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What are the conditions to excite an atom by collision?

  1. Jan 23, 2016 #1
    I know that an atom can become excited in one of two ways: by absorbing some energy from a source of electromagnetic radiation or by colliding with some other particle—another atom, for example, but my question is about the second part. So I want to know how and in what conditions (pressure, temperature ...) an atom can collide with another atom or even molecule and it causes excitation. Then after the atom's excitation, an electron boost into a higher orbital.

    I exactly mean that I wonder if the atoms or molecules can become excited in low temperature. No matter which atom or molecule, but the question is if it is possible to excite an atom or molecule in a gas system without external source of energy and just when they collide together, or not. If yes what is the conditions.
     
  2. jcsd
  3. Jan 23, 2016 #2
    Within a closed system no extra energy is produced if atoms collide.
    There could be some exchange of energy with one atom gaining energy and the other losing.
    In the extreme case there could be nuclear fusion, but that still doesn't create new energy, it's just a re-arrangement of the energy already existing in the system.
     
  4. Jan 23, 2016 #3

    Andy Resnick

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    This is the process involved in HeNe lasers. The Ne atoms are excited via collisions with electrons created by RF discharge and some excited He atoms collide with Ne atoms, non-radiatively transferring the energy because the two sets of energy levels are nearly coincident. The Ne atom then de-excites via a number of paths, and several of the paths involve laser lines:

    https://upload.wikimedia.org/wikipedia/commons/e/ed/Hene-2.png

    In order for this process to be efficient, the partial pressure of He is about 10 times that of Ne, and the whole lasing medium is kept at low absolute pressure to minimize collisions with the walls of the cavity.
     
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