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IR Spectroscopy

IR Spectroscopy . CHM 411 Suroviec Spring 2013. I. Theory of IR Spectroscopy. Frequency of absorbed radiation is the molecular vibration frequency responsible for absorption process – which is directly proportional to wavenumber. A. Dipole Moment. HCl

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IR Spectroscopy

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  1. IR Spectroscopy CHM 411 Suroviec Spring 2013

  2. I. Theory of IR Spectroscopy • Frequency of absorbed radiation is the molecular vibration frequency responsible for absorption process – which is directly proportional to wavenumber

  3. A. Dipole Moment • HCl Charge distribution around molecule is not symmetrical and therefore has a dipole moment

  4. B. Rotation and Vibrational Transitions • Rotational • Vibrational

  5. C. Types of Molecular Vibrations • The relative positions of atoms in a molecule are not fixed but fluctuate continuously as a consequence of a multitude of different types of vibrational and rotational allowed states around the bonds in the molecule

  6. II. Vibrational Modes • It is possible to deduce the number and kinds of vibrations in simple diatomic and triatomic molecules

  7. A. Motion of a molecule • Need to consider: • Motion of a molecule through space (translational) • Rotation around center of gravity • Individual vibrations

  8. B. Vibrational Coupling • Energy of vibrations and wavelength of absorption is influenced by several factors: • Strong coupling between stretching vibrations only occurs when there is an atom in common to the 2 vibrations • Interaction between bending vibrations requires a common bond between vibrational groups • Coupling between stretching and bending vibrations can occur if stretching bond forms one side of an angle that varies • No interaction between groups separated by 2 or more bonds

  9. Example: CO2

  10. Example: H2O

  11. III. Instrumentation A. ATR

  12. B. FTIR

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