scholarly journals Nonadiabatic reaction dynamics to silicon monosulfide (SiS): A key molecular building block to sulfur-rich interstellar grains

2021 ◽  
Vol 7 (26) ◽  
pp. eabg7003
Author(s):  
Srinivas Doddipatla ◽  
Chao He ◽  
Shane J. Goettl ◽  
Ralf I. Kaiser ◽  
Breno R. L. Galvão ◽  
...  
Keyword(s):  
Gas Phase ◽  
Reaction Dynamics ◽  
Formation Mechanisms ◽  
Phase Reaction ◽  
Sulfur Chemistry ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Circumstellar Environments ◽  
A Chain

Sulfur- and silicon-containing molecules are omnipresent in interstellar and circumstellar environments, but their elementary formation mechanisms have been obscure. These routes are of vital significance in starting a chain of chemical reactions ultimately forming (organo) sulfur molecules—among them precursors to sulfur-bearing amino acids and grains. Here, we expose via laboratory experiments, computations, and astrochemical modeling that the silicon-sulfur chemistry can be initiated through the gas-phase reaction of atomic silicon with hydrogen sulfide leading to silicon monosulfide (SiS) via nonadiabatic reaction dynamics. The facile pathway to the simplest silicon and sulfur diatomic provides compelling evidence for the origin of silicon monosulfide in star-forming regions and aids our understanding of the nonadiabatic reaction dynamics, which control the outcome of the gas-phase formation in deep space, thus expanding our view about the life cycle of sulfur in the galaxy.

scholarly journals A chemical dynamics study on the gas phase formation of thioformaldehyde (H2CS) and its thiohydroxycarbene isomer (HCSH)

2020 ◽  
Vol 117 (37) ◽  
pp. 22712-22719 ◽  
Author(s):  
Srinivas Doddipatla ◽  
Chao He ◽  
Ralf I. Kaiser ◽  
Yuheng Luo ◽  
Rui Sun ◽  
...  
Keyword(s):  
Gas Phase ◽  
Iron Sulfide ◽  
Classical Trajectory ◽  
Structure Theory ◽  
Formation Mechanisms ◽  
Phase Reaction ◽  
Origin And Evolution ◽  
Star Forming ◽  
Star Forming Regions ◽  
Interstellar Molecular Clouds

Complex organosulfur molecules are ubiquitous in interstellar molecular clouds, but their fundamental formation mechanisms have remained largely elusive. These processes are of critical importance in initiating a series of elementary chemical reactions, leading eventually to organosulfur molecules—among them potential precursors to iron-sulfide grains and to astrobiologically important molecules, such as the amino acid cysteine. Here, we reveal through laboratory experiments, electronic-structure theory, quasi-classical trajectory studies, and astrochemical modeling that the organosulfur chemistry can be initiated in star-forming regions via the elementary gas-phase reaction of methylidyne radicals with hydrogen sulfide, leading to thioformaldehyde (H2CS) and its thiohydroxycarbene isomer (HCSH). The facile route to two of the simplest organosulfur molecules via a single-collision event affords persuasive evidence for a likely source of organosulfur molecules in star-forming regions. These fundamental reaction mechanisms are valuable to facilitate an understanding of the origin and evolution of the molecular universe and, in particular, of sulfur in our Galaxy.

scholarly journals A study of interstellar aldehydes and enols as tracers of a cosmic ray-driven nonequilibrium synthesis of complex organic molecules

2016 ◽  
Vol 113 (28) ◽  
pp. 7727-7732 ◽  
Author(s):  
Matthew J. Abplanalp ◽  
Samer Gozem ◽  
Anna I. Krylov ◽  
Christopher N. Shingledecker ◽  
Eric Herbst ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Cosmic Ray ◽  
Formation Mechanisms ◽  
Molecular Precursors ◽  
Star Forming ◽  
Star Forming Regions ◽  
Interstellar Ices ◽  
A Chain ◽  
Nonequilibrium Chemistry ◽  
Complex Organic

Complex organic molecules such as sugars and amides are ubiquitous in star- and planet-forming regions, but their formation mechanisms have remained largely elusive until now. Here we show in a combined experimental, computational, and astrochemical modeling study that interstellar aldehydes and enols like acetaldehyde (CH3CHO) and vinyl alcohol (C2H3OH) act as key tracers of a cosmic-ray-driven nonequilibrium chemistry leading to complex organics even deep within low-temperature interstellar ices at 10 K. Our findings challenge conventional wisdom and define a hitherto poorly characterized reaction class forming complex organic molecules inside interstellar ices before their sublimation in star-forming regions such as SgrB2(N). These processes are of vital importance in initiating a chain of chemical reactions leading eventually to the molecular precursors of biorelevant molecules as planets form in their interstellar nurseries.

scholarly journals Processed and Unprocessed Ices in Circumstellar Disks

2005 ◽  
Vol 13 ◽  
pp. 479-481
Author(s):  
Klaus Pontoppidan ◽  
Ewine van Dishoeck ◽  
Emmanuel Dartois ◽  
Wing-Fai Thi
Keyword(s):  
Circumstellar Disks ◽  
High Mass ◽  
Formation Mechanisms ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Solar Type ◽  
Low Mass ◽  
Circumstellar Environments

AbstractWe present 3-5 µm VLT-ISAAC spectroscopy showing the presence of methanol ices in edge-on disks of young embedded stars. Examples include the disks of L1489 IRS in Taurus and CRBR 2422.8-3423 in Ophiuchus, the last of which has the highest column density of solid CO known toward a YSO. Several additional low-mass sources in the Serpens and Chameleon molecular clouds exhibit abundant solid methanol although it is not clear if the ice is associated with a disk or with the envelope. These are the first detections of solid methanol in the disks and circumstellar environments of embedded young low-mass stars providing evidence that complex molecular species previously observed only in the solid state toward high-mass star forming regions are also present near solar-type young stars. The constraints on the formation mechanisms of methanol and the chemical evolution of ices as the material is incorporated into circumstellar disks are discussed.

scholarly journals Very Low-Luminosity Objects in Star-Forming Regions

1998 ◽  
Vol 11 (1) ◽  
pp. 423-424
Author(s):  
Motohide Tamura ◽  
Yoichi Itoh ◽  
Yumiko Oasa ◽  
Alan Tokunaga ◽  
Koji Sugitani
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
T Tauri Stars ◽  
Initial Mass Function ◽  
Formation Mechanisms ◽  
Star Forming ◽  
Star Forming Regions ◽  
T Tauri ◽  
Low Mass ◽  
Stellar Sources

Abstract In order to tackle the problems of low-mass end of the initial mass function (IMF) in star-forming regions and the formation mechanisms of brown dwarfs, we have conducted deep infrared surveys of nearby molecular clouds. We have found a significant population of very low-luminosity sources with IR excesses in the Taurus cloud and the Chamaeleon cloud core regions whose extinction corrected J magnitudes are 3 to 8 mag fainter than those of typical T Tauri stars in the same cloud. Some of them are associated with even fainter companions. Follow-up IR spectroscopy has confirmed for the selected sources that their photospheric temperature is around 2000 to 3000 K. Thus, these very low-luminosity young stellar sources are most likely very low-mass T Tauri stars, and some of them might even be young brown dwarfs.

scholarly journals Gas phase formation of c-SiC3molecules in the circumstellar envelope of carbon stars

2019 ◽  
Vol 116 (29) ◽  
pp. 14471-14478 ◽  
Author(s):  
Tao Yang ◽  
Luke Bertels ◽  
Beni B. Dangi ◽  
Xiaohu Li ◽  
Martin Head-Gordon ◽  
...  
Keyword(s):  
Carbon Star ◽  
Asymptotic Giant Branch ◽  
Formation Mechanisms ◽  
Circumstellar Envelope ◽  
Outer Envelope ◽  
Parent Molecule ◽  
Silicon Carbon ◽  
Electronically Excited ◽  
Circumstellar Environments ◽  
A Chain

Complex organosilicon molecules are ubiquitous in the circumstellar envelope of the asymptotic giant branch (AGB) star IRC+10216, but their formation mechanisms have remained largely elusive until now. These processes are of fundamental importance in initiating a chain of chemical reactions leading eventually to the formation of organosilicon molecules—among them key precursors to silicon carbide grains—in the circumstellar shell contributing critically to the galactic carbon and silicon budgets with up to 80% of the ejected materials infused into the interstellar medium. Here we demonstrate via a combined experimental, computational, and modeling study that distinct chemistries in the inner and outer envelope of a carbon star can lead to the synthesis of circumstellar silicon tricarbide (c-SiC3) as observed in the circumstellar envelope of IRC+10216. Bimolecular reactions of electronically excited silicon atoms (Si(1D)) with allene (H2CCCH2) and methylacetylene (CH3CCH) initiate the formation of SiC3H2molecules in the inner envelope. Driven by the stellar wind to the outer envelope, subsequent photodissociation of the SiC3H2parent operates the synthesis of the c-SiC3daughter species via dehydrogenation. The facile route to silicon tricarbide via a single neutral–neutral reaction to a hydrogenated parent molecule followed by photochemical processing of this transient to a bare silicon–carbon molecule presents evidence for a shift in currently accepted views of the circumstellar organosilicon chemistry, and provides an explanation for the previously elusive origin of circumstellar organosilicon molecules that can be synthesized in carbon-rich, circumstellar environments.

scholarly journals The Circumstellar Environment of Embedded Massive Stars

2002 ◽  
Vol 12 ◽  
pp. 143-145 ◽  
Author(s):  
Lee G. Mundy ◽  
Friedrich Wyrowski ◽  
Sarah Watt
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Submillimeter Wavelength ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Circumstellar Environments ◽  
Near Future

Millimeter and submillimeter wavelength images of massive star-forming regions are uncovering the natal material distribution and revealing the complexities of their circumstellar environments on size scales from parsecs to 100’s of AU. Progress in these areas has been slower than for low-mass stars because massive stars are more distant, and because they are gregarious siblings with different evolutionary stages that can co-exist even within a core. Nevertheless, observational goals for the near future include the characterization of an early evolutionary sequence for massive stars, determination if the accretion process and formation sequence for massive stars is similar to that of low-mass stars, and understanding of the role of triggering events in massive star formation.

scholarly journals Dust in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 57-62
Author(s):  
Paul Hodge
Keyword(s):  
Heavy Element ◽  
Magellanic Clouds ◽  
Dust Content ◽  
Optical Observations ◽  
Optical Data ◽  
Star Forming ◽  
Element Abundances ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Far Ultraviolet

The dust content of the Magellanic Clouds can be studied using optical, ultraviolet, infrared and, indirectly, radio wavelength data. All recent studies show that the dust content is lower than that of the Milky Way Galaxy for both Clouds and that the optical properties of the dust are different. At ultraviolet wavelengths, the 2165 Å “bump” in the extinction curve is significantly smaller than in the Galaxy (this now appears NOT to be a consequence of the lower heavy element abundances) and the far ultraviolet (shortward of ˜2000 Å) extinction is greater than in the Galaxy (this IS likely to be a consequence of the lower heavy element abundances). New optical data on background galaxies suggest that the total extinction in the central parts of both the LMC and the SMC is approximately 1.5 magnitudes. High local extinction values are derived from uv and optical observations of star-forming regions, where a spatial correlation with CO detections is sometimes, but not always, found.

scholarly journals Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey

1987 ◽  
Vol 115 ◽  
pp. 499-499 ◽  
Author(s):  
P. M. Solomon
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Formation Mechanisms ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
Two Populations ◽  
Spiral Arm

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.

scholarly journals DMS oxidation and sulfur aerosol formation in the marine troposphere: a focus on reactive halogen and multiphase chemistry

2018 ◽  
Vol 18 (18) ◽  
pp. 13617-13637 ◽  
Author(s):  
Qianjie Chen ◽  
Tomás Sherwen ◽  
Mathew Evans ◽  
Becky Alexander
Keyword(s):  
Gas Phase ◽  
Dimethyl Sulfide ◽  
Transport Model ◽  
Removal Rate ◽  
Sulfur Cycle ◽  
Phase Reaction ◽  
Aerosol Formation ◽  
Cloud Droplets ◽  
Sulfur Chemistry ◽  
Marine Troposphere

Abstract. The oxidation of dimethyl sulfide (DMS) in the troposphere and subsequent chemical conversion into sulfur dioxide (SO2) and methane sulfonic acid (MSA) are key processes for the formation and growth of sulfur-containing aerosol and cloud condensation nuclei (CCN), but are highly simplified in large-scale models of the atmosphere. In this study, we implement a series of gas-phase and multiphase sulfur oxidation mechanisms into the Goddard Earth Observing System-Chemistry (GEOS-Chem) global chemical transport model – including two important intermediates, dimethyl sulfoxide (DMSO) and methane sulphinic acid (MSIA) – to investigate the sulfur cycle in the global marine troposphere. We found that DMS is mainly oxidized in the gas phase by OH (66 %), NO3 (16 %) and BrO (12 %) globally. DMS + BrO is important for the model's ability to reproduce the observed seasonality of surface DMS mixing ratio in the Southern Hemisphere. MSA is mainly produced from multiphase oxidation of MSIA by OH(aq) (66 %) and O3(aq) (30 %) in cloud droplets and aerosols. Aqueous-phase reaction with OH accounts for only 12 % of MSA removal globally, and a higher MSA removal rate is needed to reproduce observations of the MSA ∕ nssSO42- ratio. The modeled conversion yield of DMS into SO2 and MSA is 75 % and 15 %, respectively, compared to 91 % and 9 % in the standard model run that includes only gas-phase oxidation of DMS by OH and NO3. The remaining 10 % of DMS is lost via deposition of intermediates DMSO and MSIA. The largest uncertainties for modeling sulfur chemistry in the marine boundary layer (MBL) are unknown concentrations of reactive halogens (BrO and Cl) and OH(aq) concentrations in cloud droplets and aerosols. To reduce uncertainties in MBL sulfur chemistry, we should prioritize observations of reactive halogens and OH(aq).

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