My understanding is that when a $\rm CO_2$ molecule absorbs a photon of heat in the atmosphere after some time it simply re-emits that photon in a random direction. If that photon makes it back to its source (the Earth) this is the major mechanism of global warming. Sabine Hossenfelder said in a YouTube video https://youtube.com/watch?v=oqu5DjzOBF8&feature=share explaining global warming says that the vibrational energy of the excited $\rm CO_2$ molecule is distributed to other molecules in the atmosphere when they collide (6min 10sec-6min-30sec) and this warms the atmosphere. Is the vibrational excited energy of the $\rm CO_2$ molecule transferred to the translational energy of its colliding partner during a collision?
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$\begingroup$ What is the vibrational energy level in eV, vs. local $kT$? $\endgroup$– JEBCommented Feb 12, 2023 at 22:06
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$\begingroup$ @JEB The 4 modes are within ~3-12 times kT. $\endgroup$– Michael D MaysCommented Feb 12, 2023 at 23:10
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2 Answers
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when a CO2 molecule absorbs a phonon of heat ...
Why phonon here? That's not normally associated with energy exchange in a gas. The molecule can gain energy by absorbing IR energy or by interactions with other molecules (collisions).
it simply re-emits that phonon in a random direction.
It is possible for an excited CO2 molecule to emit IR randomly, yes.
Is the vibrational excited energy of the CO2 molecule transferred to the translational energy of its colliding partner during a collision?
That's possible, yes. For a collection in thermal equilibrium, energy is moving between kinetic and vibrational modes. Energy can be dumped into any single mode and it will equilibrate into others via collisions.
See also: Gases: Interplay of vib, rot and translational energy
answered Feb 13, 2023 at 7:06
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The primary reason of the (both natural and human-triggered) greenhouse effect (GE) of greenhouse gases (GGs) is decreased Earth emission to the space for IR wavelengths, that are absorbed by GGs. This is surprisingly caused by their emision, not absorption.
IR radiation at these wavelengths, which is going into space, is emitted mostly by cold (down to 220 K), low radiating atmosphere and not by warm, high radiating Earth surface.
Due outgoing energy deficit with raising concentration of GGs, the mean (spatially and temporally) Earth surface temperature slowly raises up. It leads to emitting more IR going directly to space at wavelengths not absorbed by GGs, what converges to balancing the mentioned emission deficit.
How this is done -- re-emission of IR in random direction, de-excitation by collisions increasing atmosphere temperature, forced/thermal convection heat transfer -- are secondary local details.
