National Meeting (2017)

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