Astronomy Molecular identification

One of the oldest problems in molecular astronomy concerns identification of the molecules responsible for diffuse interstellar bands (DIBs). Since their first observation in 1922 some 127 bands have been detected all over the electromagnetic spectrum, shown schematically in Figure 3.19, but the origins of the transitions, the so-called carriers of DIBs, have not been determined. 

Swings and Rosenfeld, 1937 McKellar, 1940). The discovery in 1963 of the XI8 cm radio spectrum of OH by Weinreb et al. was the first identification of an interstellar molecule by radio astronomy. Thus, up until 1968, only four interstellar molecules were known to exist, leading to the generally accepted conclusion that simple free radicals were the main interstellar molecular constituents in a highly dilute gas (< 1 particle cm-3), subject to ionizing ultraviolet radiation. 

If a sufficient number of resonances with laser lines can be found, the rotational constant, the fine structure parameters, and the magnetic moments can be determined very accurately. The identification of the spectra and the assignment of the lines are often possible even if the molecular constants are not known beforehand [144]. Most radicals observed in interstellar space by radio astronomy [141a] have been found and measured in the laboratory with LMR spectroscopy [141b]. 

The fact that the CPMD was a milestone step forward in realistic simulations of materials, at various thermodynamics conditions, can be easily seen by the number of publications in first principles molecular dynamics (FPMD) before and after 1985, i.e. after the original CPMD publication [21]. Indeed, the original Car-Parrinello publication has more than 6500 citations in 2014 (source ISI Web of Science), and, to acknowledge the importance of the method, the international PACS (Physics and Astronomy Classification Scheme) introduced in 1996 a new identification number, 71.15. Pd, to classify Car-Parrinello related publications. Since then, the method has been applied to a wide variety of materials, ranging from solids, to liquids and to biological systems [33]. 

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