0

I understand that visible light can (largely) go through greenhouse gases, but infrared radiation can get reflected back... why can visible light go through green-house gases?

Does it have to do with shorter wave-length of the visible light? i.e. are green house gases like a sieve that only allow shorter wavelengths in?

Qmechanic
  • 201,751
Hooman Bahreini
  • 127
  • Do you understand how the quantized energy levels of atoms allow only the absorption of photons whose energies are equal to the differences in energy levels? – G. Smith Nov 30 '19 at 05:44
  • The IR radiation isn't reflected. It is absorbed then re-emitted in a random direction i.e. 50% of the re-emitted radiation on average ends up headed back downwards. – John Rennie Nov 30 '19 at 06:13
  • @JohnRennie: thanks for your comment. So Co2 (or any other GH gas) absorbs infrared light, and then re-emits the infrared light in a random direction? Are you able to give a little more info about this please? Does Co2 enters an "unstable state" after absorbing the infrared light and that's why it re-emits it again? – Hooman Bahreini Nov 30 '19 at 06:20
  • @HoomanBahreini $\textrm{CO}_2$ has vibrational transitions at IR wavelengths so an IR photon is absorbed and excites the molecule to a higher energy state. The molecule then spontaneously decays back to the ground state and re-emits the photon in a random direction. – John Rennie Nov 30 '19 at 06:36
  • @JohnRennie: thanks a lot... So does it mean that visible light has too much energy? I assume excite means that an electron absorbs energy and jumps to higher level? So an infrared light has just the right amount of energy for this to happen, whereas visible light has too much energy so it cannot be absorbed? – Hooman Bahreini Nov 30 '19 at 06:43
  • @G.Smith: I have read your comment a couple of times over the past month and finally decided to recommend you to read this blog, which is about all Stack Exchange sites: Too many people experience Stack Overflow¹ as a hostile or elitist place, especially newer coders, women, etc... – Hooman Bahreini Dec 26 '19 at 06:28
  • @HoomanBahreini I am very sorry to learn that you construed my comment as hostile or elitist. It was certainly not intended to be either. I was trying to gauge what you already understood about how atoms interact with photons. Energy level differences in greenhouse gases are such that they easily interact with infrared photons but not with visible photons, using the formula $\Delta E=hf$. – G. Smith Dec 26 '19 at 11:47
  • This site gets questioners with many different levels of knowledge. When I ask someone on this site “Do you understand X?”, it is not a putdown but an attempt to understand how to provide an appropriate level of answer. – G. Smith Dec 26 '19 at 11:49
  • @G.Smith: if you say something like: "are you familiar with quantized energy levels of an atom?" then sure... but if you explain something and say "Do you understand this explanation?" then it's different. – Hooman Bahreini Dec 26 '19 at 20:19

0 Answers0