2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

Abstract

To date, 204 individual molecular species, comprised of 16 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to seventy, and have been detected across the electromagnetic spectrum from cmwavelengths 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 this aggregate data are presented and briefly discussed in context.

Diatomic Rovibronic Transitions as Potential Probes for Proton-to-Electron Mass Ratio Across Cosmological Time

“…Small (N<8) polyatomic molecules that have been observed in extragalactic environments [70]. H 2 CS is a tentative detection.…”

“…The subset of molecules that have been observed in space is tiny compared to all of the molecules on Earth. Table 2 lists all of the diatomics which have been observed in the interstellar medium, circumstellar shells or extragalactically [70], together with some other information which we will discuss further in section 4.2 and section 5. Just 19 diatomic molecules have been observed extragalactically (shown in bold in Table 2).…”

“…have been detected within the interstellar medium, [70] Table 3 shows the 42 that have been observed extragalactically.…”

“…Lambda doubling transitions have been observed at medium redshift for NO and SO + [43] as well as OH [52]. Galactic observations of lambda-doubling transitions of HCl + [70] suggest possible future interest. CN, AlO, CP, C 2 , and SiN have relatively low (<10000 cm −1 ) Π electronically excited states, which may be of interest for lambda-doubling.…”

The Submillimeter Rotational Spectrum of Ethylene Glycol up to 890 GHz and Application to ALMA Band 10 Spectral Line Data of NGC 6334I

“…Of the more than 200 molecules detected in the interstellar medium (ISM) to date, more than 80% were discovered through observations of their pure rotational transitions. 1 With few exceptions, [2][3][4] the detection and characterization of molecules in the ISM is preceded by high-resolution spectroscopic investigations in the laboratory. Depending on the molecular structure, many thousands of line frequencies may be measured and fit using common software packages 5,6 to a Hamiltonian, 7 providing a set of rotational constants (A, B, C) as well as higher-order terms that account for the effects of centrifugal distortion, internal motion, fine and hyperfine coupling, etc.…”