Absorbing and emitting photons
We begin with a large number of these molecules in their ground states.
|A quantum system (a molecule) has the energy levels shown in the diagram at the right. The energies are as follows:
- E0 = 1.1 eV
- E1 = 1.8 eV
- E2 = 3.2 eV
- We want to raise a lot of these molecules to the state labeled E2 by shining light on it.
What wavelength of light should we use?
- If we expose our molecules to a continuous spectrum of light, photons of particularly energies might be absorbed. What energy photons would you expect to absorb? Explain.
- .. If we manage to successfully excite a number of the molecules to the state E2, they can decay
by emitting photons. What energy photons might you expect to see? Explain.
Note to the instructor: Students run into the same problem here that they did at the beginning of the course: getting confused between the value of a quantity (here the energy) and a change in that quantity.
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Page last modified
October 31, 2002: MP07