Figure 2 - uploaded by Nathalie Brouillet
Content may be subject to copyright.
Dimethyl ether (CH3)2O emission map observed with the EVLA toward Orion BN/KL. The synthesized beam, 065 × 051, is shown in red in the lower left corner. The red contours show the 43 GHz continuum emission of the BN object and the radio source I (see Figure 1). Spectra displayed in this figure are observed toward the four main (CH3)2O emission peaks (DME1 to DME4), i.e., in the following directions: the Compact Ridge (bottom right), the Hot Core-SW (top left), the intermediate region linking the Hot Core to the Compact Ridge (bottom left), and the north of the Compact Ridge (top right).
Source publication
We report the first subarcsecond (065 × 051) image of the dimethyl ether molecule, (CH3)2O, toward the Orion Kleinmann-Low nebula. The observations were carried at 43.4 GHz with the Expanded Very Large Array (EVLA). The distribution of the lower energy transition 61, 5-60, 6, EE (E
u = 21 K) mapped in this study is in excellent agreement with the p...
Contexts in source publication
Context 1
... dimethyl ether emission map at 43.447 GHz is shown in Figure 2. The observed four main molecular emission peaks, hereafter DME1, DME2, DME3, and DME4, are located toward the Compact Ridge, the Hot Core southwest (Hot Core-SW), in an intermediate position between the Compact Ridge and the Hot Core-SW, and in the north of the Compact Ridge, respectively. ...
Context 2
... high spectral resolution provided by the WIDAR correla- tor allows us to distinguish between the AA and EE transitions, although the AE and EA transitions are blended (see Table 1). Spectra of the lower energy transitions 6 1,5 -6 0,6 , AA, EE, and AE/EA (E u = 21 K) observed toward the regions DME1 to DME4 are presented in Figure 2. The observed line parame- ters (velocity, intensity) of the detected (CH 3 ) 2 O 6 1,5 -6 0,6 , EE transition are summarized in Table 3. ...
Context 3
... these data, line sets observed simultaneously on the GBT, we estimate T rot ((CH 3 ) 2 O) ∼ 120 K, in agreement with estimates from transitions of HCOOCH 3 of Favre et al. (2011). Note that the brightness temperature of the dimethyl ether line reported here toward the peak of the compact ridge (DME1; see Figure 2) is ∼140 K and that this line is optically thick (τ es- timated to be 2.9), consistent with the rotational temperature in the broader (16 ) GBT beam. Using lines of acetone (CH 3 ) 2 CO in the same GBT spectrum, Goddi et al. (2009) found a rota- tional temperature twice this value, suggesting an origin in the Hot Core. ...
Context 4
... the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), Friedel & Snyder (2008) have imaged the dimethyl ether transition 13 0,13 -12 1,12 (E u = 86 K) with a beam size of 2. 5 × 0. 85. Our observed (CH 3 ) 2 O emission peaks (DME1, DME2, and DME4; see Figure 2) are present in their lower resolution data. 6 CARMA observations reveal a similar LSR velocity at 7.6 km s −1 . ...
Context 5
... EVLA subarcsecond (0. 65 × 0. 51) image of the dimethyl ether clearly reveals a new emission peak DME3, located be- tween the Hot Core-SW and the Compact Ridge (see Figure 2). ...
Context 6
... particular, these share common emission peaks in the north of the Compact Ridge, in the Compact Ridge itself, toward the Hot Core-SW, and toward an intermediate region linking the Hot Core to the Compact Ridge. These four emission regions are shown in Figure 2 (see labels DME1 to DME4 in the present Letter and MF1 to MF4/5 in Favre et al. 2011). Hence the formation of these two molecules must have some relation, regardless whether the mechanism involves gas phase or grain surface formation. ...
Citations
... DEE, C 2 H 5 OC 2 H 5 , and DME are the largest and most abundant of the ethers in the interstellar medium, and are found in high abundance in star-forming regions, called hot molecular gas cores, characterized by gas temperatures exceeding 100 K where a rich chemistry produces observable molecular line emission at (sub) mm wavelength [7]. Some well-known such sources are the Compact Ridge and the Hot Core in Orion [8,9]. The production of DME and DEE in such hot molecular cores has been recently discussed in some detail by Bergatini et al [10]. ...
We report a joint theoretical and experimental investigation on low-energy electron scattering by dimethyl and diethyl ethers. The experimental elastic differential cross sections were measured at impact energies from 1 eV up to 30 eV and scattering angle range of 10° to 130°. Theoretical elastic differential, integral and momentum-transfer cross sections are calculated at impact energies up to 30 eV, employing the Schwinger multichannel method implemented with norm-conserving pseudopotentials, in the static-exchange and static-exchange plus polarization approximations. Our experimental and theoretical results for dimethyl and diethyl ether are compared with previous data for their isomers, ethanol and butanol, respectively. These comparisons reveal that although the cross sections for the ether and its respective alcohol present similar magnitudes, the angular behavior of their differential cross sections shows some significant differences. From the analysis of the integral cross sections for electron scattering by dimethyl and diethyl ether, we observe a broad structure, at around 9.5 eV, which we assign as the overlap of several resonant structures.
... On the other hand, DME and MF are among the most abundant complex organic molecules (where "complex" in astrochemicalj argonr efers to molecules containing at least six atoms) [35] detected in star-forming regions and in prestellar cores. [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] These oxygen-bearing species can be considered to be prebiotic molecules, since they can act as buildingb locks for sugars and other biomolecules. Therefore, the mechanisms of their formation, destruction and distribution in our galaxy is of paramount importance in the development of theories of the origin of lifeonEarth. ...
Long range intermolecular forces play a crucial role in controlling the outcome of ion-molecule chemical reactions, such as those determining the disappearance of organic or inorganic "complex" molecules recently detected in various regions of the interstellar medium due to collisions with abundant interstellar atomic ions (e.g. H+ and He+). Theoretical treatments, e.g. based on simple capture models, are nowadays often adopted to evaluate the collision energy dependence of reactive cross-sections (hereafter indicated as ) and the temperature dependent rate coecients of many ion-molecule reactions. The obtained results are widely used for the modelling of phenomena occurring in dierent natural environments or technological applications such as astrophysical and laboratory plasmas. Here we demonstrate, through a combined experimental and theoretical investigation on a prototype ion-molecule reaction (He+ + methyl formate), that the dynamics, investigated in detail, shows some intriguing features that can lead to rate coecients at odds with the expectations (e.g. Arrhenius vs anti-Arrhenius behaviours). Therefore, this study casts light on some new and general guidelines to be properly taken into account for a suitable evaluation of rate coecients of ion-molecule reactions.
... The molecular lines and chemistry in Orion-KL have been extensively studied by numerous groups (Sutton et al. 1985(Sutton et al. , 1995Menten et al. 1986;Blake et al. 1987;Turner 1989Turner , 1991Mangum et al. 1990;Minh et al. 1993;Groesbeck 1995;Dickens et al. 1997;Schilke et al. 1997Schilke et al. , 2001Slysh et al. 1999;Ikeda et al. 2001;Lee et al. 2001;Liu et al. 2001Liu et al. , 2002Alakoz et al. 2002;Minier & Booth 2002;White et al. 2003;Beuther et al. 2004Beuther et al. , 2006Charnley 2004;Comito et al. 2005;Friedel et al. 2005;Persson et al. 2007;Friedel & Snyder 2008;Remijan et al. 2008;Goddi et al. 2009;Crockett et al. 2010;Gupta et al. 2010;Margulès et al. 2010;Favre et al. 2011aFavre et al. , 2011bZapata et al. 2011;Friedel & Widicus Weaver 2012;Brouillet et al. 2013;Crockett et al. 2014;Favre et al. 2014;Frayer et al. 2015;Morris et al. 2016;Suzuki et al. 2016;Tahani et al. 2016). We observed this source with a pointing centered on the Orion Hot Core as described by Blake et al. (1986). ...
Spectral line surveys are an indispensable tool for exploring the physical and chemical evolution of astrophysical environments due to the vast amount of data that can be obtained in a relatively short amount of time. We present deep, broadband spectral line surveys of 30 interstellar clouds using two broadband λ = 1.3 mm receivers at the Caltech Submillimeter Observatory. This information can be used to probe the influence of physical environment on molecular complexity. We observed a wide variety of sources to examine the relative abundances of organic molecules as they relate to the physical properties of the source (i.e., temperature, density, dynamics, etc.). The spectra are highly sensitive, with noise levels ≤25 mK at a velocity resolution of ~0.35 km s⁻¹. In the initial analysis presented here, column densities and rotational temperatures have been determined for the molecular species that contribute significantly to the spectral line density in this wavelength regime. We present these results and discuss their implications for complex molecule formation in the interstellar medium.
Methanol is one of the most abundant interstellar Complex Organic Molecules (iCOMs) and represents a major building block for the synthesis of increasingly complex oxygen-containing molecules. The reaction between protonated methanol and its neutral counterpart, giving protonated dimethyl ether, (CH3)2OH+
, along with the ejection of a water molecule, has been proposed as a key reaction in the synthesis of dimethyl ether in space.
Here, gas phase vibrational spectra of the (CH3)2OH+
reaction product and the [C2H9O2]+ intermediate complex(es), formed under different pressure and temperature conditions, are presented. The widely tunable free electron laser for infrared experiments, FELIX, was employed to record these vibrational fingerprint spectra using different types of infrared action spectroscopy in the 600-1700 cm−1 frequency range, complemented with measurements using an OPO/OPA system to cover the O−H stretching region 3400−3700cm−1. The formation of protonated dimethyl ether as a product of the reaction is spectroscopically confirmed, providing the first gas-phase vibrational spectrum of this potentially relevant astrochemical ion.
Laboratory astrochemists have generated infrared (IR) data for nearly all common classes of organic compounds, but ethers in the solid phase continued to be neglected despite detections of ethers in the interstellar medium by radio astronomers and uncertainty in how extraterrestrial ethers are formed. To address this paucity of data, here we present new mid-IR spectra of amorphous and crystalline dimethyl ether, (CH3)2O, the simplest member of its class. Spectral positions are tabulated and compared to previous results, but more importantly we also report IR band strengths and absorption coefficients, which we have not found in the literature and on which quantitative IR studies depend. Optical constants of amorphous and crystalline dimethyl ether also have been calculated. Some applications are described.
We investigate the chemical segregation of complex O-bearing species (including the largest and most complex ones detected to date in space) towards Orion KL, the closest high-mass star-forming region. The molecular line images obtained using the ALMA science verification data reveal a clear segregation of chemically related species depending on their different functional groups. We map the emission of ¹³CH3OH, HCOOCH3, CH3OCH3, CH2OCH2, CH3COOCH3, HCOOCH2CH3, CH3CH2OCH3, HCOOH, OHCH2CH2OH, CH3COOH, CH3CH2OH, CH3OCH2OH, OHCH2CHO, and CH3COCH3 with ∼1.5″ angular resolution and provide molecular abundances of these species toward different gas components of this region. We disentangle the emission of these species in the different Orion components by carefully selecting lines free of blending and opacity effects. Possible effects in the molecular spatial distribution due to residual blendings and different excitation conditions are also addressed. We find that while species containing the C-O-C group, i.e. an ether group, exhibit their peak emission and higher abundance towards the compact ridge, the hot core south is the component where species containing a hydroxyl group (-OH) bound to a carbon atom (C-O-H) present their emission peak and higher abundance. This finding allows us to propose methoxy (CH3O-) and hydroxymethyl (-CH2OH) radicals as the major drivers of the chemistry in the compact ridge and the hot core south, respectively, as well as different evolutionary stages and prevailing physical processes in the different Orion components.
Context:
Methoxyacetaldehyde belongs to a group of structural isomers with the general formula C3H6O2, of which methyl acetate and ethyl formate are known interstellar molecules. Rotational data available for methoxyacetaldehyde are limited to 40 GHz, which makes predictions at higher frequencies rather uncertain.
Aims:
The aim of this work is to provide accurate experimental frequencies of methoxyacetaldehyde in the millimeter-wave region to support its detection in the interstellar medium.
Methods:
The rotational spectrum of methoxyacetaldehyde was recorded at room-temperature from 75 to 120 GHz and from 170 to 310 GHz using the millimeter-wave spectrometer in Valladolid. Additional measurements were also performed at conditions of supersonic expansion from 6 to 18 GHz. The assigned rotational transitions were analyzed using the S -reduced semirigid-rotor Hamiltonian.
Results:
We newly assigned over 1000 lines for the most stable conformer of methoxyacetaldehyde in its ground state and five lowest excited vibrational states, and precise sets of spectroscopic constants were obtained. We searched for spectral features of methoxyacetaldehyde in the high-mass star-forming regions Orion KL and Sagittarius B2, as well as in the cold dark cloud Barnard 1 (B1-b). No lines belonging to methoxyacetaldehyde were detected above the detection limit of our data. We provide upper limits to the methoxyacetaldehyde colum density in these sources.
Context. About 40 cyanide compounds have been detected in the interstellar medium, but only 3 examples of organic isocyanide compounds were observed in this medium. Ethyl isocyanide is one of the best candidates for possible detection.
Aim. To date, measurements of rotational spectra are limited to 40 GHz. The extrapolation of the prediction in the millimeter wave domain is inaccurate and does not permit an unambiguous detection.
Methods. The rotational spectra were reinvestigated from 0.15 to 1 THz. Using the new prediction, we searched for the compound ethyl isocyanide in Orion KL and Sgr B2.
Results. We newly assigned 2906 transitions and fitted these new data with those from previous studies, reaching quantum numbers up to J = 103 and K a = 30. The asymmetric top Hamiltonian proposed by Watson in the I r representation was used for the analysis, and both reductions A and S were tested. The search for CH 3 CH 2 NC in Sgr B2 (IRAM 30m) and Orion KL (IRAM 30m, ALMA Science Verification) result in a non-detection; upper limits to the column density were derived.
Aims:
Methoxyamine is a potential interstellar amine that has been predicted by gas-grain chemical models for the formation of complex molecules. The aim of this work is to provide direct experimental frequencies of its ground-vibrational state in the millimeter- and submillimeter-wave regions to achieve its detection in the interstellar medium.
Methods:
Methoxyamine was chemically liberated from its hydrochloride salt, and its rotational spectrum was recorded at room temperature from 75 to 480 GHz using the millimeter-wave spectrometer in Valladolid. Many observed transitions revealed A-E splitting caused by the internal rotation of the methyl group, which had to be treated with specific internal rotation codes.
Results:
Over 400 lines were newly assigned for the most stable conformer of methoxyamine, and a precise set of spectroscopic constants was obtained. Spectral features of methoxyamine were then searched for in the Orion KL, Sgr B2, B1-b, and TMC-1 molecular clouds. Upper limits to the column density of methoxyamine were derived.
We present sensitive high angular resolution ($\sim$ 0.1$''$ -- 0.3$''$) continuum ALMA (The Atacama Large Millimeter/Submillimeter Array) observations of the archetypal hot core located in Orion-KL. The observations were made in five different spectral bands (bands 3, 6, 7, 8, and 9) covering a very broad range of frequencies (149 -- 658 GHz). Apart of the well-know millimeter emitting objects located in this region (Orion Source I and BN), we report the first submillimeter detection of three compact continuum sources (ALMA 1-3) in the vicinities of the Orion-KL hot molecular core. These three continuum objects have spectral indices between 1.47 to 1.56, and brightness temperatures between 100 to 200 K at 658 GHz suggesting that we are seeing moderate optically thick dust emission with possible grain growth. However, as these objects are not associated with warm molecular gas, and some of them are farther out from the molecular core, we thus conclude that they cannot heat the molecular core. This result favours the hypothesis that the hot molecular core in Orion-KL core is heated externally.
