Electromagnetic Absorption Frequency

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Discussion Overview

The discussion revolves around the absorption frequencies of nitrogen molecules in the air, particularly in relation to their molecular structure and how this affects their interaction with electromagnetic waves. Participants explore methods for calculating absorption wavelengths and share resources for further understanding.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the specific wavelengths that nitrogen molecules can absorb, noting the absorption characteristics of water molecules as a point of reference.
  • Another participant suggests searching for the "Molecular nitrogen absorption spectrum" and provides links to resources, including a paper discussing the complexity of nitrogen's absorption spectrum.
  • A participant expresses confusion regarding the units obtained from their calculations, questioning the validity of their results.
  • Another participant advises reviewing a lecture on ideal diatomic gases to understand the derivation of the equation used and its limitations.
  • A participant calculates a wavelength of vibration for nitrogen and expresses surprise at the result, which they expected to be in the ultraviolet range.
  • One participant shares a link to Hyperphysics, indicating that the formula discussed is a specialized approximation for vibrational modes of diatomic molecules.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints regarding the absorption characteristics of nitrogen and the validity of the calculations presented. Participants express uncertainty about the equations and results, and no consensus is reached on the correct approach or interpretation.

Contextual Notes

Participants highlight potential limitations in the equations used, including concerns about unit consistency and the applicability of certain models to nitrogen's absorption spectrum.

TESL@
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Hi, I have just registered to ask something that I can't find the answer anywhere.

As you know, microwaves are absorbed by water molecules because of its shape and angles etc. I wonder which wavelength can be absorbed by nitrogen molecules in the air or at least need to learn a method to calculate.

Thank you.
 
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Search for "Molecular nitrogen absorption spectrum".

You will find lots of details at NIST:
http://webbook.nist.gov/cgi/cbook.cgi?ID=C7727379&Mask=1000

You can forget calculations unless this is your research specialty - but see this paper:
"On the complexity of the absorption spectrum of molecular nitrogen"
http://www.nat.vu.nl/en/sec/atom/Publications/pdf/Vieitez-08-ML.pdf

However, this lecture has a very simple formula on page 8; of course it only gives one frequency, so it is based on a very simple model: http://www.geo.mtu.edu/~scarn/teaching/GE4250/absorption_lecture.pdf

But the lecture is also worthwhile - it provides a great deal of information, but not much on N2.

Also see "The spectrum of molecular nitrogen": (behind paywall)
http://scitation.aip.org/content/aip/journal/jpcrd/6/1/10.1063/1.555546
 
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Thanks UltrafastPED.
 
Absorbtion_Frequency.png


When I calculate, I get a result of wavenumber in terms of s/(m√m) whereas it actually in 1/m. How can it be correct?
 
Last edited:
I don't know where that equation came from, and I don't trust it.

Search for Chapter 6 Ideal Diatomic Gas;
This lecture goes through a typical derivation process ... if you read it carefully you may find out how the above formula was generated, and its limitations.
 
Ok, from the equation v=(1/2∏)*√(k/u), and k=22,6*105dyn/cm for N2, the wavelength of vibration has been found 13517,28566 nm. This is way too long, I expected ultraviolet bands.

By the way, I took the previous equation from http://www.geo.mtu.edu/~scarn/teaching/GE4250/absorption_lecture.pdf pg:8.
 
Last edited:
Is there anyone to verify?
 

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