When astronomers see those fingerprints in a spectrum from Webb, they can then identify the molecule or family of molecules that created the absorption lines
Light from a star surrounded by a cloud of gas often shows absorption lines
produced when starlight of a specific energy is absorbed by atoms in the gas cloud.
First discovered in 1922, these absorption lines
(more than 400 of them) are seen any time astronomers look toward dust-reddened stars.
Based on the width of the absorption lines
and the intensity, the total pressure and the CO2 concentration in the package is determined.
While competitive laser-based instruments operate in the near-infrared range, the Delta Ray platform was designed to operate in the mid-infrared range because absorption lines
are about 8,000 times stronger than the NIR.
However, special measurement techniques have to be applied when weak absorption lines
Spectroscopic observations map the Mrk 509 warm absorber, study the mini-broad absorption line
quasar PG 1126-041, determine the source of reddening in low ionization BAL quasars, and probe quasar winds using narrow intrinsic absorption lines
Atomic and molecular absorption lines
are very stable under changing environmental conditions and are excellent references for this purpose.
Characteristic narrow absorption lines
, observed at 380 and 435 nm, are most likely from forbidden spin transitions in ferrous iron.
We have analyzed Fe 11 absorption lines
toward several of the reddened stars included in the FUSE survey of molecular hydrogen abundances in translucent clouds.
So, when patterns of dark absorption lines
with just those spacings show up in the spectra of quasars, astronomers conclude that an intervening gas cloud contains particular types of atoms.
Note that there are absorption lines
from various atmospheric gasses, but there are major transmission widows in the near-, mid-, and far-IR ranges.