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Understanding Spectra: Emission, Absorption, and Light Interaction with Matter

This comprehensive overview explores the fundamentals of light emission and absorption spectra, delving into key topics such as the atomic structure of hydrogen, various spectra types, and the implications of electron transitions. Discussing essential concepts including the Bohr model, blackbody radiation, and the significance of energy transitions, this content highlights how elements emit and absorb different wavelengths of light depending on temperature and electron configurations. Such insights form the cornerstone of spectroscopy and our understanding of the universe.

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Understanding Spectra: Emission, Absorption, and Light Interaction with Matter

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Presentation Transcript

  1. Light EmissionChapter 30

  2. Collimating Lens Imaging Lens Dispersive Element Slit Recording Device Basic Spectrograph

  3. Mercury near Horizon The atmosphere can act like a prism

  4. Continuous Spectrum Source must be HOT and DENSE

  5. Emisson (Bright Line) Spectrum Source must beHOTandTENUOUS

  6. Absorption Spectrum

  7. Continuous Emission Absorption Types of Spectra

  8. He “bullet” Atom Rutherford Scattering Experiments

  9. Hydrogen Atom • Simplest atom • One proton, one electron • Most abundant atom • 90% of the universe is hydrogen

  10. e- Force p Planetary Model Since electron orbits the proton, a force exists.

  11. e- Acceleration p Planetary Model • Force implies acceleration • Accelerating charges emit light • Light carries energy (E = hf)

  12. e- p Planetary Model Electron moves closer to the nucleus since it requires less energy to be there.

  13. Planetary Model • But the electron is still accelerating • Must still be radiating energy (light) • Must move still closer to the nucleus • Electron will spiral into and collide with the nucleus (in about 10-8 seconds) Atoms do not exist!!

  14. Bohr’s Hypotheses • Stable electron orbits exist where the electron does not lose energy.

  15. Electrons can be here or here but not here p

  16. Bohr’s Hypotheses • Transitions can occur between orbits so long as the electron ends up with the energy of the new level.

  17. 5 4 3 Energy 6563 Å photon 2 Hydrogen Absorption

  18. 5 4 Energy 3 6563 Å photon 2 Hydrogen Emission

  19. Hydrogen Atom 5 4 -e 434 nm 3 2 656 nm -e 1 -e +P 486 nm 410 nm -e -e 400 nm 700 nm

  20. Emission andAbsorption Lines • Lines come from electron transitions • Energy change either comes from (absorption) or is given to (emission) photon. E • Photon energy  Frequency • E = hf • Frequency  1/(Wavelength) • f = c/l • Wavelength means COLOR

  21. Brackett (Far IR) Paschen (IR) 4 3 Balmer (VIS) 2 1 Lyman (UV) Hydrogen Spectrum Energy

  22. Aluminum Argon Calcium Carbon Helium Hydrogen Iron Krypton Magnesium Neon Nitrogen Oxygen Sodium Sulfur Xenon

  23. Atomic Spectra Review

  24. 400nm 500nm 600nm 700nm Continuous Radiation • How bright is the continuous spectrum at different colors? • How does a perfect light source emit its light?

  25. Early Experiments Blackbody Radiation Darken inside with carbon black Measure radiation that emerges from hole

  26. Blackbody Radiation Vis UV IR

  27. Changes with Temperature Visible * 7000 K * 6000 K * 5000 K

  28. Blackbody Radiation • Everything in nature emits light • The type of light emitted depends on the temperature of the source • The walls of this room • IR • Stars • Visible and UV • The Corona of the Sun (2,000,000 K) • X-rays

  29. Wien’s Displacement Law • The wavelength of the peak of the blackbody curve is inversely proportional to the temperature. lmax 1/T fmax  T Cool stars are red - hot stars are blue

  30. Visible Photon UV Photon Visible Photon Fluorescence

  31. Visible Photon UV Photon Visible Photon Phosphorescence Let’s wait here

  32. LASERS Light Amplification by Stimulated Emission of Radiation • Monochromatic: one specific wavelength (color) of light • Coherent: every wave is moving in step • Directional: beam is tight, strong and concentrated

  33. “Pumping”

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