Science Forums 2

[CraigD]

Originally Posted by Cedars

So why cant anyone tell me what the IR wave converts to when its heats up the Co2 bubble?

First, it’s important to understand that electromagnetic radiation, isn’t purely a wave phenomena, but both wave like and particle like. For this explanation, where wave like effects such as refraction and interference aren’t important, but absorption is, it’s most convenient to stick with a particle description.

EMR particles, or quanta, are called photons. Visible light is composed of photons with individual energies between about 3.1 and 1.8 eV, infrared radiation with energies between about 1.8 eV and 0.001 eV. Photons above about 3.1 eV constitute ultraviolet, x-ray, and gamma EMR.

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.

Originally Posted by Cedars

How in the world does a vibrating CO2 chunk radiate HEAT?

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. If it is possible for an electron to transition to an orbital with less energy than its current one, it will, emitting a photon with the energy of the difference between the old and new orbital.

What occurs between the emission and absorption of photons by the electrons in the atoms of materials accounts for the optical differences between materials. A material of atoms strongly bound in a solid matrix usually almost immediately reemits a photon of the same energy it absorbed, so materials like solid metals tend to be reflective, and be heated relatively little by EMR. A material of loosely bound atoms such as a gas usually transfers the momentum of the absorbed photons to itself and its neighbors, emitting photons in a fairly random manner. Materials like the solids and liquids on the Earth’s surface behave this way, absorbing visible and infrared radiation and emitting most of it as infrared. Greenhouse gases in the atmosphere (or solids such as glass in an actual greenhouse) are transparent to visible light, but absorb and reemit infrared. This emitted infrared EMR is many times reabsorbed by other atmosphere and surface atoms, and emitted into space.

Note that the infrared band of EMR spans a much greater energy range, about 11 doublings (or “octaves”), than visible light, which spans about 1 octave. Although infrared photons can, therefore, be much more different in energy than photons of visible light, they’re effectively nearly identical, in that they all can be absorbed by the same materials.

It’s possible to make atoms absorb infrared and emit visible EMR – this is what happens when a heated material visibly glows. These materials continue to emit mostly in the infrared, however, so there’s not practical way to “trick” common materials into producing a “reverse greenhouse effect”, although an exotic, as yet not realized device such a s “heat pumped optical laser” is, to the best of my knowledge, possible in principle.