2018 Census of Interstellar, Circumstellar, Extragalactic,
  Protoplanetary Disk, and Exoplanetary Molecules
  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
cm-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 this aggregate
data are presented and briefly discussed in context.
