As I mentioned the lack of time in post #1225....
I'd like to thank CraigD for a great job on the physics/quantum level stuff and thermodynamics part of answering Ceders question about a "chunk of CO2" in post #1230
My belief in Global Warming is getting shaky
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Originally Posted by CraigD
When a photon “strikes” (or, more precisely, interacts) with an electron in an atom of any kind of matter, it is absorbed by the electron if it’s possible for that electron to change its position in the atom (more precisely, its atomic orbital) so that its energy increases by exactly the energy of the absorbed photon. If this transition is possible for electrons in many atoms of a material (liquid, gas, or solid), that material is opaque (or possibly reflective) to photons of that energy. If it isn’t, the material is transparent to them.
Possible atomic orbital transitions depend mostly on the structure of the atom and its interaction with its neighboring atoms. In general, the more massive an atom, and the more bound it is into molecules with other atoms, the more possible transitions its electrons have.
The electrons in the atoms of CO2 and other greenhouse gas molecules are mostly transparent to visible light, and mostly opaque to infrared.
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Originally Posted by Re-quoting Cedars
How in the world does a vibrating CO2 chunk radiate HEAT?
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It’s important to understand that to “radiate heat” means to emit photons of infrared EMR.
Emission of photons is the reverse of absorption of them. |
One point I'd like to add (and please correct me if this is wrong or too fanciful):
The energy gained by absorbing an IR photon gets changed into kinetic energy (adding to the translational vibration) in the form of "speed" or velocity as well as other vibratory modes. Eventually, within seconds or minutes (depending on the concentration of possible collisions, uh....), ...eventually the molecule slows back down as it emits a photon ("re-emission").
So the kinetic energy is changed back into potential energy (photon) to be absorbed somewhere else.
Interestingly, several sources of kinetic energy can be summed within a molecule to create potential energy (an emission) of a higher energy level (quantum) than either kinetic contribution, by itself, would generate.
So, while usually the absorbed photon is "re-emitted" at the same or a lower energy level, with some of the kinetic energy bled off by collisions, entropy, whatever... sometimes a collision (or additional IR absorption) can provide the extra energy to boost a "re-emission" to a higher level than the original photon contributed.
So you have not only the actual process that CraigD described, but the added complexity of shifting levels of potential and kinetic energy--as quantum becomes classical and back again.
In summary GHG's are very good fluxes for that energy (heat) flowing around in the atmosphere--that is trying to make its way back out to space.
...and during that flux, a lot of the re-emissions are directed (randomly) back down toward the surface, or laterally towards other re-emitters ...away from deep space.
~
