Electromagnetic Absorption Frequency

[TESL@]

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.

 

[UltrafastPED]

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

 

[TESL@]

Thanks UltrafastPED.

 

[TESL@]

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?

 

[UltrafastPED]

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.

 

[TESL@]

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.

 

[TESL@]

Is there anyone to verify?

 

[UltrafastPED]

The Hyperphysics site explains how to use this formula:
http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/vibrot.html#c2

It's a specialized approximation for vibrational modes - and treats the diatomic molecule as a quantized spring.