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Understanding Vibrational Spectroscopy: Energy Levels and Scattering Phenomena

This lecture explores the fundamentals of vibrational spectroscopy, focusing on the absorption of photons at specific wavelengths. Key concepts include the transition from ground to excited states, the impact of temperature on spectral width, and the differences between molecular and atomic spectra. The principles of Doppler effects, energy levels in molecules, and the distinctions between ideal and real oscillators are discussed, along with the phenomena of Rayleigh and Raman scattering, highlighting energy changes during molecular interactions.

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Understanding Vibrational Spectroscopy: Energy Levels and Scattering Phenomena

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  1. Lecture 9 Vibrational Spectroscopy

  2. Only photons of one specified wavelength are absorbed Excited state Ground state

  3. Width Velocity of a particle >1000 m/s Doppler Speed of light 300,000,000 m/s collisions Approximately as Doppler Both effects increase with the temperature and decrease with the size of the molecule/atom Width is around 0.01-0.001 nm in visible area Multiple energy levels

  4. Energy levels of excited state Energy sublevels Energy levels of ground state

  5. A primitive rule: Molecular spectra - widebands Atomic spectra - narrowlines

  6. 1 - ideal (harmonic) oscilator Dissociation energy 2 - real (anharmonic) oscilator Energy level/ vibrational quantum number

  7. IR Raman

  8. Frequency Wavenumber

  9. Carbon Monoxide in gas

  10. Rayleigh scattering No changes!

  11. Raman scattering Escaping photon has smaller energy because the molecule did not return to the ground state

  12. Raman scattering Raman scattering

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