The relation between atoms' kinetic energy and the energy levels

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Discussion Overview

The discussion revolves around the relationship between the kinetic energy of atoms and the energy levels of their electrons when excited. Participants explore the mechanisms of energy transfer during excitation, whether through radiation or collisions, and the implications for both electronic and kinetic energy. The scope includes theoretical considerations and speculative reasoning about energy transitions and their effects.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions what occurs during atomic excitation and seeks clarification on how energy is distributed between electronic energy levels and the atom's kinetic energy.
  • Another participant suggests that energy transferred during excitation likely contributes to the kinetic energy of the atom, implying a difference between energy levels is involved.
  • A participant speculates that collisions primarily lead to vibrational or rotational transitions rather than electronic transitions, suggesting that significant thermal energy is needed for electronic transitions.
  • In response, another participant challenges this view, arguing that thermal motion can indeed cause electronic transitions, particularly in hot gases.
  • Further discussion highlights examples of hot gases and metals that emit radiation, indicating that thermal energy can lead to radiative emissions, though there is debate about the specifics of energy transfer mechanisms.
  • One participant reiterates the idea that collisions result in vibrational transitions and questions the necessity of nonradiative transitions before electronic relaxation occurs.

Areas of Agreement / Disagreement

Participants express differing views on the role of thermal energy in causing electronic transitions, with some asserting that significant thermal energy is required while others argue that thermal motion can lead to such transitions. The discussion remains unresolved with multiple competing perspectives on the mechanisms involved.

Contextual Notes

There are unresolved assumptions regarding the conditions under which electronic transitions occur and the specific energy transfer processes involved. The discussion also reflects varying interpretations of the relationship between kinetic energy and electronic energy levels.

bentzy
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Regarding the relation between atoms' kinetic energy and the energy levels of their electrons upon excitation:

In other words, what really happens when an atom is excited, either by radiation or by collisions, or otherwise ? What are the mechanisms under which the transferred energy goes to exciting the electronic levels, the atom's kinetic energy as a whole, or both ? in the latter case, which is supposedly the most common case, what's the ratio between the two (elec energy levels & atomic kinetic energy) ? Any elaboration on these aspects will be great.

Thank you, BC
 
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since the energy transferred has to be the difference between some energy levels the difference with the energy of the radiation or the colliding particle is probably transmitted to the kinetic energy of the whole atom.
 
A collision can only result in a vibrational or rotational energy level transition. This is a transfer of kinetic energy. I would speculate (so don't quote me on this) that it would require extremely large amounts of thermal energy to cause an electronic transition as a result of kinetic energy transfer.

By absorbing a photon of near-UV/Vis light, a substance can undergo an electronic transition. When this happens, electrons are promoted to a higher energy level. Between electronic energy levels there are vibrational energy levels, and between vibrational energy levels there are rotational energy levels, and all are quantized. The molecule/particle must undergo nonradiative vibrational transitions in the form of collisions before its promoted electron can "relax" to its ground state. When the electron relaxes, the difference in energy between the excited and ground states is released in the form of a photon. The energy of the emitted photon is always less than the energy of the absorbed photon, due to the nonradiative transitions that occur.

I'm only an undergrad so I hope this helps!
 
You sure about that RedDanger? I'm nearly certain that thermal motion can cause electronic transitions. How else would hot gas emit radiation?
 
I'm assuming that by "hot gas" you're referring to a plasma, in which case I'm fairly certain that a large amount of thermal energy is supplied. For example, consider an ICP laser that reaches temperatures of up to 10000K. I can't think of another type of hot gas which would emit in the Vis region.

Another instance I was thinking of would be extremely hot metals, like Iron, which can turn white-hot (it's white because they're emitting Vis-region photons), or blackbody radiation. In any case, thermal energy can cause radiative emissions, but not necessarily in the Vis region of the EMR spectrum. At least, that's my understanding.
 
RedDanger said:
A collision can only result in a vibrational or rotational energy level transition. This is a transfer of kinetic energy. I would speculate (so don't quote me on this) that it would require extremely large amounts of thermal energy to cause an electronic transition as a result of kinetic energy transfer.
If that were true, then atoms, which only have electronic internal degrees of freedom, would never emit radiation when heated.

RedDanger said:
The molecule/particle must undergo nonradiative vibrational transitions in the form of collisions before its promoted electron can "relax" to its ground state.
It can undergo nonradiative transitions, but there is no reason why it must.
 

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