Photodesorption of Acetonitrile CH3CN in UV-irradiated Regions of the Interstellar Medium: Experimental Evidence

Abstract Pure acetonitrile (CH3CN) and mixed CO:CH3CN and H2O:CH3CN ices have been irradiated at 15 K with vacuum ultraviolet (VUV) photons in the 7–13.6 eV range using synchrotron radiation. VUV photodesorption yields of CH3CN and of photoproducts have been derived as a function of the incident photon energy. The coadsorption of CH3CN with CO and H2O molecules, which are expected to be among the main constituents of interstellar ices, is found to have no significant influence on the VUV photodesorption spectra of CH3CN, CHCN•, HCN, CN•, and CH3•. Contrary to what has generally been evidenced for most of the condensed molecules, these findings point toward a desorption process for which the CH3CN molecule that absorbs the VUV photon is the one desorbing. It can be ejected in the gas phase as intact CH3CN or in the form of its photodissociation fragments. Astrophysical VUV photodesorption yields, applicable to different locations, are derived and can be incorporated into astrochemical modeling. They vary from 0.67(± 0.33) × 10−5 to 2.0(± 1.0) × 10−5 molecule photon−1 for CH3CN depending on the region considered, which is high compared to other organic molecules such as methanol. These results could explain the multiple detections of gas-phase CH3CN in different regions of the interstellar medium and are well correlated to astrophysical observations of the Horsehead nebula and of protoplanetary disks (such as TW Hya and HD 163296).

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The Effect of Positive End-Expiratory Pressure on Lung Micromechanics Assessed by Synchrotron Radiation Computed Tomography in an Animal Model of ARDS

Journal of Clinical Medicine ◽

10.3390/jcm8081117 ◽

2019 ◽

Vol 8 (8) ◽

pp. 1117 ◽

Cited By ~ 5

Author(s):

Gaetano Scaramuzzo ◽

Ludovic Broche ◽

Mariangela Pellegrini ◽

Liisa Porra ◽

Savino Derosa ◽

...

Keyword(s):

Computed Tomography ◽

Animal Model ◽

Acute Respiratory Distress Syndrome ◽

Synchrotron Radiation ◽

Gas Phase ◽

Phase Contrast ◽

Distress Syndrome ◽

Regions Of Interest ◽

Positive End Expiratory Pressure ◽

The One

Modern ventilatory strategies are based on the assumption that lung terminal airspaces act as isotropic balloons that progressively accommodate gas. Phase contrast synchrotron radiation computed tomography (PCSRCT) has recently challenged this concept, showing that in healthy lungs, deflation mechanisms are based on the sequential de-recruitment of airspaces. Using PCSRCT scans in an animal model of acute respiratory distress syndrome (ARDS), this study examined whether the numerosity (ASnum) and dimension (ASdim) of lung airspaces change during a deflation maneuver at decreasing levels of positive end-expiratory pressure (PEEP) at 12, 9, 6, 3, and 0 cmH2O. Deflation was associated with significant reduction of ASdim both in the whole lung section (passing from from 13.1 ± 2.0 at PEEP 12 to 7.6 ± 4.2 voxels at PEEP 0) and in single concentric regions of interest (ROIs). However, the regression between applied PEEP and ASnum was significant in the whole slice (ranging from 188 ± 52 at PEEP 12 to 146.4 ± 96.7 at PEEP 0) but not in the single ROIs. This mechanism of deflation in which reduction of ASdim is predominant, differs from the one observed in healthy conditions, suggesting that the peculiar alveolar micromechanics of ARDS might play a role in the deflation process.

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Vacuum Ultraviolet Photoionization Study of Gas Phase Vitamins A and B1 Using Aerosol Thermodesorption and Synchrotron Radiation

The Journal of Physical Chemistry A ◽

10.1021/jp507050y ◽

2014 ◽

Vol 118 (47) ◽

pp. 11185-11192 ◽

Cited By ~ 7

Author(s):

Héloïse Dossmann ◽

Adrián Schwarzenberg ◽

Denis Lesage ◽

Marie Pérot-Taillandier ◽

Carlos Afonso ◽

...

Keyword(s):

Synchrotron Radiation ◽

Gas Phase ◽

Vacuum Ultraviolet

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The formation of urea in space

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731610 ◽

2018 ◽

Vol 610 ◽

pp. A26 ◽

Cited By ~ 7

Author(s):

Flavio Siro Brigiano ◽

Yannick Jeanvoine ◽

Antonio Largo ◽

Riccardo Spezia

Keyword(s):

Activation Energy ◽

Interstellar Medium ◽

Gas Phase ◽

Organic Molecules ◽

Peptide Bond ◽

Biological Molecules ◽

Gas Phase Reactions ◽

Molecule Reaction ◽

Quantum Chemistry Calculations ◽

Highly Correlated

Context. Many organic molecules have been observed in the interstellar medium thanks to advances in radioastronomy, and very recently the presence of urea was also suggested. While those molecules were observed, it is not clear what the mechanisms responsible to their formation are. In fact, if gas-phase reactions are responsible, they should occur through barrierless mechanisms (or with very low barriers). In the past, mechanisms for the formation of different organic molecules were studied, providing only in a few cases energetic conditions favorable to a synthesis at very low temperature. A particularly intriguing class of such molecules are those containing one N–C–O peptide bond, which could be a building block for the formation of biological molecules. Urea is a particular case because two nitrogen atoms are linked to the C–O moiety. Thus, motivated also by the recent tentative observation of urea, we have considered the synthetic pathways responsible to its formation. Aims. We have studied the possibility of forming urea in the gas phase via different kinds of bi-molecular reactions: ion-molecule, neutral, and radical. In particular we have focused on the activation energy of these reactions in order to find possible reactants that could be responsible for to barrierless (or very low energy) pathways. Methods. We have used very accurate, highly correlated quantum chemistry calculations to locate and characterize the reaction pathways in terms of minima and transition states connecting reactants to products. Results. Most of the reactions considered have an activation energy that is too high; but the ion-molecule reaction between NH2OHNH2OH2+ and formamide is not too high. These reactants could be responsible not only for the formation of urea but also of isocyanic acid, which is an organic molecule also observed in the interstellar medium.

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Carbon-grain sublimation: a new top-down component to protostellar chemistry

10.5194/epsc2020-960 ◽

2020 ◽

Author(s):

Merel van 't Hoff ◽

Edwin Bergin ◽

Jes Jorgensen ◽

Geoffrey Blake

Keyword(s):

Gas Phase ◽

Formation Process ◽

Organic Molecules ◽

Planet Formation ◽

Protoplanetary Disks ◽

Excitation Temperature ◽

Top Down ◽

Carbon Chemistry ◽

Episodic Nature ◽

Protosolar Nebula

<p>One of the main goals in the fields of exoplanets and planet formation is to determine the composition of terrestrial, potentially habitable, planets and to link this to the composition of protoplanetary disks. A longstanding puzzle in this regard is the Earth's severe carbon deficit; Earth is 2-4 orders of magnitude depleted in carbon compared to interstellar grains and comets. The solution to this conundrum is that carbon must have been returned to the gas phase in the inner protosolar nebula, such that it could not get accreted onto the forming bodies. A process that could be responsible is the sublimation of carbon grains at the so-called soot line (~300 K) early in the planet-formation process. I will argue that the most likely signatures of this process are an excess of hydrocarbons and nitriles inside the soot line around protostars, and a higher excitation temperature for these molecules compared to oxygen-bearing complex organics that desorb around the water snowline (~100 K). Moreover, I will show that such characteristics have indeed been reported in the literature, for example, in Orion KL, although not uniformly, potentially due to differences in observational settings or related to the episodic nature of protostellar accretion. If this process is active, this would mean that there is an heretofore unrecognized component to the carbon chemistry during the protostellar phase that is acting from the top down - starting from the destruction of larger species - instead of from the bottom up from atoms. In the presence of such a top-down component, the origin of organic molecules needs to be re-explored.&#160;</p>

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Laboratory data in support of JWST observations of interstellar ices

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319009827 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 420-421

Author(s):

Marina G. Rachid ◽

Jeroen Terwisscha van Scheltinga ◽

Daniël Koletzki ◽

Giulia Marcandalli ◽

Ewine F. van Dishoeck ◽

...

Keyword(s):

Solid State ◽

Gas Phase ◽

Organic Molecules ◽

Methyl Formate ◽

Laboratory Data ◽

Protoplanetary Disks ◽

Theoretical Studies ◽

James Webb Space Telescope ◽

Complex Organic ◽

Experimental And Theoretical Studies

AbstractExperimental and theoretical studies have shown that Complex Organic Molecules (COMs) can be formed on icy dusty grains in molecular clouds and protoplanetary disks. The number of astronomical detections of solid COMs, however, is very limited. With the upcoming launch of the James Webb Space Telescope (JWST) this should change, but in order to identify solid state features of COMs, accurate laboratory data are needed. Here we present high resolution (0.5 cm–1) infrared ice spectra of acetone (C3H6O) and methyl formate (HCOOCH3), two molecules already identified in astronomical gas phase surveys, whose interstellar synthesis is expected to follow solid state pathways.

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Laboratory constraints on ice formation, restructuring and desorption

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316003136 ◽

2015 ◽

Vol 11 (A29A) ◽

pp. 309-312

Author(s):

Karin I. Öberg

Keyword(s):

Gas Phase ◽

Chemical Reactions ◽

Organic Molecules ◽

Protoplanetary Disks ◽

Ice Formation ◽

Circumstellar Dust ◽

Dust Grains ◽

Complex Molecules ◽

Detailed Understanding ◽

Complex Organic

AbstractIces form on the surfaces of interstellar and circumstellar dust grains though freeze-out of molecules and atoms from the gas-phase followed by chemical reactions. The composition, chemistry, structure and desorption properties of these ices regulate two important aspects of planet formation: the locations of major condensation fronts in protoplanetary disks (i.e. snow lines) and the formation efficiencies of complex organic molecules in astrophysical environments. The latter regulates the availability of prebiotic material on nascent planets. With ALMA it is possible to directly observe both (CO) snowlines and complex organics in protoplanetary disks. The interpretation of these observations requires a detailed understanding of the fundamental ice processes that regulate the build-up, evolution and desorption of icy grain mantles. This proceeding reviews how experiments on thermal CO and N2 ice desorption, UV photodesorption of CO ice, and CO diffusion in H2O ice have been used to guide and interpret astrochemical observations of snowlines and complex molecules.

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Chemical complexity in the Horsehead photodissociation region

Faraday Discussions ◽

10.1039/c3fd00114h ◽

2014 ◽

Vol 168 ◽

pp. 103-127 ◽

Cited By ~ 29

Author(s):

Viviana V. Guzmán ◽

Jérôme Pety ◽

Pierre Gratier ◽

Javier R. Goicoechea ◽

Maryvonne Gerin ◽

...

Keyword(s):

Interstellar Medium ◽

Gas Phase ◽

Thermal Desorption ◽

Organic Molecules ◽

Dense Core ◽

High Spectral Resolution ◽

Complex Molecules ◽

Chemical Complexity ◽

Clean Environment ◽

Complex Organic

The interstellar medium is known to be chemically complex. Organic molecules with up to 11 atoms have been detected in the interstellar medium, and are believed to be formed on the ices around dust grains. The ices can be released into the gas-phase either through thermal desorption, when a newly formed star heats the medium around it and completely evaporates the ices; or through non-thermal desorption mechanisms, such as photodesorption, when a single far-UV photon releases only a few molecules from the ices. The first mechanism dominates in hot cores, hot corinos and strongly UV-illuminated PDRs, while the second dominates in colder regions, such as low UV-field PDRs. This is the case of the Horsehead were dust temperatures are ≃20–30 K, and therefore offers a clean environment to investigate the role of photodesorption. We have carried out an unbiased spectral line survey at 3, 2 and 1mm with the IRAM-30m telescope in the Horsehead nebula, with an unprecedented combination of bandwidth, high spectral resolution and sensitivity. Two positions were observed: the warm PDR and a cold condensation shielded from the UV field (dense core), located just behind the PDR edge. We summarize our recently published results from this survey and present the first detection of the complex organic molecules HCOOH, CH2CO, CH3CHO and CH3CCH in a PDR. These species together with CH3CN present enhanced abundances in the PDR compared to the dense core. This suggests that photodesorption is an efficient mechanism to release complex molecules into the gas-phase in far-UV illuminated regions.

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Complex organic molecules tracing the comet-forming zones in protoplanetary disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319006434 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 463-464

Author(s):

Catherine Walsh ◽

John D. Ilee

Keyword(s):

Gas Phase ◽

Column Density ◽

Organic Molecules ◽

Rotational Temperature ◽

Protoplanetary Disks ◽

Independent Determination ◽

Model Independent ◽

Abundance And Distribution ◽

Complex Organic

AbstractResolved emission from gas-phase methanol can reveal the abundance and distribution of the comet-forming ice reservoir in protoplanetary disks. ALMA Cycle 4 observations of four transitions of gas-phase methanol in TW Hya allow the first model-independent determination of the rotational temperature of methanol in a prototoplanetary disk. The data confirm that the methanol is rotationally cold (Trot < 50 K), and well constrain the column density to 2 × 1012 cm−2. Astrochemical models will constrain the chemical origin of methanol in TW Hya.

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Electronic excitations in ZnWO4 and ZnxNi1−x WO4 (x = 0.1 − 0.9) using VUV synchrotron radiation

Open Physics ◽

10.2478/s11534-010-0108-7 ◽

2011 ◽

Vol 9 (2) ◽

Cited By ~ 8

Author(s):

Aleksandr Kalinko ◽

Alexey Kotlov ◽

Alexei Kuzmin ◽

Vladimir Pankratov ◽

Anatoli Popov ◽

...

Keyword(s):

Synchrotron Radiation ◽

Solid Solutions ◽

Vacuum Ultraviolet ◽

Localized States ◽

Electronic Excitations ◽

Photoluminescence Band ◽

Excitation Spectra ◽

X Ray ◽

Electron Transitions ◽

The One

AbstractThe photoluminescence spectra and luminescence excitation spectra of pure microcrystalline and nano-sized ZnWO4 as well as the ZnxNi1−x WO4 solid solutions were studied using vacuum ultraviolet (VUV) synchrotron radiation. The samples were also characterized by x-ray powder diffraction. We found that: (i) the shape of the photoluminescence band at 2.5 eV, being due to radiative electron transitions within the [WO6]6− anions, becomes modulated by the optical absorption of Ni2+ ions in the ZnxNi1−x WO4 solid solutions; and (ii) no significant change in the excitation spectra of Zn0.9Ni0.1WO4 is observed compared to pure ZnWO4. At the same time, a shift of the excitonic bands to smaller energies and a set of peaks, attributed to the one-electron transitions from the top of the valence band to quasi-localized states, were observed in the excitation spectrum of nano-sized ZnWO4.

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