How hot does Gaseous H2O need to be to emit IR Photons?

In summary, ten microns is the wavelength of IR light that is emitted by water vapor, liquid water, and clouds. The amount of IR light emitted corresponds to the temperature of the object. It is important to note that water vapor is fairly transparent to this wavelength, but liquid water absorbs it quite nicely. This band is one of the major sources of terrestrial IR for clouds, and the reason cloudy nighttime skies are "warmer" than clear ones.
  • #1
Michael Thornton
3
0
I've read that H2O has an absorption/emission band around to 10 micron range. What conditions are required for photons of this wavelength to be emitted by H20 gas? In particular, how hot would the gas have to be? What amount of pressure is required? Under everyday conditions (like steam possible to detect an appreciable amount of these photons?

Also, how would you determine this for any wavelength absorption/emission band?

Thanks for any and all responses!
 
Science news on Phys.org
  • #2
"Ten microns?" Room T.
 
  • #3
Bystander said:
"Ten microns?" Room T.

Ten micrometers
 
  • #4
Bystander knows what a micrometer is: he was answering your (main) question. To answer the follow-up question, it is a function of black body radiation (equations on its wiki page), with the peak frequency corresponding to the temperature:
BlackbodySpectrum_loglog_150dpi_en.png
 
  • #5
Ok, I guess I'll need to be more specific.

How much IR light would be radiated compared to a blackbody? I'm under the impression that water vapor is not a very good blackbody, so I'm trying to understand that idea a little better.
 
  • #6
I don't have specific answers, but I'd look into this in the context of weather forcasting: ir satellite photos of water vapor is one of our better tools for it.
 
  • #7
Actually, water vapor is fairly transparent to the ten micron wavelength band. That is why that band forms one of the humid atmosphere's IR "windows". On the other hand, liquid water absorbs it quite nicely. This band is one of the major sources of terrestrial IR for clouds, and the reason cloudy nighttime skies are "warmer" than clear ones. They produce "back" radiation to the Earth's surface that is absent under clear skies. This radiation, in turn, comes in large part from the warming caused by the absorption of the ten micron band. This band is the peak wavelength in the surface IR emissivity.
 

Related to How hot does Gaseous H2O need to be to emit IR Photons?

1. What is the relationship between temperature and the emission of IR photons in gaseous H2O?

The emission of IR photons in gaseous H2O is directly proportional to the temperature of the gas. This means that as the temperature increases, the emission of IR photons also increases.

2. Is there a specific temperature at which gaseous H2O emits IR photons?

Yes, there is a specific temperature at which gaseous H2O begins to emit IR photons. This temperature is known as the critical temperature and is approximately 374 degrees Celsius (647 degrees Fahrenheit).

3. Can gaseous H2O emit IR photons at lower temperatures?

Yes, gaseous H2O can emit IR photons at lower temperatures, but the amount of emission will be significantly lower compared to when it reaches the critical temperature. This is because the molecules of H2O are not as energized at lower temperatures, resulting in fewer IR photons being emitted.

4. How is the emission of IR photons from gaseous H2O affected by pressure?

The emission of IR photons from gaseous H2O is not significantly affected by pressure. However, at higher pressures, the critical temperature may shift, resulting in a different temperature at which gaseous H2O begins to emit IR photons.

5. Why is the emission of IR photons from gaseous H2O important?

The emission of IR photons from gaseous H2O is important because it plays a crucial role in the Earth's natural greenhouse effect. These photons trap heat in the Earth's atmosphere, helping to maintain a habitable temperature for living organisms. IR photon emission also helps to regulate the Earth's energy balance by transferring heat from the surface to the atmosphere.

Similar threads

I Stimulated Emission & Emitted photon direction
    • Optics
Replies
1
Views
1K
I How can a photon "stimulate emission" if it really does (Einstein coefficients)
    • Quantum Physics
Replies
11
Views
1K
I How does stimulated emission work in the process of light amplification?
    • Quantum Physics
Replies
6
Views
2K
Infrared Incandescence: How Hot Does It Need To Be?
    • Optics
Replies
2
Views
2K
How can infrared photons impart energy
    • Optics
Replies
11
Views
5K
Question about infrared radiation
    • Thermodynamics
Replies
8
Views
1K
How a solid body emits a lower frequency photon than absorbed
    • Electromagnetism
Replies
4
Views
1K
B Infrared Detectors & The 2nd Law of Thermodynamics
    • Thermodynamics
5
Replies
152
Views
5K
Laser Diode Principles: Stimulated Emission & Voltage
    • Atomic and Condensed Matter
Replies
2
Views
1K
How can we explain continuous absorption / emission?
    • Other Physics Topics
Replies
1
Views
1K

Hot Threads

Recent Insights

Back
Top