1. Lecture 31 Exam II Results

2. Lecture 31 Molecules and bonding
Why do atoms combine together to form molecules, and what forces/concepts
control the way this happens?
How do molecules behave?

3. Lecture 31 Molecules and bonding
The Morse Potential is useful for describing vibrations because it does include
anharmonic effects, and it more closely represents the real potential than
a pure harmonic potential

4. Lecture 31 UV-Visible spectroscopy

5. Lecture 31 Rotational/Vibrational Excitations
Evib = (n+1/2) hbar w
Erot = l(l+1) hbar2/2I

6. Lecture 31 Rotational/Vibrational Excitations
FTIR spectra of tissue from Normal and Tumor cells in human lungs

7. Lecture 31 Rotational/Vibrational Excitations

8. Lecture 32 Stimulated emission

9. Lecture 32 “Forbidden Transitions”
Transitions we have called “forbidden” (i.e. disobey a selection rule) really are simply less likely to occur than the ones that follow the selection rules. This can lead to “metastable states” that last a reasonably long period of time. Having such states allows one to create a “population inversion” (where the excited state is more populated than the lower energy state).

10. Lecture 32 “4-level system for lasers”
In this scheme you avoid the process where by the coherent photons get absorbed by a transition from the ground state back up to the metastable state.

11. Lecture 32 “He-Ne laser energy scheme”
In this scheme you excite the Helium atoms directly, and then use those atoms to excite Neon atoms that perform the lasing. Fig. on the right is from:
Note that the excited He states are not populated directly but they are metastable (why?).

12. Lecture 32 Laser

13. Lecture 32 “Free Electron Lasers”
Strictly speaking, these devices use “undulator” magnets rather than “wigglers” (the difference is only technical and has to do with the ratio of the electron’s cyclotron frequency (eB/m) to the frequency c/lu (where lu is the undulator’s spatial period). If this ratio is small, you get coherent effects.

14. Lecture 33 “X-ray sources through the ages”
From a talk on inverse Compton x-ray sources by David Moncton, founding director of the Advanced Photon Source (shown below)

15. Building a more complex molecule
Isolated impurities
From E. A. Moore: “Molecular Modelling and bonding”, Royal Soc. Chem.

16. Building a solid Graphite/Diamond
Isolated impurities
From W. A. Harrison: “Electron Structure” Freeman.

17. Building a Semiconductor
Fill up the states with electrons just like you fill up atomic or molecular states, fill from the lower energy up being careful to abide by Pauli.
The material properties are dominated at by the highest energy states that are occupied.
1/R E
Isolated
atoms
Condensed
Phase
Conduction
Band
Available
States
No States
available
Valence
Band
Conduction band
Localized states near impurities; These control the properties of the semiconductor
Isolated impurities
Valence band