Interstellar Radicals Research Articles

Assessing realistic binding energies of some essential interstellar radicals with amorphous solid water. A fully quantum chemical approach

Assessing realistic binding energies of some essential interstellar radicals with amorphous solid water. A fully quantum chemical approach

Diffuse Bands 9577 and 9633: Relations to Other Interstellar Features

Abstract We study, for the first time, the relations of two strong diffuse bands (DIBs) at 9633 and 9577 Å, commonly attributed to , to other interstellar features seen in optical and UV spectra including H i, Ca i, Fe ii, Na i, Ti ii, CN, CH, CH+, and C2 and DIBs 5780, 5797, 6196, 6269, 6284, and 6614. We analyzed 62 lines of sight where the stellar contamination by Mg ii was corrected or found negligible for DIB 9633. Equivalent widths of DIB 9577 were measured in 62 lines of sight. Poor mutual correlation between the strengths of the above features and the major diffuse bands (5780 and 5797) as well as with other DIBs (with some exceptions) were revealed. The considered DIBs are also poorly correlated with the features of neutral hydrogen, molecular carbon, and those of simple interstellar radicals. Perhaps this phenomenon can be explained if the diffuse band 9577 is an unresolved blend of two or more interstellar features. There are indications that 9633 and 9577 diffuse bands are stronger in σ-type clouds, i.e., these features resemble the behavior of reasonably broad DIBs, which are strong in the lines of sight where the UV flux from the very hot nearby stars plays an important role.

Neural-network assisted study of nitrogen atom dynamics on amorphous solid water – I. adsorption and desorption

ABSTRACT Dynamics of adsorption and desorption of (4S)-N on amorphous solid water are analysed using molecular dynamic simulations. The underlying potential energy surface was provided by machine-learned interatomic potentials. Binding energies confirm the latest available theoretical and experimental results. The nitrogen sticking coefficient is close to unity at dust temperatures of 10 K but decreases at higher temperatures. We estimate a desorption time-scale of 1 μs at 28 K. The estimated time-scale allows chemical processes mediated by diffusion to happen before desorption, even at higher temperatures. We found that the energy dissipation process after a sticking event happens on the picosecond time-scale at dust temperatures of 10 K, even for high energies of the incoming adsorbate. Our approach allows the simulation of large systems for reasonable time-scales at an affordable computational cost and ab initio accuracy. Moreover, it is generally applicable for the study of adsorption dynamics of interstellar radicals on dust surfaces.

Rise of the intensity of interstellar CH+ in the spectrum of AE Aur

AbstractUsing many spectra of the star AE Aur (HD 34078), covering the period 1997–2019, we demonstrate temporal variations of the intensities of spectral features carried by simple interstellar radicals. The drop of the CH+ and CH line intensities was demonstrated by Krełowski et al. (2016)—Paper I. More recent data suggest that the CH+ interstellar lines reach the minimum of intensity in 2015–2016 being then followed by the evident rise, which continues. The intensities of CH lines show a similar drop to CH+. However, the further (after 2016) rise seems marginal if any. Thus, the CH+ features grow since 2016 while those of CH remain almost constant, likely due to the fact that both species are formed in different environments. No variations in the radial velocities of the observed interstellar features were detected during the whole covered time period.

High resolution spectroscopy of jet cooled phenyl radical: The ν1 and ν2 a1 symmetry C-H stretching modes.

A series of CH stretch modes in phenyl radical (C6H5) has been investigated via high resolution infrared spectroscopy at sub-Doppler resolution (∼60 MHz) in a supersonic discharge slit jet expansion. Two fundamental vibrations of a1 symmetry, ν1 and ν2, are observed and rotationally analyzed for the first time, corresponding to in-phase and out-of-phase symmetric CH stretch excitation at the ortho/meta/para and ortho/para C atoms with respect to the radical center. The ν1 and ν2 band origins are determined to be 3073.968 50(8) cm(-1) and 3062.264 80(7) cm(-1), respectively, which both agree within 5 cm(-1) with theoretical anharmonic scaling predictions based on density functional B3LYP/6-311g++(3df,3dp) calculations. Integrated band strengths for each of the CH stretch bands are analyzed, with the relative intensities agreeing remarkably well with theoretical predictions. Frequency comparison with previous low resolution Ar-matrix spectroscopy [A. V. Friderichsen et al., J. Am. Chem. Soc. 123, 1977 (2001)] reveals a nearly uniform Δν ≈ + 10-12 cm(-1) blue shift between gas phase and Ar matrix values for ν1 and ν2. This differs substantially from the much smaller red shift (Δν ≈ - 1 cm(-1)) reported for the ν19 mode, and suggests a simple physical model in terms of vibrational mode symmetry and crowding due to the matrix environment. Finally, the infrared phenyl spectra are well described by a simple asymmetric rigid rotor Hamiltonian and show no evidence for spectral congestion due to intramolecular vibrational coupling, which bodes well for high resolution studies of other ring radicals and polycyclic aromatic hydrocarbons. In summary, the combination of slit jet discharge methods with high resolution infrared lasers enables spectroscopic investigation of even highly reactive combustion and interstellar radical intermediates under gas phase, jet-cooled (Trot ≈ 11 K) conditions.

Antiprotonic helium atomcules

About 3% of antiprotons (p) stopped in helium are long-lived with microsecond lifetimes, against picoseconds in all other materials. This unusual longevity has been ascribed to the trapping of p on metastable bound states in pHe+ helium atom-molecules thus named atomcules. Apart from their unique dual structure investigated by laser spec-troscopy - a near-circular quasi-classical Rydberg atom with l ∼ n - 1 ∼ 37 or a special diatomic molecule with a negatively charged p nucleus in high rotational state with J = l - the chemical physics aspects of their interaction with other atoms or molecules constitute an interesting topic for molecular physics. While atomcules may resist to million collisions in helium, molecular contaminants such as H2 are likely to destroy them in a single one, down to very low temperatures. In the Born-Oppenheimer framework, we interpret the molecular interaction obtained by ab initio quantum chemical calculations in terms of classical reactive channels, with activation barriers accounting for the experiments carried out in He and H2. From classical trajectory Monte Carlo simulations, we show that the thermalization stage strongly quenches initial populations, thus reduced to a recovered 3 % trapping fraction. This work illustrates the pertinence of chemical physics concepts to the study of exotic processes involving antimatter. New insights into the physico-chemistry of cold interstellar radicals are anticipated.

The formation of the stable radicals ˙CH2CN, CH3˙CHCN and ˙CH2CH2CN from the anions−CH2CN, CH3−CHCN and−CH2CH2CN in the gas phase. A joint experimental and theoretical study

Franck-Condon one-electron oxidation of the stable anions -CH2CN, CH3-CHCN and -CH2CH2CN (in the collision cell of a reverse-sector mass spectrometer) produce the radicals .CH2CN, CH3.CHCN and .CH2CH2CN, which neither rearrange nor decompose during the microsecond duration of the neutralisation-reionisation experiment. Acetonitrile (CH3CN) and propionitrile (CH3CH2CN) are known interstellar molecules and radical abstraction of these could produce energised .CH2CN and CH3.CHCN, which might react with NH2. (a known interstellar radical) on interstellar dust or ice surfaces to form NH2CH2CN and NH2CH(CH3)CN, precursors of the amino acids glycine and alanine.

Potential energy surface study of [H, Si, C, N] and its ions

We performed a detailed theoretical study on the neutral, cationic and anionic [H, Si, C, N] potential energy surfaces (PESs) at the Gaussian-3//B3LYP/6-31G(d) level. The former four low-lying isomers HSiCN 11 (0.0 kcal/mol), HSiNC 12 (2.4), cCHNSi 17 (4.6) and HCNSi 13 (28.7) each have considerable kinetic stability, which supports their experimental characterization. In addition, two singlet isomers HNCSi 15 (29.7) and cNHCSi 18 (33.7), and four triplet isomers HSiCN 31 (26.5), HSiNC 32 (35.8), HCNSi 33 (29.1) and HNCSi 35 (29.7) are found to have high kinetic stability. They are expected to be detectable under suitable conditions. On the doublet [H, Si, C, N]+ PES, the linear structure HCNSi+ 23+ (0.0 kcal/mol) and HNCSi+ 25+ (8.6) are considerably more stable than HSiCN+ 21+ (37.2) and HSiNC+ 22+ (34.3), in contrast to the neutral [H, Si, C, N] PES. However, on the doublet anionic [H, Si, C, N]− PES, the isomers HSiCN− 21− (0.0 kcal/mol) and HSiNC− 22− (10.4) are still the lower-lying isomers, similar to the neutral PES. Based on the [H, Si, C, N]0,± PESs, the electron ionization and capture stabilities of various [H, Si, C, N] species are discussed, which might give insight into their mass spectrometric characterization in future. Finally, the proton ionization values of the two known interstellar radicals SiCN and SiNC are found to be very high, showing the high possibility of the existence of the cationic [H, Si, C, N]+ species.

Neutral‐Neutral Reactions in the Interstellar Medium. I. Formation of Carbon Hydride Radicals via Reaction of Carbon Atoms with Unsaturated Hydrocarbons

The reactions of ground-state atomic carbon with acetylene, C2H2 (1), methylacetylene, CH3CCH (2), ethylene, C2H4 (3), and propylene, C3H6 (4), are investigated at relative collision energies between 8.8 and 45 kJ mol-1 in crossed-beam experiments to elucidate the reaction products and chemical dynamics of atom-neutral encounters relevant to the formation of carbon-bearing molecules in the interstellar medium (ISM). Reactive scattering signal is found for C3H (1), as well as the hitherto unobserved interstellar radicals C4H3 (2), C3H3 (3), and C4H5 (4). All reactions proceed on the triplet surface via addition of the carbon atom to the molecular π-bond. The initial collision complexes undergo hydrogen migration (1/2) or ring opening (3/4) and decompose via C-H-bond rupture to l/c-C3H (1), n-C4H3 (2), propargyl (3), and methylpropargyl (4). The explicit identification of the carbon-hydrogen exchange channel under single collision conditions identifies this class of reaction as a potential pathway to carbon-bearing species in the ISM. Especially, the formation of l/c-C3H correlates with actual astronomical observations and explains a higher [c-C3H]/[l-C3H] ratio in the dark cloud TMC-1 as compared to the carbon star IRC +10216. Our findings strongly demand the incorporation of distinct structural isomers in prospective chemical models of interstellar clouds, hot cores, and circumstellar envelopes around carbon stars.

Microwave spectra and electric dipole moments for low-J levels of interstellar radicals: SO, C2S, C3S, c-HC3, CH2CC, and c-C3H2

A number of low-J rotational transitions have been measured for the radical or transient molecular species, SO, C 2 S, C 3 S, c-HC 3 , CH 2 CC, and c-C 3 H 2 . Measurements were made with a pulsed-nozzle, Fabry-Perot cavity, Fourier transform microwave spectrometer equipped with a DC voltage, electric discharge nozzle, Helmholtz coils around the outside of the vacuum chamber were used to maintain the magnetic field within the active volume element of the Fabry-Perot cavity to less than 10 mG

Laboratory millimeter and submillimeter spectrum of CCH

view Abstract Citations (73) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Laboratory millimeter and submillimeter spectrum of CCH Sastry, K. V. L. N. ; Helminger, P. ; Charo, A. ; Herbst, E. ; De Lucia, F. C. Abstract The laboratory millimeter and submillimeter spectrum of the interstellar radical CCH has been observed and measured in the 174-350 GHz region. The fitted spectral constants are in excellent agreement with those determined from radioastronomical measurement. Publication: The Astrophysical Journal Pub Date: December 1981 DOI: 10.1086/183706 Bibcode: 1981ApJ...251L.119S Keywords: Free Radicals; Interstellar Matter; Microwave Spectra; Millimeter Waves; Molecular Spectra; Submillimeter Waves; Astronomical Spectroscopy; Glow Discharges; Microwave Emission; Radio Astronomy; Astrophysics full text sources ADS |

Theoretical studies of interstellar radicals and ions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTheoretical studies of interstellar radicals and ionsStephen WilsonCite this: Chem. Rev. 1980, 80, 3, 263–267Publication Date (Print):June 1, 1980Publication History Published online1 May 2002Published inissue 1 June 1980https://doi.org/10.1021/cr60325a003RIGHTS & PERMISSIONSArticle Views247Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (668 KB) Get e-Alerts Get e-Alerts

Reactions in the Formation of Interstellar Radicals and Molecules

AbstractIn this paper the authors have tried to develop a series of reaction mechanisms which seems to explain the occurrence of the observed interstellar molecules in the dark clouds. Special emphasis is given in this paper to the dominant role of H3+ which acts as a proton donor for the formation of ion molecules like COH+, CH+, NH2+, which are very reactive and lead over a series of intermediates to observed species such as: OH, H2CO, NH3, CH, and HCN. As will be seen, there exists a large variety of possible mechanisms for the formation of certain species and it is premature in many cases to decide which of these mechanisms is dominant. We like to emphasize that the formation of these molecules occurs in the gas phase, a fact which does not exclude the formation of molecules on the surface of grains or in ion‐clusters.

On the detection of microwave spectral lines in radio astronomy.

On the detection of microwave spectral lines in radio astronomy.