1. Lecture 9 Vibrational Spectroscopy

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

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

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

5. A primitive rule: Molecular spectra - wide bands Atomic spectra - narrow lines

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

8. a1a1 1CH 2 s-str27832782.5 SSgas2781.6 SS a1a1 2CO str17461746.1 VSVSgas1742.3 WW a1a1 3CH 2 scis1500 1500.1 SSgas1499.7 MM b1b1 4CH 2 a-str28432843.1 VSVSgas2866 WW b1b1 5CH 2 rock1249 1249.1 SSgas b2b2 6CH 2 wag1167 1167.3 SSgas Raman IR

9. Frequency Wavenumber

10. Carbon Monoxide in gas

14. Rayleigh scattering No changes!

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

16. Raman scattering