Infrared spectroscopy to solve interstellar puzzle
Thanks to sensitive infrared spectrographs of the Herschel mission and the Atacama Large Millimeter/submillimeter Array (ALMA), our understanding of interstellar infrared emission has improved greatly. The spectra at these wavelengths show a bedazzling variety of details that reflect the response of molecules to local conditions. Unravelling this chemical complexity requires a dedicated effort to characterise the infrared spectra of different chemical species in the laboratory. Within the context of the EU-funded project FISSA (The invisible made visible: Far-infrared spectroscopy in support of astrochemistry), researchers have developed an experimental set-up for studying analogues of interstellar dust grains. To achieve the conditions encountered in the interstellar medium, the researchers employed a thermal vacuum chamber, where pressure could reach values as low as 10^-8 Torr and temperatures ranged between 8 and 300 Kelvin. A commercial spectrometer was used along with one constructed in-house to cover both the mid- and far-infrared regions of the electromagnetic spectrum. Using a variety of experimental techniques – such as temperature programmed desorption and Monte Carlo simulations –the spectra of water and carbon dioxide in pure, mixed and layered ices of astrophysical relevance was characterised. The oxygenation of nitric oxide and the formation of larger nitrogen- and oxygen-bearing species were also studied under conditions close to those found in interstellar clouds. These studies have already led to much insight into the composition of interstellar dust grains. This includes many forms of water and organic molecules thought to be necessary for life. The results have been described in 14 publications in high-impact peer-reviewed journals. After the termination of the FISSA project, researchers anticipate extending this database to larger species and their physical properties.
Keywords
Infrared spectroscopy, interstellar dust grains, astrochemistry, thermal vacuum chamber, Monte Carlo simulations
