Astrochemistry

Astrochemistry is the study of the abundance and reactions of molecules in the Universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word 'astrochemistry' may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form. Astrochemistry is the study of the abundance and reactions of molecules in the Universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word 'astrochemistry' may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form. As an offshoot of the disciplines of astronomy and chemistry, the history of astrochemistry is founded upon the shared history of the two fields. The development of advanced observational and experimental spectroscopy has allowed for the detection of an ever-increasing array of molecules within solar systems and the surrounding interstellar medium. In turn, the increasing number of chemicals discovered by advancements in spectroscopy and other technologies have increased the size and scale of the chemical space available for astrochemical study. Observations of solar spectra as performed by Athanasius Kircher (1646), Jan Marek Marci (1648), Robert Boyle (1664), and Francesco Maria Grimaldi (1665) all predated Newton's 1666 work which established the spectral nature of light and resulted in the first spectroscope. Spectroscopy was first used as an astronomical technique in 1802 with the experiments of William Hyde Wollaston, who built a spectrometer to observe the spectral lines present within solar radiation. These spectral lines were later quantified through the work of Joseph Von Fraunhofer. Spectroscopy was first used to distinguish between different materials after the release of Charles Wheatstone's 1835 report that the sparks given off by different metals have distinct emission spectra. This observation was later built upon by Léon Foucault, who demonstrated in 1849 that identical absorption and emission lines result from the same material at different temperatures. An equivalent statement was independently postulated by Anders Jonas Ångström in his 1853 work Optiska Undersökningar, where it was theorized that luminous gases emit rays of light at the same frequencies as light which they may absorb. This spectroscopic data began to take upon theoretical importance with Johann Balmer's observation that the spectral lines exhibited by samples of hydrogen followed a simple empirical relationship which came to be known as the Balmer Series. This series, a special case of the more general Rydberg Formula developed by Johannes Rydberg in 1888, was created to describe the spectral lines observed for Hydrogen. Rydberg's work expanded upon this formula by allowing for the calculation of spectral lines for multiple different chemical elements. The theoretical importance granted to these spectroscopic results was greatly expanded upon the development of quantum mechanics, as the theory allowed for these results to be compared to atomic and molecular emission spectra which had been calculated a priori. While radio astronomy was developed in the 1930s, it was not until 1937 that any substantial evidence arose for the conclusive identification of an interstellar molecule - up until this point, the only chemical species known to exist in interstellar space were atomic. These findings were confirmed in 1940, when McKellar et al. identified and attributed spectroscopic lines in an as-of-then unidentified radio observation to CH and CN molecules in interstellar space. In the thirty years afterwards, a small selection of other molecules were discovered in interstellar space: the most important being OH, discovered in 1963 and significant as a source of interstellar oxygen, and H2CO (Formaldehyde), discovered in 1969 and significant for being the first observed organic, polyatomic molecule in interstellar space The discovery of interstellar formaldehyde - and later, other molecules with potential biological significance such as water or carbon monoxide - is seen by some as strong supporting evidence for abiogenetic theories of life: specifically, theories which hold that the basic molecular components of life came from extraterrestrial sources. This has prompted a still ongoing search for interstellar molecules which are either of direct biological importance – such as interstellar glycine, discovered in 2009 – or which exhibit biologically relevant properties like Chirality – an example of which (propylene oxide) was discovered in 2016 - alongside more basic astrochemical research. One particularly important experimental tool in astrochemistry is spectroscopy through the use of telescopes to measure the absorption and emission of light from molecules and atoms in various environments. By comparing astronomical observations with laboratory measurements, astrochemists can infer the elemental abundances, chemical composition, and temperatures of stars and interstellar clouds. This is possible because ions, atoms, and molecules have characteristic spectra: that is, the absorption and emission of certain wavelengths (colors) of light, often not visible to the human eye. However, these measurements have limitations, with various types of radiation (radio, infrared, visible, ultraviolet etc.) able to detect only certain types of species, depending on the chemical properties of the molecules. Interstellar formaldehyde was the first organic molecule detected in the interstellar medium. Perhaps the most powerful technique for detection of individual chemical species is radio astronomy, which has resulted in the detection of over a hundred interstellar species, including radicals and ions, and organic (i.e. carbon-based) compounds, such as alcohols, acids, aldehydes, and ketones. One of the most abundant interstellar molecules, and among the easiest to detect with radio waves (due to its strong electric dipole moment), is CO (carbon monoxide). In fact, CO is such a common interstellar molecule that it is used to map out molecular regions. The radio observation of perhaps greatest human interest is the claim of interstellar glycine, the simplest amino acid, but with considerable accompanying controversy. One of the reasons why this detection was controversial is that although radio (and some other methods like rotational spectroscopy) are good for the identification of simple species with large dipole moments, they are less sensitive to more complex molecules, even something relatively small like amino acids.