PHY 113 Lecture Notes - Lecture 4: Absorption Spectroscopy, Spectroscopy, Photon
9 Jun 2018
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Chapter 4 Spectroscopy
Units of Chapter 4
4.1 Spectral Lines
4.2 Atoms and Radiation The Hydrogen Atom
The Photoelectric Effect
4.3 The Formation of Spectral Lines 4.4 Molecules
4.5 Spectral-Line Analysis
4.1 Spectral Lines
Spectroscope: Splits light into component colors
Emission lines: Single frequencies emitted by particular atoms
Emission spectrum can be used to identify elements
Absorption spectrum: If a continuous spectrum passes through a cool gas, atoms of the gas
will absorb the same frequencies they emit
An absorption spectrum can also be used to identify elements. These are the emission and
absorption spectra of sodium:
Kirchhoff’s laws:
• Luminous solid, liquid, or dense gas
produces continuous spectrum
• Low-density hot gas produces emission
spectrum
• Continuous spectrum incident on cool, thin gas produces absorption spectrum
Kirchhoff’s laws illustrated
4.2 Atoms and Radiation
Existence of spectral lines required new model of atom, so that only certain amounts of
energy could be emitted or absorbed
Bohr model previously only allowed certain orbits for the electron
Emission energies correspond to energy differences between allowed levels
Modern model has electron “cloud” rather than orbit
More Precisely 4-1: The Hydrogen Atom
Energy levels of the hydrogen atom, showing two series of emission lines:
The energies of the electrons in each orbit are given by:
The emission lines correspond to the energy differences
Hydrogen is the most abundant element in the universe. So these energies show up a LOT in
astronomy.
(Often in absorption)
“Lyman” lines:
transitions from something n=1 Lyman α n=2 to n=1
“Balmer” lines:
transitions from something n=2
The Photoelectric Effect (recap)
When light shines on metal, electrons can be emitted
• Frequency must be higher than minimum, characteristic of material
• Increased frequency—more energetic electrons
• Increased intensity—more electrons, same energy
Photoelectric effect can only be understood if light behaves like particles
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Document Summary
4. 3 the formation of spectral lines 4. 4 molecules. Emission lines: single frequencies emitted by particular atoms. Emission spectrum can be used to identify elements. Absorption spectrum: if a continuous spectrum passes through a cool gas, atoms of the gas will absorb the same frequencies they emit. An absorption spectrum can also be used to identify elements. These are the emission and absorption spectra of sodium: Kirchhoff"s laws: luminous solid, liquid, or dense gas produces continuous spectrum, low-density hot gas produces emission spectrum, continuous spectrum incident on cool, thin gas produces absorption spectrum. Existence of spectral lines required new model of atom, so that only certain amounts of energy could be emitted or absorbed. Bohr model previously only allowed certain orbits for the electron. Emission energies correspond to energy differences between allowed levels. Modern model has electron cloud rather than orbit. Energy levels of the hydrogen atom, showing two series of emission lines:
