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Lecture 9

Lecture 9. Vibrational Spectroscopy. Only photons of one specified wavelength are absorbed. Excited state. Ground state. 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

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Lecture 9

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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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