Cyano Radical Research Articles

Unsaturated Dinitriles Formation Routes in Extraterrestrial Environments: A Combined Experimental and Theoretical Investigation of the Reaction between Cyano Radicals and Cyanoethene (C2H3CN).

The reaction between cyano radicals (CN, X2Σ+) and cyanoethene (C2H3CN) has been investigated by a combined approach coupling crossed molecular beam (CMB) experiments with mass spectrometric detection and time-of-flight analysis at a collision energy of 44.6 kJ mol–1 and electronic structure calculations to determine the relevant potential energy surface. The experimental results can be interpreted by assuming the occurrence of a dominant reaction pathway leading to the two but-2-enedinitrile (1,2-dicyanothene) isomers (E- and Z-NC–CH=CH–CN) in a H-displacement channel and, to a much minor extent, to 1,1-dicyanoethene, CH2C(CN)2. In order to derive the product branching ratios under the conditions of the CMB experiments and at colder temperatures, including those relevant to Titan and to cold interstellar clouds, we have carried out RRKM statistical calculations using the relevant potential energy surface of the investigated reaction. We have also estimated the rate coefficient at very low temperatures by employing a semiempirical method for the treatment of long-range interactions. The reaction has been found to be barrierless and fast also under the low temperature conditions of cold interstellar clouds and the atmosphere of Titan. Astrophysical implications and comparison with literature data are also presented. On the basis of the present work, 1,2-dicyanothene and 1,1-dicyanothene are excellent candidates for the search of dinitriles in the interstellar medium.

Gas-Phase Preparation of Silyl Cyanide (SiH3CN) via a Radical Substitution Mechanism.

The silyl cyanide (SiH3CN) molecule, the simplest representative of a fully saturated silacyanide, was prepared in the gas phase under single-collision conditions via a radical substitution mechanism. The chemical dynamics were direct and revealed a pronounced backward scattering as a consequence of a transition state with a pentacoordinated silicon atom and almost colinear geometry of the attacking cyano radical and leaving hydrogen. Compared to the isovalent cyano (CN)-methane (CH4) system, the CN-SiH4 system dramatically reduces the energy of the transition state to silyl cyanide by nearly 100 kJ mol-1, which reveals a profound effect on the chemical bonding and reaction mechanism. In extreme high-temperature environments including circumstellar envelopes of IRC +10216, this versatile radical substitution mechanism may synthesize organosilicon molecules via reactions of silane with doublet radicals. Overall, this study provides rare insights into the exotic reaction mechanisms of main-group XIV elements in extreme environments and affords deeper insights into fundamental molecular mass growth processes involving silicon in our universe.

Semiempirical Potential in Kinetics Calculations on the HC3N + CN Reaction.

The reaction between the cyano radical CN and cyanoacetylene molecule HCN is of great interest in different astronomical fields, from star-forming regions to planetary atmospheres. In this work, we present a new synergistic theoretical approach for the derivation of the rate coefficient for gas phase neutral-neutral reactions. Statistic RRKM calculations on the Potential Energy Surface are coupled with a semiempirical analysis of the initial bimolecular interaction. The value of the rate coefficient for the HCN + CN → H + NCCCCN reaction obtained with this method is compared with previous theoretical and experimental investigations, showing strengths and weaknesses of the new presented approach.

Intermolecular interactions of tetracyanoethylene (TCNE) and fumaronitrile (FN) with minor amines: A combined UV-Vis and EPR study.

In this paper, the nature of interactions between two cyanocarbons-tetracyanoethylene (TCNE) and fumaronitrile (FN)-and a series of four secondary amines possessing a general formula C4HxN (x = 5-11) is thoroughly scrutinized. For all of the TCNE-amine pairs, tricyanovinylation (TCV) reaction is observed; however, only for pyrrole, it is accompanied with a visible charge-transfer (CT) complex formation-no such chemical individuals, characteristic for TCNE, have been noticed for aliphatic and alicyclic amines. On the contrary, FN forms such complexes with all the amines studied. Interestingly, a rather unexpected reaction of FN with alicyclic amines has been observed. The recorded electron paramagnetic resonance (EPR) spectra indicate the presence of both TCNE●- and FN●- radicals in the analyzed samples, assigned to a complete charge (electron) transfer process within the CT complexes, whose efficiency can be additionally enhanced by photoirradiation. The origination of the former radical, whose presence is observed also in the TCNE-diethylamine mixture, is as well proposed to result indirectly from the TCV reaction, occurring for this system. Finally, the superhyperfine structure of EPR spectra, indicating the existence of some secondary interactions of the radicals with surrounding compounds, is discussed. Formation of CT complexes and tricyanovinylates has been investigated and characterized with UV-Vis spectroscopy, while the presence of (cyano)radicals in the analyzed mixtures has been evidenced by (photoinduced) EPR measurements. Interpretation of the experimental results is also supplemented with computer simulations including density functional theory calculations.

A numerical methodology based on CFD and plasma chemical kinetics simulations: a focus on the cyano radical

A numerical methodology based on CFD and plasma chemical kinetics simulations: a focus on the cyano radical

Lifetimes and intensities study for the γ and β systems of CN radicals extending to very high vibrational state

The γ (A2Π-X2Σ+) and β (B2Σ+-X2Σ+) systems of cyano (CN) radicals were studied using the highly correlated ab initio approach. The complex behavior of the excited-state wave function calculated at the complete active space self-consistent field (CASSCF) and multireference configuration interaction (MRCI) levels has a great influence on the quality of the transition dipole moment curves (TDMCs). Combining the TDMCs and the Rydberg–Klein–Rees (RKR) potential curves at the MRCI + Q/aV5Z-DK level, the spectroscopic parameters of the higher vibrational bands for the γ (v′ = 0–50 ← v″ = 0–53) and β (v′ = 0–33 ← v″ = 0–53) systems were investigated. The radiation lifetimes of the vibrational levels (v′ = 0–15) were obtained. A list of wavelengths and Einstein A coefficients of the lower vibrational bands (v′ = 0–2 ← v'' = 0–2) is provided and compared with other results. The spectral intensities of the γ system 2–0 band and the β system 0–0 band at different temperatures (300, 5000, and 10,000 K) are discussed. As the temperature increases, the bandwidths become broader, and the intensities decrease. These results are relevant for the applications in astrophysics and chemistry, especially in space vehicles.

Cyanide removal from aqueous environment by resting cells and PTFE immobilized cells of Sphingobacterium spp.

Microbial detoxification of cyanide offered an inexpensive, safe, and viable alternative to physiochemical processes for the treatment of cyanide in industrial effluents or contaminated sites. This study involved isolation of novel strain with high resistance against cyanide toxicity and able to degrade the cyanide radical. The strain was isolated from rocky area and identified as Sphingobacterium multivorium using 16S ribosomal RNA. Resting pregrown cells were used in simple reaction mixture to avoid the complication associated with the media. One-gram fresh weight of this bacteria was able to remove 98.5% from 1.5 g/L cyanide which is a unique result. Factor affecting the biochemical process such as pH, temperature, agitation, glucose concentration was examined. The optimum conditions were, pH 6-7, 30-40°C, and 100-150 rpm shaking speed and 0.25% glucose. Furthermore, the cells were used after immobilization in polytetrafluoroethylene (PTFE) polymer. The PTFE is very safe carrier and the cells withstand the entrapment process and were able to remove 92% (1 g/L cyanide). The immobilized cells were used for six successive cycles with about 50% removal efficiency. The storage life extended to 14 days. No previous work studied the cyanide removal by Sphingobacterium spp. The strain showed good applicable characters.

Mineralization of cyanides via a novel Electro-Fenton system generating •OH and •O2−

Traditional methods of cyanides’ (CN−) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO−) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2−. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2− were simultaneously generated and 92.9% of free cyanides were transformed into NO3- within 120 min. No low-toxic CNO− intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN− was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2− via nucleophilic addition to quickly form NO3-, preventing the formation of CNO− and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.

Discovery of two isomers of ethynyl cyclopentadiene in TMC-1: Abundances of CCH and CN derivatives of hydrocarbon cycles

We report the detection of two isomers of ethynyl cyclopentadiene (c-C5H5CCH), namely 1- and 2-ethynyl-1,3-cyclopentadiene, in the direction of TMC-1. We derive column densities of (1.4 ± 0.2) × 1012 cm−2 and (2.0 ± 0.4) × 1012 cm−2, respectively, for these two cyclopentadiene derivatives, which imply that they are about ten times less abundant than cyclopentadiene. We also report the tentative detection of ethynyl benzene (C6H5CCH), for which we estimate a column density of (2.5 ± 0.4) × 1012 cm−2. We derived abundances for the corresponding cyano derivatives of cyclopentadiene and benzene and found values significantly lower than previously reported. The rotational temperature of the ethynyl and cyano derivatives of these cycles is about 9 K, that is, very close to the gas kinetic temperature of the cloud. The abundance ratio of the 1- and 2-isomers of ethynyl cyclopentadiene is 1.4 ± 0.5, while for the two isomers of cyano cyclopentadiene it is 2.4 ± 0.6. The relative abundances of CCH over CN derivatives is 7.7 ± 2.2 for cyclopentadiene, which probably reflects the abundance ratio of the radicals CCH and CN; this ratio is only 2.1 ± 0.5 for benzene, which suggests that additional reactions besides cyano radicals with benzene are involved in the formation of benzonitrile. The formation of these cycles is reasonably well accounted for through a chemical scheme based on neutral-neutral reactions. It is predicted that benzene should be as abundant as cyclopentadiene in TMC-1.

Air–Carbon Ablation Model for Hypersonic Flight from Molecular-Beam Data

Recent molecular-beam experiments of high-velocity atomic oxygen (O), atomic nitrogen (N), and molecular oxygen () impacting carbon material at high temperature produced detailed surface chemistry data relevant for carbon ablation processes. New data on O and N reactions with carbon have been published using a continuous molecular beam with lower velocity () and approximately 500-times-higher beam flux than previous pulsed-beam experiments. These data are interpreted to construct a new air–carbon ablation model for use in modeling carbon heat shield ablation. The new model comprises 20 reaction mechanisms describing reactions between impinging O, N, and species with carbon and producing scattered products including desorbed O and N; and molecular nitrogen () formed by surface-catalyzed recombination; as well as carbon monoxide (CO), carbon dioxide (), and cyano radical (CN). The new model includes surface-coverage-dependent reactions and exhibits a non-Arrhenius reaction probability in agreement with experimental observations. All reaction mechanisms and rate coefficients are described in detail, and each is supported by experimental evidence or theory. The model predicts pressure effects and is tested for a wide range of temperatures and pressures relevant to hypersonic flight. Model results are shown to agree well with available data and are shown to have significant differences as compared to other models from the literature.

Cyano radical emission at small spatial scales towards massive protostars

Context. The cyano radical (CN), one of the first detected interstellar molecular species, is a key molecule in many astrochemical chains. In particular, it is detected towards molecular cores, the birth places of stars, and it is involved in the rich chemistry that takes place at these sites. Aims. At present, there are not many studies on the emission of this molecular species at small spatial scales towards massive young stellar objects. We therefore present a high-angular resolution CN study towards a sample of massive protostars, with the aim of unveiling the spatial distribution at the small scale of the emission of this radical in relation to star-forming processes. Methods. The interstellar CN has a strong emission line at the rest frequency 226 874.764 MHz, thus we searched for observing projects in the Atacama Large Millimeter Array (ALMA) database regarding high-mass star-forming regions observed at Band 6. The used data set was observed in ALMA Cycle 3 with angular and spectral resolutions of 0.′′7 and 1.13 MHz, respectively. A sample of ten high-mass star-forming regions located in the first Galactic quadrant were selected on the basis that they present a clear emission of CN at the mentioned frequency. Results. We found that the CN traces both molecular condensations and the diffuse and extended gas surrounding them. In general, the molecular condensations traced by the maximums of the CN emission do not spatially coincide with the peaks of the continuum emission at 1.3 mm, which trace the molecular cores where massive stars are born. Based on the presence or lack of near-IR emission associated with such cores, we suggest that our sample is composed of sources at different stages of evolution. The CN is present in all sources, suggesting that this radical may be ubiquitous along the different star formation stages, and hence it may be involved in different chemical reactions occurring during the period of star formation. Additionally, other molecules such as CH3OCHO and CH2CHCN were detected towards the continuum peaks of some of the analysed cores. We found that the missing flux coming from extended spatial scales that are filtered out by the interferometer is an important issue to take into account in the analysis of some spectral features and the spatial distribution of the emission.

High‐Speed Spectroscopy of Lightning‐Like Discharges: Evidence of Molecular Optical Emissions

AbstractHigh speed spectra (between ∼380 nm and ∼800 nm) of meter‐long lightning‐like discharges recorded at 672,000 fps and 1,400,000 fps (with 1.488 and 0.714 μs time resolutions and 160 ns exposure time) show optical emissions of neutral hydrogen, singly ionized nitrogen, oxygen, and doubly ionized nitrogen which are similar to those found in natural lightning optical emissions. The spectra recorded in the near ultraviolet‐blue range (380–450 nm) and visible‐near infrared (475–793 nm) exhibited features of optical emissions corresponding to several molecular species (and emission bands) like cyanide radical (CN) (Violet bands), N2 (Second Positive System), N2+ (first negative system), C2 (Swan band) and CO (Quintet and Ångström bands). Molecular species can be formed at regions of the lightning‐like channel where the gas temperature would be milder and/or in the corona sheath surrounding the heated channel. We have quantified and compared electron densities and temperatures derived from different sets of neutral and ion line emissions and have found different sensitivities depending on the lines used. Temperatures derived from ion emissions are higher and change faster than those derived from neutral emissions.

Cyanogen, cyanoacetylene, and acetonitrile in comet 67P and their relation to the cyano radical

The cyano radical (CN) is one of the most frequently remotely observed species in space, and is also often observed in comets. Data for the inner coma of comet 67P/Churyumov-Gerasimenko collected by the high-resolution Double Focusing Mass Spectrometer (DFMS) on board the Rosetta orbiter revealed an unexpected chemical complexity, and, recently, also more CN than expected from photodissociation of its most likely parent, hydrogen cyanide (HCN). Here, we derive abundances relative to HCN of three cometary nitriles (including structural isomers) from DFMS data. Mass spectrometry of complex mixtures does not always allow isolation of structural isomers, and therefore in our analysis we assume the most stable and abundant (in similar environments) structure, that is HCN for CHN, CH3CN for C2H3N, HC3N for C3HN, and NCCN for C2N2. For cyanoacetylene (HC3N) and acetonitrile (CH3CN), the complete mission time-line was evaluated, while cyanogen (NCCN) was often below the detection limit. By carefully selecting periods where cyanogen was above the detection limit, we were able to follow the abundance ratio between NCCN and HCN from 3.16 au inbound to 3.42 au outbound. These are the first measurements of NCCN in a comet. We find that neither NCCN nor either of the other two nitriles is sufficiently abundant to be a relevant alternative parent to CN.

Energetics and kinetics of various cyano radical hydrogen abstractions.

The cyano radical (CN) is an abundant, open-shell molecule found in a variety of environments, including the atmosphere, the interstellar medium and combustion processes. In these environments, it often reacts with small, closed-shell molecules via hydrogen abstraction. Both carbon and nitrogen atoms of the cyano radical are reactive sites, however the carbon is more reactive with reaction barrier heights generally between 2-15 kcal mol-1 lower than those of the analogous nitrogen. The CN + HX → HCN/HNC + X, with X = H, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, C2H, CN reactions have been studied at a high-level of theory, including CCSD(T)-F12a. Furthermore, kinetics were obtained over the 100-1000 K temperature range, showing excellent agreement with those rate constants that have been determined experimentally.

Quantum chemical study on the formation of isopropyl cyanide and its linear isomer in the interstellar medium

AbstractThe formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

Experimental energy levels of 12C14N through marvel analysis.

The cyano radical (CN) is a key molecule across many different factions of astronomy and chemistry. Accurate, empirical rovibronic energy levels with uncertainties are determined for eight doublet states of CN using the marvel (Measured Active Rotational-Vibrational Energy Levels) algorithm. 40 333 transitions were validated from 22 different published sources to generate 8083 spin-rovibronic energy levels. The empirical energy levels obtained from the marvel analysis are compared to current energy levels from the mollist line list. The mollist transition frequencies are updated with marvel energy level data which brings the frequencies obtained through experimental data up to 77.3percent from the original 11.3percent, with 92.6percent of the transitions with intensities over 10-23 cm molecule-1 at 1000K now known from experimental data. At 2000K, 100.0percent of the partition function is recovered using only marvel energy levels, while 98.2percent is still recovered at 5000K.

First in situ detection of the CN radical in comets and evidence for a distributed source

ABSTRACT Although the debate regarding the origin of the cyano (CN) radical in comets has been ongoing for many decades, it has yielded no definitive answer to date. CN could previously only be studied remotely, strongly hampering efforts to constrain its origin because of very limited spatial information. Thanks to the European Space Agency's Rosetta spacecraft, which orbited comet 67P/Churyumov–Gerasimenko for 2 yr, we can investigate, for the first time, CN around a comet at high spatial and temporal resolution. On board Rosetta's orbiter module, the high-resolution double-focusing mass spectrometer DFMS, part of the ROSINA instrument suite, analysed the neutral volatiles (including HCN and the CN radical) in the inner coma of the comet throughout that whole 2-yr phase and at variable cometocentric distances. From a thorough analysis of the full-mission data, the abundance of CN radicals in the cometary coma has been derived. Data from a close flyby event in 2015 February indicate a distributed origin for the CN radical in comet 67P/Churyumov–Gerasimenko.

The Quest for a Plausible Formation Route of Formyl Cyanide in the Interstellar Medium: a State-of-the-art Quantum-chemical and Kinetic Approach

Abstract Interstellar complex organic molecules are assumed to be mainly formed on dust–grain surfaces. However, neutral gas-phase reactions in the interstellar medium can play an important role. In this paper, by investigating the reaction between aldehydes and the cyano radical, we show that both formaldehyde (CH2O) and acetaldehyde (CH3CHO) can lead to the formation of formyl cyanide (HCOCN). Owing to accurate quantum-chemical computations followed by rate constant evaluations, we have been able to suggest and validate an effective mechanism for the formation of HCOCN, one of the molecules observed in the ISM. Quite interestingly, the mechanism starting from CH2O is very effective at a low temperature, while that involving CH3CHO becomes more efficient at temperatures above 200 K.

A twist on the reaction of the CN radical with methylamine in the interstellar medium: new hints from a state-of-the-art quantum-chemical study

ABSTRACTDespite the fact that the majority of current models assume that interstellar complex organic molecules (iCOMs) are formed on dust–grain surfaces, there is some evidence that neutral gas-phase reactions play an important role. In this paper, we investigate the reaction occurring in the gas phase between methylamine (CH3NH2) and the cyano (CN) radical, for which only fragmentary and/or inaccurate results have been reported to date. This case study allows us to point out the pivotal importance of employing quantum-chemical calculations at the state of the art. Since the two major products of the CH3NH2 + CN reaction, namely the CH3NH and CH2NH2 radicals, have not been spectroscopically characterized yet, some effort has been made for filling this gap.

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV-Vis Spectroscopic Study of the Violet Emission of CN Radical.

Exploring the formation of diatomic radicals in femtosecond plasmas is important to establish the most dominant kinetic pathways following ionization and dissociation of small molecules. In this work, cyano radical formation has been studied from bromoform, acetonitrile, and methanol in nitrogen and argon plasmas created with a focused femtosecond laser beam operating at 100 kHz repetition rate and 1030 nm wavelength with 43 fs pulse length and 250 μJ pulse energy. Time-resolved Fourier transform fluorescence spectroscopy was applied in the ultraviolet-visible (UV-vis) spectral range for the characterization of the rotational and vibrational temperatures of the CN(B) radicals via fitting the experimental data. The high repetition rate of the laser allows efficient coupling with the step-scan Fourier transform spectroscopy method. Coulomb explosion at the very high intensity (∼1016 W/cm2) resulted in the formation of nascent atoms, ions, and electrons. The condensation reactions of carbon and reactive nitrogen species resulted in the formation of CN(B2Σ+) radicals and C2(d3Πg) dicarbon molecules/radicals. The CN(B) radicals were formed at the highest concentration in the case of bromoform because the weak carbon-bromine bonds resulted in reactive carbon atoms and CH radicals, which are reactive precursors for the CN(B) radical formation. In the case of acetonitrile, immediate production of CN(B) is observed with nanosecond resolution, which suggests that the CN is formed either via photodetachment or via roaming reaction associated with the Coulomb explosion of the parent molecule. The nascent rotational temperature was very high (∼6000-8500 K) and rapidly decreased in all instances within 40 ns with bromoform and acetonitrile. The highest vibrational temperature (∼7800 K) was observed in an acetonitrile/Ar mixture that decreased in about 30 ns and then increased in the observed time window. The vibrational temperature increased in all samples between 30 and 200 ns. The time dependence of fluorescence is described with a monoexponential decay in the case of acetonitrile/Ar and with biexponential decays in all other instances in the 0-250 mbar total pressure range. The shorter time constant is close to the radiative lifetime of CN(B) emission (∼60-80 ns), which can be attributed to the CN(B) radicals produced in the first few collisions at lower pressures. The longer CN(B) emission is from CN(B) created by slower chemical reactions involving carbon atoms, C2 radicals, and reactive nitrogen-containing species.