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Unit 7: Spectroscopy I: Rotational and Vibrational Spectra   This is the first unit of the spectroscopy portion of the course.  When electromagnetic waves interact with matter, the outcome of the interaction depends on both the nature of the molecule and the frequency of the interacting light.  Infrared (IR) light usually causes atoms within a molecule to vibrate and/or rotate.  In this unit, you will learn how to correlate the electronic structure of molecules and their symmetry to vibrational and rotational phenomena.

Unit 7 Time Advisory
This unit will take you 18 hours to complete.

☐    Subunit 7.1: 6 hours

☐    Subunit 7.2: 6 hours

☐    Subunit 7.3: 6 hours

Unit7 Learning Outcomes
Upon successful completion of this unit, the student will be able to:

  • Explain the interaction of electromagnetic radiations with matter.
  • Explain the origins of line spectra.
  • Explain rotational vibration in terms of simplified systems such as rigid rotors.
  • Explain the difference between IR and Raman spectroscopy.
  • Apply molecular symmetry to predict vibrational modes.
  • Describe how vibrational-rotation spectra originate.

7.1 Molecular Spectroscopy and Symmetry  

  • Reading: Southern Methodist University: Professor Werner Horsthemke’s “Physical Chemistry II Lecture Notes” Link: Southern Methodist University: Professor Werner Horsthemke’s “Physical Chemistry II Lecture Notes” (PDF)

    Instructions: For Professor Horsthemke’s notes, click on the link above, scroll down the webpage to the “Lecture Notes” section, and click of the “PC2Set7.pdf” link.  This set of notes will open as a PDF file, and you can read the entire set.  Pay close attention on how the shape of the molecule results in different types of vibration.  Studying this resource should take approximately 6 hours to complete.

    Terms of Use: Please respect the copyright and terms of use on the webpage displayed above.

7.2 Pure Rotational Spectroscopy  

  • Reading: Everyscience.com’s “Molecular Rotation” Link: Everyscience.com’s “Molecular Rotation” (HTML)
     
    Instructions: Please click on the link above to access the Everyscience.com website.  Then, select the links to and read the webpages for “An Introduction to Spectroscopy” through “Rotational Raman Spectra.”  Studying this resource should take approximately 6 hours to complete.  Note that this resource also covers the material you need to know for subunits 7.2.1–7.2.9.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

7.2.1 An Introduction to Spectroscopy   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 1 to receive an introduction to spectroscopy.

7.2.2 Intensities of Spectral Lines   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 2 to learn about the intensity of spectral lines.

7.2.3 Introduction to Rigid Rotors   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 3 to receive an introduction to rigid rotors.

7.2.4 Spherical Rotors   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 4 to learn about spherical rotors.

7.2.5 Symmetric Rotors   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 5 to learn about symmetric rotors.

7.2.6 Linear and Asymmetric Rotors   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 6 to learn about linear and asymmetric rotors.

7.2.7 Centrifugal Distortion   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 7 to learn about centrifugal distortions.

7.2.8 Rotational Selection Rules   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 8 to learn about rotational selection rules.

7.2.9 Rotational Raman Spectra   Note: This subunit is covered by the readings assigned beneath subunit 7.2.  In particular, please focus on topic 9 to learn about rotational Raman spectra.

7.3 Vibrational Spectroscopy  

  • Reading: Everyscience.com’s “Vibrational Spectroscopy” Link: Everyscience.com’s “Vibrational Spectroscopy” (HTML)
     
    Instructions: Please click on the link above and then select the links from “Molecular Vibrations” through “Vibrational Raman Spectra of Diatomic Molecules.”  Read all six web pages.  Studying this resource should take approximately 2 hours to complete.  Note that this reading also covers the material you need to know for subunits 7.3.1–7.3.5.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: Concordia College: Professor Darin J. Ulness’s “Molecules and Molecular Spectroscopy” Link: Concordia College: Professor Darin J. Ulness’s “Molecules and Molecular Spectroscopy” (PDF)
     
    Instructions: Please click on the link and select the “Old Course Notes” hyperlink to open the PDF file.  Read pages 243–248.  Studying this resource should take approximately 2 hours to complete.  Note that this reading also covers the material you need to know for subunits 7.3.1–7.3.5.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

7.3.1 Molecular Vibrations and Spectroscopy   Note: This subunit is covered by the readings assigned beneath subunit 7.3.  In particular, please focus on Professor Darin J. Ulness’s “Molecules and Molecular Spectroscopy,” sections 17.1 and 17.2, to learn about molecular vibrations and their application to spectroscopy.

7.3.2 Vibrational Selection Rules   Note: This subunit is covered by the readings assigned beneath subunit 7.3.  In particular, please focus on topic 2 in Everyscience.com’s “Vibrational Spectroscopy” to learn about vibrational selection rules.

7.3.3 Anharmonic Oscillation   Note: This subunit is covered by the readings assigned beneath subunit 7.3.  In particular, please focus on topic 3 in Everyscience.com’s “Vibrational Spectroscopy” to learn about anharmonic oscillations.

7.3.4 Vibration – Rotation Spectra   Note: This subunit is covered by the readings assigned beneath subunit 7.3.  In particular, please focus on topic 4 in Everyscience.com’s “Vibrational Spectroscopy” to learn about vibrational-rotation spectra.

7.3.5 Combination Differences   Note: This subunit is covered by the readings assigned beneath subunit 7.3.  In particular, please focus on topic 5 in Everyscience.com’s “Vibrational Spectroscopy” to learn how you can use the method of combination differences to determine the rotational constant of a vibrationally excited state.

7.3.6 Raman Spectroscopy  

  • Reading: Connexions: Courtney Payne and Andrew R. Barron’s “Raman and Surface-Enhanced Raman Spectroscopy” Link: Connexions: Courtney Payne and Andrew R. Barron’s “Raman and Surface-Enhanced Raman Spectroscopy” (HTML)

    Instructions: Please read the entire webpage to learn how particular types of light scattering (Stoke and Anti-stoke) can be used to determine the structure of certain molecules.  Studying this resource should take approximately 0.25 hours to complete.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Assessment: The Saylor Foundation’s “Assessment 11” Link: The Saylor Foundation’s “Assessment 11” (DOC)
     
    Instructions: Complete the attached assessment questions to check your understanding of the material covered thus far. Once you have completed the assessment, you may check your answers against the “Answer Key” (DOC).
     
    Completing this assessment should take approximately 1 hour.