# Why N$_2$ is a non-absorbing species in the spectrum of the Earth?

The transmission spectrum of the Earth atmosphere is like that (Kaltenegger & Traub 2009):

As you can see, you can find many absorption lines related to some components of Earth's atmosphere: H$$_2$$O, O$$_2$$, CO$$_2$$, O$$_3$$, CH$$_4$$... But the nitrogen, N$$_2$$, is not detected anywhere in the spectrum. Why N$$_2$$ is not detected, but O$$_2$$, for example, is?

• This might be usefully asked on Chemistry stack. – James K Jun 30 '20 at 22:35
• conversely, Chemistry SE can be invited here, as can Earth Science SE – uhoh Jun 30 '20 at 23:36
• As the answer points out, the first thing to do is to look up the absorption wavelengths (or spectral map) for N2 . – Carl Witthoft Jul 1 '20 at 12:55