Which easily observed molecular species is used as a tracer for the fundamental but difficult to observe H₂ molecules in giant molecular clouds?

Question

Quizplus · Accepted Answer

Carbon monoxide is often used as a tracer for H₂ molecules in giant molecular clouds as they have similar physical properties and are found together. CO can be easily observed due to its strong dipole moment which emits radiation at a certain frequency that can be detected by telescopes. Moreover, CO is much more abundant and easier to detect compared to H₂ molecules. The other molecules listed (OH, H₂O, CO₂) are not commonly used as tracers for H₂ molecules.

Which Easily Observed Molecular Species Is Used as a Tracer