Atomic and molecular astronomy

The study of spectroscopy has provided all of the information required to make a positive identification of molecules in space. More interestingly, once the spectrum of a molecule or atom is understood accurately, the interaction of the molecule with its surroundings can be understood as well. Atoms and molecules, wherever they are, can report on their local conditions and be used as probes. We shall see many of these examples where knowledge of molecular properties provides insight into astrochemistry. For example, the understanding developed below will take us from the transition wavelength of Ha to the radius of Jupiter. 

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W.C. Martin, Sources of Atomic Spectroscopy Data for Astrophysics , in PL. Smith and W. L. Wiese (eds.), Atomic and Molecular Data for Space Astronomy Needs, Analysis and Availability, Springer, Berlin, 1992. 

This book is about life, mostly about the molecules of life. Molecules are the focus of the science of chemistry, just as animals are the focus for zoology, plants are the focus for botany, and outer space is the focus for astronomy. A bit more broadly, chemistry is the science of the composition, structure, properties, and reactions of matter, especially of atomic and molecular systems. Let s talk a bit about chemistry, the molecular science. 

Under the editorship of A. Eucken, the sixth edition of Landolt-Bomsteins Zahlenwerte und Fimktionen aus Physik, Ghemie, Astronomie, Geophysik und Technik began appearing in 1950. Volumes I and II together form the new edition of the old (1936) set Volume I deals with atomic and molecular physics Volume II, with macrophysics and chemistry. (Volume I, in five parts, was published by 1955 three parts of Volume II were available by 1960.) Publication of Volumes III and IV proceeds more slowly. 

In many ways, the present situation resembles the situation of optical astronomy in the beginning of the last century Back then, the available observational data mainly consisted in images, starcounts, variability s, and colors. Astrophysics was born in 1859 when G. Kirchhof and R. Bunsen developed the spectral analysis and explained the Frauenhofer-lines in the spectrum of the sun. The exploration of atomic and molecular lines has since turned out to be the most powerful tool for the study of the physical conditions in celestial sources. 

PL. Smith, W.L. Wiese Atomic and Molecular Data for Space Astronomy (Springer, Berlin 1992)... 

One task awaiting molecular astronomy is to find the missing links that separate 11-atom molecules from PAHs and fullerenes with 20 to 60 atoms, whilst a whole world lies between the most evolved molecules and a simple dust grain which contains, at the lowest estimate, 1 billion atoms. 

Molecular astronomy of carbon molecules is very rich. Of about 120 known interstellar molecules more than three-quarters contain carbon atoms diatomic molecules include CO, CN, C2, CH, CH+, CN+, and CO+ polyatomic include CH2, CH4, C2H2j CH OH, CH3CH2OH, H2CO and HNC large complex unsaturated radicals and polycyclic aromatic hydrocarbons are also detected. These all play a role in the thermochemistry of interstellar clouds. The 2.6-millimeter line of CO diagnoses density and temperature in molecular clouds, as do other molecules. 

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