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.