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The study and quantification of UV photon-induced desorption of frozen molecules furthers our understanding of the chemical evolution of cold interstellar regions. Nitric oxide (NO) is an important intermediate species in both gas-phase and solid-phase chemical networks. In this work, we present quantitative measurements of the photodesorption of a pure NO ice. We used the tunable monochromatic synchrotron light of the DESIRS beamline of the SOLEIL facility near Paris to irradiate NO ices in the 6–13.6 eV range and measured desorption by quadrupole mass spectrometry. We find that NO photodesorption is very efficient, its yield being around 10−2 molecule per incident photon for UV fields relevant to the diffuse and dense interstellar medium. We discuss the extrapolation of our results to an astrophysical context and we compare photodesorption of NO to previously studied molecules. [ABSTRACT FROM AUTHOR]

Context. Methane is among the main components of the ice mantles of interstellar dust grains, where it is at the start of a rich solid-phase chemical network. Quantification of the photon-induced desorption yield of these frozen molecules and understanding of the underlying processes is necessary to accurately model the observations and the chemical evolution of various regions of the interstellar medium. Aims. This study aims at experimentally determining absolute photodesorption yields for the CH4 molecule as a function of photon energy. The influence of the ice composition is also investigated. By studying the methane desorption from layered CH4:CO ice, indirect desorption processes triggered by the excitation of the CO molecules are monitored and quantified. Methods. Tunable monochromatic vacuum ultraviolet light (VUV) light from the DESIRS beamline of the SOLEIL synchrotron is used in the 7-13.6 eV (177-91 nm) range to irradiate pure CH4 or layers of CH4 deposited on top of CO ice samples. The release of species in the gas phase is monitored by quadrupole mass spectrometry, and absolute photodesorption yields of intact CH4 are deduced. Results. CH4 photodesorbs for photon energies higher than ~9.1 eV (~136 nm). The photodesorption spectrum follows the absorption spectrum of CH4, which confirms a desorption mechanism mediated by electronic transitions in the ice. When it is deposited on top of CO, CH4 desorbs between 8 and 9 eV with a pattern characteristic of CO absorption, indicating desorption induced by energy transfer from CO molecules. Conclusions. The photodesorption of CH4 from pure ice in various interstellar environments is around 2.0 ± 1.0 × 10-3 molecules per incident photon. Results on CO-induced indirect desorption of CH4 provide useful insights for the generalization of this process to other molecules co-existing with CO in ice mantles. [ABSTRACT FROM AUTHOR]

Spectroscopic investigations of PAHs have been conducted for many years, commencing with solid and solution studies and more recently including gas phase characterisation of a broad range of different species. Through the development of new, efficient methods of production and more sensitive spectroscopic techniques, fresh data are becoming available for not only neutral species, but also for radicals, ions and clusters. [ABSTRACT FROM PUBLISHER]

Context. Carbonaceous cosmic dust is observed through infrared spectroscopy either in absorption or in emission. The details of the spectral features are believed to shed some light on its structure and finally enable the study of its life cycle. Aims. The goal is to combine several analytical tools in order to decipher the intimate nanostructure of some soot samples. Such materials provide interesting laboratory analogues of cosmic dust. In particular, spectroscopic and structural characteristics that help to describe the polyaromatic units embedded into the soot, including their size, morphology, and organisation are explored. Methods. Laboratory analogues of the carbonaceous interstellar and circumstellar dust were produced in fuel-rich low-pressure, premixed and flat flames. The soot particles were investigated by infrared absorption spectroscopy in the 2-15 μm spectral region. Raman spectroscopic measurements and high-resolution transmission electron microscopy were performed, which offered complementary information to better delineate the intimate structure of the analogues. Results. These laboratory analogues appeared to be mainly composed of sp2 carbon, with a low sp3 carbon content. A cross relation between the positions of the aromatic C=C bands at about 6.2 micron and the band at about 8 micron is shown to trace differences in shapes and structures of the polyaromatic units in the soot. Such effects are due to the defects of the polyaromatic structures in the form of non-hexagonal rings and/or aliphatic bridges. The role of these defects is thus observed through the 6.2 and 7.7 μm aromatic infrared band positions, and a distinction between carriers composed of curved aromatic sheets and more planar ones can be inferred. Based on these nanostructural differences, a scenario of nanograin growth and evolution is proposed. [ABSTRACT FROM AUTHOR]

Context. Carbonaceous cosmic dust is observed through infrared spectroscopy either in absorption or in emission. The details of the spectral features are believed to shed some light on its structure and finally enable the study of its life cycle. Aims. The goal is to combine several analytical tools in order to decipher the intimate nanostructure of some soot samples. Such materials provide interesting laboratory analogues of cosmic dust. In particular, spectroscopic and structural characteristics that help to describe the polyaromatic units embedded into the soot, including their size, morphology, and organisation are explored. Methods. Laboratory analogues of the carbonaceous interstellar and circumstellar dust were produced in fuel-rich low-pressure, premixed and flat flames. The soot particles were investigated by infrared absorption spectroscopy in the 2-15 μm spectral region. Raman spectroscopic measurements and high-resolution transmission electron microscopy were performed, which offered complementary information to better delineate the intimate structure of the analogues. Results. These laboratory analogues appeared to be mainly composed of sp2 carbon, with a low sp3 carbon content. A cross relation between the positions of the aromatic C=C bands at about 6.2 micron and the band at about 8 micron is shown to trace differences in shapes and structures of the polyaromatic units in the soot. Such effects are due to the defects of the polyaromatic structures in the form of non-hexagonal rings and/or aliphatic bridges. The role of these defects is thus observed through the 6.2 and 7.7 μm aromatic infrared band positions, and a distinction between carriers composed of curved aromatic sheets and more planar ones can be inferred. Based on these nanostructural differences, a scenario of nanograin growth and evolution is proposed. [ABSTRACT FROM AUTHOR]

Carbonaceous cosmic dust is observed through infrared spectroscopy either in absorption or in emission and the details of the spectral features are believed to shed some light on its structure and finally enable the study of its life cycle. Other spectral domains also contain some information, as does the UV bump at 217 nm. In order to progress on the understanding of these spectral features, many laboratory works are devoted to the production and characterization of laboratory analogues. Generally several analytical tools are used in combination to better analyse the intimate structure of the analogues and the influence of the nanostructuration on the spectral properties. In this proceeding We will focus on the elaboration of new spectral parameters that enables the nanostructuration of the carriers of the AIBs to be traced. [ABSTRACT FROM PUBLISHER]