Infrared Spectra of Small Radicals for Exoplanetary Spectroscopy: OH, NH, CN and CH: The State of Current Knowledge

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 8; p. 3362
• Main Authors: Civiš, Svatopluk, Pastorek, Adam, Ferus, Martin, Yurchenko, Sergei N, Boudjema, Noor-Ines
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 11-04-2023; MDPI
• Subjects: Atmosphere; atmospheric chemistry; Discharge cells; Earth; Electrodes; Emission analysis; Emission spectra; Extrasolar planets; Fourier transforms; Free radicals; Glow discharges; Hydrocarbons; Infrared spectra; Infrared spectroscopy; Lightning; Line spectra; Planetary atmospheres; Planetary systems; Planets; Plasma; Prebiotics; radicals; Review; Saturn; short living radicals; Solar system; Space telescopes; Spectral resolution; spectroscopy; unstable species; Germany; unstable species; atmospheric chemistry; short living radicals; radicals; spectroscopy; infrared spectra
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28083362

In this study, we present a current state-of-the-art review of middle-to-near IR emission spectra of four simple astrophysically relevant molecular radicals-OH, NH, CN and CH. The spectra of these radicals were measured by means of time-resolved Fourier transform infrared spectroscopy in the 700-7500 cm
spectral range and with 0.07-0.02 cm
spectral resolution. The radicals were generated in a glow discharge of gaseous mixtures in a specially designed discharge cell. The spectra of short-lived radicals published here are of great importance, especially for the detailed knowledge and study of the composition of exoplanetary atmospheres in selected new planets. Today, with the help of the James Webb telescope and upcoming studies with the help of Plato and Ariel satellites, when the investigated spectral area is extended into the infrared spectral range, it means that detailed knowledge of the infrared spectra of not only stable molecules but also the spectra of short-lived radicals or ions, is indispensable. This paper follows a simple structure. Each radical is described in a separate chapter, starting with historical and actual theoretical background, continued by our experimental results and concluded by spectral line lists with assigned notation.