# What is the absorption spectrum of liquid nitrogen?

I know that even pure water absorbs some visible light enough to be noticeable over short distances. According to the file File:Absorption spectrum of liquid water.png, the the wavelength of visible light with the lowest absorptivity is 500 nm at about 0.02 $$m^{-1}$$ and the wavelength of visible light with the highest absorptivity is probably the red end of the spectrum at 700 nm at about 1 $$m^{-1}$$.

As described later, I suspect that liquid nitrogen is much less absorbent of visible light. I'm imagining up a much colder planet than Earth where we have liquid nitrogen based life. If I was one of those life forms, I would have thought of liquid nitrogen the same way as I think of water, yet when that liquid is pure, it would probably be extremely transparent to visible light. It feels so wierd how transparent something I think of the same way as water would be.

My question is

What is the absorption spectrum of liquid nitrogen?

I once saw a YouTube video with liquid nitrogen and I believe that water has a high enough absorptivity of red light that even with a low depth of approximately a decimeter, I could tell that it was clearer than water. I suspect liquid nitrogen is extremely transparent in visible light. The fine structure constant is small at about $$\frac{1}{137}$$ and a photon released by an electron jumping from the second energy level to the first energy level in a hydrogen atom is in the visible region. That's probably part of the reason for the low absorptivity of liquid nitrogen. Also a nitrogen molecule hybridizes in such a way that the 1s and 2s orbitals don't hybridize and each p orbital of one atom hybridizes with a p orbital of the other atom to create a bonding orbital and an antibonding orbital and all the bonding orbitals are filled but none of antibonding orbitals are. That also appears to give no way for a photon of visible light to be absorbed through the jumping of an electron to a higher energy level.

From reading the Vibrational spectrum section of the Wikipedia article Electromagnetic absorption by water, I think some of the absorption of water comes from vibrational transitions. A water molecule has 3 degrees of freedom of vibration and according to what somebody once told me, the hydrogen atoms have a really low mass. The absorption by vibrational transition probably partly extends to visible red light for that reason. A nitrogen molecule on the other hand is diatomic so it has only 1 degree of freedom of vibration. Also since a nitrogen atom is about 14 times as massive as a hydrogen atom, the absorption by vibrational transition is probably in electromagnetic radiation of lower wavelength.

• Lots of info on the far infrared, harder to find for visible. Not clear why you have this tagged 'particle-physics' though (unless you want to talk about Cherenkov counters). Nov 22 '19 at 18:42
• @JonCuster I think that other users have expert knowledge that I don't have making it hard for me to figure out how to tag questions properly. I added a tag because I have to but I prefer an answer that totally ignores the tag. For questions asked by somebody like me, probably just the body of the text and not the tag gives a lot of information about what the question asker is looking for. Nov 22 '19 at 18:53
• I'm wondering whether if this question got moved to chemistry Stack Exchance, there would be a higher chance that one of its users would be able to answer this question. Nov 27 '19 at 23:00
• I didn't think properly. I should have asked this on Chemistry Stack Exchange. It's in a course called "Physical Inorganic Chemistry" that I learned how the molecules from hydrogen to neon really hybridize. I know Physics Stack Exchange can answer some questions about quantum mechanics and hybridization is explained by quantum mechanics. Would it be possible for somebody to move it to Chemistry Stack Exchange. Dec 14 '19 at 2:23