- ID:
- ivo://CDS.VizieR/J/A+A/562/A56
- Title:
- Cyanomethyl anion and its deuterated derivatives
- Short Name:
- J/A+A/562/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has long been suggested that CH_2_CN^-^ (cyanomethyl anion) might be a carrier of one of the many poorly characterized diffuse interstellar bands. In this paper, our aim is to study various forms (ionic, neutral, and deuterated isotopomer) of CH_2_CN (cyanomethyl radical) in the interstellar medium. The aim of this paper is to predict spectroscopic characteristics of various forms of CH_2_CN and its deuterated derivatives. Moreover, we would like to model the interstellar chemistry for predicting the column densities of such species around dark cloud conditions.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/724/994
- Title:
- Cyano- to methanol and ammonia observations
- Short Name:
- J/ApJ/724/994
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of an effort to study gas-grain chemical models in star-forming regions as they relate to molecules containing cyanide (-C{\equiv}N) groups, we present here a search for the molecules 2-cyanoethanol (OHCH_2_CH_2_CN) and methoxyacetonitrile (CH_3_OCH_2_CN) in the galactic center region SgrB2. These species are structural isomers of each other and are targeted to investigate the cross-coupling of pathways emanating from the photolysis products of methanol and ammonia with pathways involving cyano-containing molecules. Methanol and ammonia ices are two of the main repositories of the elements C, O, and N in cold clouds and understanding their link to cyanide chemistry could give important insights into prebiotic molecular evolution. Neither species was positively detected, but the upper limits we determined allow comparison to the general patterns gleaned from chemical models. Our results indicate the need for an expansion of the model networks to better deal with cyano-chemistry, in particular with respect to pathways including products of methanol photolysis. In addition to these results, the two main observational routes for detecting new interstellar molecules are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/472/1029
- Title:
- (De)excitation rates of H2O by H2
- Short Name:
- J/A+A/472/1029
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interpretation of water line emission from existing observations and future HIFI/Herschel data requires a detailed knowledge of collisional rate coefficients. Among all relevant collisional mechanisms, the rotational (de)excitation of H2O by H2 molecules is the process of most interest in interstellar space. We provide rate coefficients for rotational de-excitation among the lowest 45 para and 45 ortho rotational levels of H2O colliding with both para and ortho-H2 in the temperature range 20-2000K. Rate coefficients are calculated on a recent high-accuracy H2O-H2 potential energy surface using quasi-classical trajectory calculations. Trajectories are sampled by a canonical Monte-Carlo procedure. H2 molecules are assumed rotationally thermalized at the kinetic temperature. By comparison with quantum calculations available for low lying levels, classical rates are found to be accurate within a factor of 1-3 for the dominant transitions, that is those with rates larger than a few 10^-12^cm^3^/s. Large velocity gradient modelling shows that the new rates have a significant impact on emission line fluxes and that they should be adopted in any detailed population model of water in warm and hot environments.
- ID:
- ivo://CDS.VizieR/J/MNRAS/399/425
- Title:
- (De)excitation rates of ortho-NH3 and para-NH3
- Short Name:
- J/MNRAS/399/425
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ammonia inversion lines are often used as probes of the physical conditions in the dense ISM. The excitation temperature between the first two para metastable (rotational) levels is an excellent probe of the gas kinetic temperature. However, the calibration of this ammonia thermometer depends on the accuracy of the collisional rates with H2. Here we present new collisional rates for ortho-NH3 and para-NH3 colliding with para-H2 (J=0) and we investigate the effects of these new rates on the excitation of ammonia. Scattering calculations employ a new, high accuracy, potential energy surface computed at the coupled-cluster CCSD(T) level with a basis set extrapolation procedure. Rates are obtained for all transitions involving ammonia levels with J<=3 and for kinetic temperatures in the range 5-100K. We find that the calibration curve of the ammonia thermometer -- which relates the observed excitation temperature between the first two para metastable levels to the gas kinetic temperature -- does not change significantly when these new rates are used. Thus, the calibration of ammonia thermometer appears to be robust. Effects of the new rates on the excitation temperature of inversion and rotation-inversion transitions are also found to be small.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/L13
- Title:
- Detection of CH_3_COOCH_3_ in Orion
- Short Name:
- J/ApJ/770/L13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of methyl acetate, CH_3_COOCH_3_, through the detection of a large number of rotational lines from each one of the spin states of the molecule: AA species (A_1_ or A_2_), EA species (E_1_), AE species (E_2_), and EE species (E_3_ or E_4_). We also report, for the first time in space, the detection of the gauche conformer of ethyl formate, CH_3_CH_2_OCOH, in the same source. The trans conformer is also detected for the first time outside the Galactic center source SgrB2. From the derived velocity of the emission of methyl acetate, we conclude that it arises mainly from the compact ridge region with a total column density of (4.2+/-0.5)x10^15^/cm2. The derived rotational temperature is 150K. The column density for each conformer of ethyl formate, trans and gauche, is (4.5+/-1.0)x10^14^/cm2. Their abundance ratio indicates a kinetic temperature of 135K for the emitting gas and suggests that gas-phase reactions could participate efficiently in the formation of both conformers in addition to cold ice mantle reactions on the surface of dust grains.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A96
- Title:
- Detection of the propargyl radical at lambda 3mm
- Short Name:
- J/A+A/657/A96
- Date:
- 21 Mar 2022 09:30:15
- Publisher:
- CDS
- Description:
- We report the detection of the propargyl radical (CH_2_CCH) in the cold dark cloud TMC-1 in the lambda 3mm wavelength band. We recently discovered this species in space toward the same source at a wavelength of lambda 8mm. In those observations, various hyperfine components of the 202-101 rotational transition, at 37.5GHz, were detected using the Yebes 40m telescope. Here, we used the IRAM 30m telescope to detect ten hyperfine components of the 505-404 rotational transition, lying at 93.6GHz. The observed frequencies differ by 0.2MHz with respect to the predictions from available laboratory data. This difference is significant for a radioastronomical search for CH_2_CCH in interstellar sources with narrow lines. We thus included the measured frequencies in a new spectroscopic analysis to provide accurate frequency predictions for the interstellar search for propargyl at mm wavelengths. Moreover, we recommend that future searches for CH_2_CCH in cold interstellar clouds are carried out at lambda 3mm, rather than at lambda 8 mm. The 505-404 transition is about five times more intense than the 202-101 transition in TMC-1, which implies that detecting the former requires about seven times less telescope time than detecting the latter. We constrain the rotational temperature of CH_2_CCH in TMC-1 to 9.9+/-1.5K, which indicates that the rotational levels of this species are thermalized at the gas kinetic temperature. The revised value of the column density of CH_2_CCH (including ortho and para species) is (1.0+/-0.2)x10^14^cm^-2^, and thus the CH_2_CCH/CH_3_CCH abundance ratio is revised from slightly below one to nearly one. This study opens the door for future detections of CH_2_CCH in other cold interstellar clouds, making possible to further investigate the role of this very abundant hydrocarbon radical in the synthesis of large organic molecules such as aromatic rings.
- ID:
- ivo://CDS.VizieR/J/A+A/493/565
- Title:
- Deuterated and ^15^N ethyl cyanides
- Short Name:
- J/A+A/493/565
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ethyl cyanide is an abundant molecule in hot molecular clouds. Its rotational spectrum is very dense and several hundreds of rotational transitions within the ground state have been identified in molecular clouds in the 40-900GHz frequency range. Lines from ^13^C isotopically substituted ethyl cyanide have been recently identified in Orion. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects we have studied the rotational spectrum of deuterated ethyl cyanide: CH_2_DCH_2_CN (in-plane and out-of-plane) and CH_3_CHDCN and the spectrum of ^15^N substituted ethyl cyanide CH_2_DCH_2_C^15^N. The rotational spectrum of these species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using waveguide Fourier transform spectrometers (4-40GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150-260 and 580-660GHz). More than 300 lines were identified for each species for J values up to 71-80 and K_a_ values up to 28-31 depending on the isotopologues. The experimental spectra were analysed using a Watson's Hamiltonian using A-reduction in I^r^ representation. From the fitting procedure, accurate spectroscopic constants were derived for each species. These new sets of spectroscopic constants enable us to compute reliable prediction of the rotational spectrum (lines frequency and intensity) in the 4-1000GHz frequency range and for J and K_a_ up to 80 and 31, respectively. This experimental study allowed us to detect for the first time ^15^N substituted ethyl cyanide CH_2_DCH_2_C^15^N in Orion. The derived column density and rotational temperature are 10^13^cm^-2^ and 150K for the plateau and 3x10^14^cm^-2^ and 300K for the hot core. The deuterated species were search for but are not detected. The upper limit on the column density of each deuterated isotopologues is 10^14^cm^-2^.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/44
- Title:
- Deuterated chemistry of the early universe
- Short Name:
- J/ApJ/737/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comprehensive chemistry of the highly deuterated species D_2_, D^+^_2_, D_2_H^+^, and D^+^_3_ in the early universe is presented. Fractional abundances for each are calculated as a function of redshift z in the recombination era. The abundances of the isotopologues are found to display similar behavior. Fractionation enhances the abundances of most of the more highly deuterated species as the redshift decreases due to the closing of some reaction channels as the gas temperature cools. Rate coefficients for the majority of the reactions involving the deuterated species are uncertain resulting in a corresponding uncertainty in their predicted abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/376/356
- Title:
- Diatomic molecules collisional rates
- Short Name:
- J/A+A/376/356
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A number of diatomic molecules have been found in vibrationally excited states in several cosmic objects. The molecules in vibrationally excited states provide valuable information about the physical conditions prevailing near star forming regions and in circumstellar envelopes of late-type stars. To analyze the spectrum of such molecules, some of the important parameters required are the collisional rate coefficients for vib-rotational transitions in the molecule. Currently, knowledge of collisional rate coefficients is very poor. Here, we discuss a method for calculating the collisional rate coefficients for vib-rotational transitions in a diatomic molecule, where the colliding partner H_2_ is considered as a structureless particle. This method is quite good for high temperatures (usually found in star-forming regions and in circumstellar envelopes of late-type stars), but may be questioned for low temperatures. As an example, calculations for the CS molecule at 500K for three vibrational states are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/659/A69
- Title:
- Di-deuterated methanol (CHD2OH) line list
- Short Name:
- J/A+A/659/A69
- Date:
- 14 Mar 2022 07:43:58
- Publisher:
- CDS
- Description:
- Di-deuterated molecules are observed in the earliest stages of star formation at abundances of a few percent relative to their nondeuterated isotopologs, which is unexpected considering the scarcity of deuterium in the interstellar medium. With sensitive observations leading to the detection of a steadily increasing number of di-deuterated species, it is becoming possible to explore successive deuteration chains. The accurate quantification of the column density of di-deuterated methanol is a key piece of the puzzle that is missing in the otherwise thoroughly constrained family of D-bearing methanol in the deeply embedded low-mass protostellar system and astrochemical template source IRAS 16293-2422. A spectroscopic dataset for astrophysical purposes was built for CHD2OH and made publicly available to facilitate the accurate characterization of this species in astrochemical surveys. The newly computed line list and partition function were used to search for CHD_2_OH toward IRAS 16293-2422 A and B in data from the Atacama Large Millimeter/submillimeter Array (ALMA) Protostellar Interferometric Line Survey (PILS). Only nonblended, optically thin lines of CHD_2_OH were used for the synthetic spectral fitting. The constructed spectroscopic database contains line frequencies and strengths for 7417 transitions in the 0-500GHz frequency range. ALMA-PILS observations in the 329-363GHz range were used to identify 105 unique, nonblended, optically thin line frequencies of CHD2OH for synthetic spectral fitting. The derived excitation temperatures and column densities yield high D/H ratios of CHD2OH in IRAS 16293-2422 A and B of 7.5+/-1.1% and 7.7+/-1.2%, respectively. Deuteration in IRAS 16293-2422 is not higher than in other low-mass star-forming regions (L483, SVS13-A, NGC 1333-IRAS2A, -IRAS4A, and -IRAS4B). Di-deuterated molecules consistently have higher D/H ratios than their mono-deuterated counterparts in all low-mass protostars, which may be a natural consequence of H-D substitution reactions as seen in laboratory experiments. The Solar System's natal cloud, as traced by comet 67P/Churyumov-Gerasimenko, may have had a lower initial abundance of D, been warmer than the cloud of IRAS 16293-2422, or been partially reprocessed. In combination with accurate spectroscopy, a careful spectral analysis, and the consideration of the underlying assumptions, successive deuteration is a robust window on the physicochemical provenance of star-forming systems.
