47 research outputs found
New quantum chemical computations of formamide deuteration support a gas-phase formation of this prebiotic molecule
Based on recent work, formamide might be a potentially very important
molecule in the emergence of terrestrial life. Although detected in the
interstellar medium for decades, its formation route is still debated, whether
in the gas phase or on the dust grain surfaces. Molecular deuteration has
proven to be, in other cases, an efficient way to identify how a molecule is
synthesised. For formamide, new published observations towards the
IRAS16293-2422 B hot corino show that its three deuterated forms have all the
same deuteration ratio, 2--5%, and that this is a factor 3--8 smaller than that
measured for H2CO towards the IRAS16293-2422 protostar. Following a previous
work on the gas-phase formamide formation via the reaction NH2 + H2CO -> HCONH2
+ H, we present here new calculations of the rate coefficients for the
production of monodeuterated formamide through the same reaction, starting from
monodeuterated NH2 or H2CO. Some misconceptions regarding our previous
treatment of the reaction are also cleared up. The results of the new
computations show that, at the 100 K temperature of the hot corino, the rate of
deuteration of the three forms is the same, within 20%. On the contrary, the
reaction between non-deuterated species proceeds three times faster than that
with deuterated ones. These results confirm that a gas-phase route for the
formation of formamide is perfectly in agreement with the available
observations.Comment: MNRAS in pres
Gas phase formation of the prebiotic molecule formamide: insights from new quantum computations
New insights into the formation of interstellar formamide, a species of great
relevance in prebiotic chemistry, are provided by electronic structure and
kinetic calculations for the reaction NH2 + H2CO -> NH2CHO + H. Contrarily to
what previously suggested, this reaction is essentially barrierless and can,
therefore, occur under the low temperature conditions of interstellar objects
thus providing a facile formation route of formamide. The rate coefficient
parameters for the reaction channel leading to NH2CHO + H have been calculated
to be A = 2.6x10^{-12} cm^3 s^{-1}, beta = -2.1 and gamma = 26.9 K in the range
of temperatures 10-300 K. Including these new kinetic data in a refined
astrochemical model, we show that the proposed mechanism can well reproduce the
abundances of formamide observed in two very different interstellar objects:
the cold envelope of the Sun-like protostar IRAS16293-2422 and the molecular
shock L1157-B2. Therefore, the major conclusion of this Letter is that there is
no need to invoke grain-surface chemistry to explain the presence of formamide
provided that its precursors, NH2 and H2CO, are available in the gas-phase.Comment: MNRAS Letters, in pres
Quantum chemical computations of gas-phase glycolaldehyde deuteration and constraints to its formation route
Despite the detection of numerous interstellar complex organic molecules
(iCOMs) for decades, it is still a matter of debate whether they are
synthesized in the gas-phase or on the icy surface of interstellar grains. In
the past, molecular deuteration has been used to constrain the formation paths
of small and abundant hydrogenated interstellar species. More recently, the
deuteration degree of formamide, one of the most interesting iCOM, has also
been explained in the hypothesis that it is formed by the gas-phase reaction
NH + HCO. In this article, we aim at using molecular deuteration to
constrain the formation of another iCOM, glycolaldehyde, which is an important
prebiotic species. More specifically, we have performed dedicated electronic
structure and kinetic calculations to establish the glycolaldehyde deuteration
degree in relation to that of ethanol, which is its possible parent species
according to the suggestion of Skouteris et al. (2018). We found that the
abundance ratio of the species containing one D-atom over the all-protium
counterpart depends on the produced D isotopomer and varies from 0.9 to 0.5.
These theoretical predictions compare extremely well with the monodeuterated
isotopomers of glycolaldehyde and that of ethanol measured towards the
Solar-like protostar IRAS 16293-2422, supporting the hypothesis that
glycolaldehyde could be produced in the gas-phase for this source. In addition,
the present work confirms that the deuterium fractionation of iCOMs cannot be
simply anticipated based on the deuterium fractionation of the parent species
but necessitates a specific study, as already shown for the case of formamide.Comment: Accepted by Ap
The census of interstellar complex organic molecules in the Class I hot corino of SVS13-A
We present the first census of the interstellar Complex Organic Molecules
(iCOMs) in the low-mass Class I protostar SVS13-A, obtained by analysing data
from the IRAM-30m Large Project ASAI (Astrochemical Surveys At IRAM). They
consist of an high-sensitivity unbiased spectral survey at the 1mm, 2mm and 3mm
IRAM bands. We detected five iCOMs: acetaldehyde (CHCHO), methyl formate
(HCOOCH), dimethyl ether (CHOCH), ethanol (CHCHOH) and
formamide (NHCHO). In addition we searched for other iCOMs and ketene
(HCCO), formic acid (HCOOH) and methoxy (CHO), whose only ketene was
detected. The numerous detected lines, from 5 to 37 depending on the species,
cover a large upper level energy range, between 15 and 254 K. This allowed us
to carry out a rotational diagram analysis and derive rotational temperatures
between 35 and 110 K, and column densities between and
cm on the 0."3 size previously determined by
interferometric observations of glycolaldehyde. These new observations clearly
demonstrate the presence of a rich chemistry in the hot corino towards SVS13-A.
The measured iCOMs abundances were compared to other Class 0 and I hot corinos,
as well as comets, previously published in the literature. We find evidence
that (i) SVS13-A is as chemically rich as younger Class 0 protostars, and (ii)
the iCOMs relative abundances do not substantially evolve during the
protostellar phase.Comment: 24 pages, MNRAS in pres
Seeds of Life in Space (SOLIS) VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC1333-IRAS4A
Context: Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes.
Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout
the observed outflows.
Aims: The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located
in the Perseus cloud to constrain the physical and chemical processes at work in shocks.
Methods: We observed various transitions from OCS, CS, SO, and SO2 towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands
using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock
model.
Results: The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter
on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by
IRAS4A2 that is extended along the north east–south west direction. SO is detected at extremely high radial velocity up to +25 km s−1
relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated
from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1
and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105
cm−3
and relatively warm (T > 100 K)
temperatures in most cases.
Conclusions: The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar
ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is
more enriched in species that have a gas phase origin, such as SO2
VizieR Online Data Catalog: SOLIS. II. L1157-B1 NH2CHO image (Codella+, 2017)
Datacube in fits format of the NH2CHO(41,4-31,3) towards L1157-B1 using the IRAM-NOEMA interferometer (see Fig. 1). The L1157-B1 shock was observed at 3mm with the IRAM NOEMA seven-element array during several tracks in July, October, and November 2015 using both the C and D configurations. The shortest and longest baselines are 19m and 237m, respectively, allowing us to recover emission at scales up to ~17". (2 data files)
Seeds of Life in Space (SOLIS): VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC 1333-IRAS4A
Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to + 25 km s-1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm-3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2. © ESO 2020.V.T. is grateful to Sylvie Cabrit and Guillaume Pineau des Forêts for stimulating discussions on the chemistry in shocks. The authors acknowledge the CALYPSO consortium for the use of the CALYPSO dataset. This work is based on observations carried out with the IRAM PdBI/NOEMA Interferometer under project numbers V05B and V010 (PI: M.V. Persson), U003 (PI: V. Taquet), and L15AA (PI: C. Ceccarelli and P. Caselli). IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). V.T. acknowledges the financial support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement n. 664931. This work was supported by (i) the PRIN-INAF 2016 “The Cradle of Life – GENESIS-SKA (General Conditions in Early Planetary Systems for the rise of life with SKA)”, (ii) the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme, for the Project “The Dawn of Organic Chemistry” (DOC), grant agreement No 741002, and (iii) the European MARIE SKŁODOWSKA-CURIE ACTIONS under the European Union’s Horizon 2020 research and innovation programme, for the Project “Astro-Chemistry Origins” (ACO), Grant No 811312. C.F. acknowledges support from the French National Research Agency in the framework of the Investissements d’Avenir program (ANR-15-IDEX-02), through the funding of the “Origin of Life” project of the Université Grenoble-Alpes
Vibronic coupling investigation to compute phosphorescence spectra of Pt(II) complexes
The present paper reports a comprehensive quantum mechanical investigation on the luminescence properties of several mono- and dinuclear platinum(II) complexes. The electronic structures and geometric parameters are briefly analyzed together with the absorption bands of all complexes. In all cases agreement with experiment is remarkable. Next, emission (phosphorescence) spectra from the first triplet states have been investigated by comparing different computational approaches and taking into account also vibronic effects. Once again, agreement with experiment is good, especially using unrestricted electronic computations coupled to vibronic contributions. Together with the intrinsic interest of the results, the robustness and generality of the approach open the opportunity for computationally oriented chemists to provide accurate results for the screening of large targets which could be of interest in molecular materials design
Neutral copper(I) complexes featuring phosphinesulfonate chelates
International audienceThe reaction of diphenylphosphinobenzenesulfonic acid with copper(i) oxide resulted in the formation of the new neutral dimeric copper(I) complex {Cu2(DPPBS)2·MeOH)2}. X-ray diffraction studies revealed that the complex has a dimeric structure and a pyramidal trigonal geometry around the copper atom which contains coordinated methanol molecules at the copper centers. Cleavage of the dimer by reaction with various bipyrimidines enabled the preparation of the corresponding well-defined heterotopic mononuclear [Cu(P^O)(N^N)] and dinuclear {(P^O)Cu(N^N)Cu(P^O)} complexes. X-ray crystal structure determination shows these to have distorted tetrahedral geometries. Their absorption and emission properties were investigated experimentally and photophysical data were also confirmed by DFT and TD-DFT calculations. Owing to the methanol molecules, the neutral crystalline dimer {Cu2(DPPBS)2·(MeOH)2} displays green reversible photoluminescence upon UV irradiation in the solid state with an absolute luminescence quantum yield of 0.5