2021 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

Abstract

To date, 241 individual molecular species, composed of 19 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to 70 and have been detected across the electromagnetic spectrum from centimeter wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of these aggregate data are presented and briefly discussed in context.

HyGAL: Characterizing the Galactic Interstellar Medium with Observations of Hydrides and Other Small Molecules. I. Survey Description and a First Look Toward W3(OH), W3 IRS5, and NGC 7538 IRS1

“…Being poorly shielded against photodissociating interstellar radiation fields, the low-density (n H ∼ 10 2 -10 3 cm −3 ) gas comprising diffuse clouds was originally predicted to be devoid of molecules (Eddington 1926). However, observations at ultraviolet, visible, and radio wavelengths have revealed an astounding inventory of molecules (Goss 1968;Whiteoak & Gardner 1970;Lucas & Liszt 1996;Snow & McCall 2006;McGuire 2022). The surprisingly rich chemistry present in diffuse clouds can be attributed to exothermic reactions driven by cosmic-ray ionization and large fluctuations in the thermal pressure of the media.…”

Semiempirical Potential in Kinetics Calculations on the HC3N + CN Reaction

“…Since the detection of the first molecular species, namely, the CH [ 1 ] and CN [ 2 , 3 ] molecules in dark clouds as well as in the Orion nebula and in the W51 region, huge efforts have been performed in order to unveil molecular complexity and understand the chemistry of the interstellar medium (ISM). Currently, more than 241 species have been detected in different regions of space [ 4 ], starting from simple molecules, up to more complex species with a strong prebiotic potential, such as formamide [ 5 ]. The understanding of the chemical processes which are considered the responsible for the formation and destruction of interstellar molecules in harsh conditions, where the temperature can go down to 10 K and the particle density can be as low as 10 particles cm [ 6 ], is a challenge for modern astrochemists.…”

Infrared free-electron laser irradiation of carbon dioxide ice

“…To date, more than 240 different species have been identified in space in the gas phase [1]. Since gas-phase reaction rates are often found to be too low to account for the observed abundances of species in space, the icy mantles of interstellar dust grains are believed to give rise to a rich prebiotic chemistry, which feeds complex organic molecules (COMs) to star-forming regions and ultimately to planetary systems [2,3,4].…”