The Molecular Universe

Roughly two hundred molecules have been detected within the interstellar gas clouds that pervade our Galaxy, ranging from simple diatomic species to complex organic molecules.  These molecules exist within an unusual environment, exposed to ultraviolet radiation from hot stars, and to highly energetic charged particles, known as cosmic-rays, that fill the Galaxy with an energy density exceeding that of starlight. 

A careful analysis of the observed molecular composition of such gas clouds, performed with the use of sophisticated astrochemical models, can provide unique information about the astrophysical environments where molecules are present.  One recent example, to be discussed in this talk, is using the concentrations of multiple molecular ions  (ArH+, OH+, H2O+, and H3+) to make remote determinations of the density of cosmic-rays.

References:
(1) Gerin, Neufeld & Goicoechea, Ann. Rev. Astr. Ap. 2016, 54, 181
(2) Neufeld & Wolfire 2017, Astrophys. J. 845, 163