Neutral Reaction Products Research Articles

An efficient synthesis of some new bipyrazole derivatives by three-component reaction between 3-methyl-1H-pyrazol-4(5H)-one, aroylphenylhydrazones and arylglyoxals

A simple one-pot and catalyst-free method is reported for synthesis of some new bipyrazole derivatives by three-component reaction between arylglyoxals, 3-methyl-1H-pyrazol-4(5H)-one and aroylphenylhydrazone derivatives. The reactions were carried out in ethanol as a green solvent in neutral reaction conditions and products were simply isolated by filtering of the precipitated solids in high yields. All products were characterized by their 1H and 13C NMR and IR spectral and elemental analysis data.

Near-thermo-neutral electron recombination of titanium oxide ions.

While the dissociative recombination (DR) of ground-state molecular ions with low-energy free electrons is generally known to be exothermic, it has been predicted to be endothermic for a class of transition-metal oxide ions. To understand this unusual case, the electron recombination of titanium oxide ions (TiO+) with electrons has been experimentally investigated using the Cryogenic Storage Ring. In its low radiation field, the TiO+ ions relax internally to low rotational excitation (≲100 K). Under controlled collision energies down to ∼2 meV within the merged electron and ion beam configuration, fragment imaging has been applied to determine the kinetic energy released to Ti and O neutral reaction products. Detailed analysis of the fragment imaging data considering the reactant and product excitation channels reveals an endothermicity for the TiO+ dissociative electron recombination of (+4 ± 10) meV. This result improves the accuracy of the energy balance by a factor of 7 compared to that found indirectly from hitherto known molecular properties. Conversely, the present endothermicity yields improved dissociation energy values for D0(TiO) = (6.824 ± 0.010)eV and D0(TiO+) = (6.832 ± 0.010)eV. All thermochemistry values were compared to new coupled-cluster calculations and found to be in good agreement. Moreover, absolute rate coefficients for the electron recombination of rotationally relaxed ions have been measured, yielding an upper limit of 1 × 10-7 cm3 s-1 for typical conditions of cold astrophysical media. Strong variation of the DR rate with the TiO+ internal excitation is predicted. Furthermore, potential energy curves for TiO+ and TiO have been calculated using a multi-reference configuration interaction method to constrain quantum-dynamical paths driving the observed TiO+ electron recombination.

Association Reaction of Gaseous C2H4 in Femtosecond Laser Filaments Studied by Time-of-Flight Mass Spectrometry.

Association reactions by femtosecond laser filamentation in gaseous C2H4 were studied by time-of-flight mass spectrometry of neutral reaction products. Direct sampling from the reaction cell to a mass spectrometer via a differential pumping stage allowed the identification of various hydrocarbon molecules CnHm with n = 3–7 and m = 4–7, which includes species not observed in the previous studies. It was found that products containing three and four carbon atoms dominate the mass spectrum with smaller yields for higher-mass species, suggesting that carbon chain growth proceeds through the reaction with C2H4 in the reaction cell. The product distribution showed a clear dependence on the laser pulse energy for filamentation.

A Photoionization Study on the Detection of 1-Sila Glycolaldehyde (HSiOCH2 OH), 2-Sila Acetic Acid (H3 SiCOOH), and 1,2-Disila Acetaldehyde (HSiOSiH3 ).

The identification of silicon-substituted, complex organics carrying multiple functional groups by classical infrared spectroscopy is challenging because the group frequencies of functional groups often overlap. Photoionization (PI) reflectron time-of-fight mass spectrometry (ReTOF-MS) in combination with temperature-programmed desorption (TPD) holds certain advantages because molecules are identified after sublimation from the matrix into in the gas phase based on distinct ionization energies and sublimation temperatures. In this study, we reveal the detection of 1-silaglycolaldehyde (HSiOCH2 OH), 2-sila-acetic acid (H3 SiCOOH), and 1,2-disila-acetaldehyde (H3 SiSiHO)-the silicon analogues of the well-known glycolaldehyde (HCOCH2 OH), acetic acid (H3 CCOOH), and acetaldehyde (H3 CCHO), in the gas phase after preparation in silane (SiH4 )-carbon dioxide ices exposed to energetic electrons and subliming the neutral reaction products formed within the ices into the gas phase.

Interstellar Formation of Biorelevant Pyruvic Acid (CH <sub>3</sub>COCOOH)

Pyruvic acid represents a key molecular building block in prebiotic chemistry to form metabolites and amino acids. As conditions on early Earth were not favorable for an endogenous formation of pyruvic acid, an exogenous delivery by comets and meteorites constitutes an appealing alternative. However, despite the detection of more than 200 molecules in interstellar and circumstellar environments, pyruvic acid has yet remained elusive. Here we report on the formation of pyruvic acid by barrierless recombination of hydroxycarbonyl (HOCO) and acetyl (CH3CO) radicals in interstellar ices modelling interstellar conditions of acetaldehyde (CH3CHO) and carbon dioxide (CO2) driven by galactic cosmic rays. Exploiting isotopically labelled ices and photoionization reflectron time-of-flight mass spectrometry, the subliming neutral reaction products were selectively photoionized in the temperature programmed desorption phase and isomers discriminated based on their distinct ionization energies. These results reveal a key reaction pathway for the synthesis of pyruvic acid through non-equilibrium reactions in interstellar ices in cold molecular clouds like TMC-1 and star forming regions such as the Orion Molecular Cloud complex (OMC-1), thus offering a unique entry point to abiotic organic synthesis in deep space.

Impact of hexamethyldisiloxane admixtures on the discharge characteristics of a dielectric barrier discharge in argon for thin film deposition

Atmospheric‐pressure dielectric barrier discharges (DBDs) in argon with admixtures of small amounts of hexamethyldisiloxane (HMDSO) have been analysed by means of numerical modelling. A time‐dependent, spatially one‐dimensional fluid‐Poisson model has been used, which takes into account the spatial variation of the discharge plasma between the plane‐parallel dielectrics covering the electrodes. Main features of the model, including the reaction kinetics for HMDSO, are given. Good agreement with related experimental studies of the ignition voltage for HMDSO amounts of up to 200 ppm and the temporal course of the discharge current for conditions typical of deposition experiments is obtained by the model calculations when assuming that 30% of the reactions of HMDSO with excited argon atoms, with a rate coefficient of 5.0 × 10−10 cm3/s, lead to the production of electrons due to Penning ionization. The modelling results for constant frequency f = 86.2 kHz and applied voltage Ua = 4 kV show that the electrical energy dissipated in the DBD decreases with an increasing amount of HMDSO and enable the determination of the energy absorbed per HMDSO molecule on the basis of their energy balance. The analysis of the plasma–chemical processes also makes clear that collision processes of HMDSO with excited argon atoms and molecules leading to neutral reaction products are essential for the formation of thin polymer films.

The study of cesium ionization at high gas temperature in a primary circuit

A kinetic model has been presented in developing a better understanding of the mechanism behind the ions formation at high gas temperature in a primary circuit in conditions of severe accidents. The formation of ions is triggered by the thermal ionization of cesium atoms and irradiation of a hot steam. The kinetics of ions is considered in combination with the neutral chemistry of cesium and iodine species. Modeling results are presented for temperatures 2000 and 1200K and a dose rate of 1000kGy/s. The evolution of the concentrations of the most abundant ions and neutral reaction products are calculated.

Electrons Mediate the Gas‐Phase Oxidation of Formic Acid with Ozone

Gas-phase reactions of CO3 (.-) with formic acid are studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Signal loss indicates the release of a free electron, with the formation of neutral reaction products. This is corroborated by adding traces of SF6 to the reaction gas, which scavenges 38 % of the electrons. Quantum chemical calculations of the reaction potential energy surface provide a reaction path for the formation of neutral carbon dioxide and water as the thermochemically favored products. From the literature, it is known that free electrons in the troposphere attach to O2 , which in turn transfer the electron to O3 . O3 (.-) reacts with CO2 to form CO3 (.-) . The reaction reported here formally closes the catalytic cycle for the oxidation of formic acid with ozone, catalyzed by free electrons.

Modelling of catalytically oxidative decomposition of carbon tetrachloride on a ZnS nanocluster using density functional theory

Using density functional theory (DFT), adsorption of O2 and co-adsorption of O2 and CCl4 on (ZnS)n clusters (n = 6, 7, 11, 12, 13, 15, 16, 17, 25, 26) and the mechanism of oxidative decomposition of CCl4 on a ZnS nanocluster were investigated. The decomposition of CCl4 without the ZnS cluster was also studied for comparison. The ZnS cluster achieved a significant catalytic effect during the oxidative decomposition of CCl4. It is found that CCl4 in gas phase undergoes a homolytic dissociation process with the activation by ZnS, reacting with O2 to produce a CCl3˙ radical and a ClOO˙ radical first. CO2 and Cl2 are identified as the final neutral reaction products, while COCl2, CO and Cl2O are produced as intermediates. The released energy of the total reaction, 149.83 kcal mol−1, is sufficient to afford the transition energy of the cataluminescence, based on which a novel and sensitive gas sensor for the determination of CCl4 could be constructed.

On the role of thermal activation in selective photochemistry: mechanistic insight into the oxidation of propene on the V4O11−cluster

An experimental methodology for a mechanistic analysis of gas phase chemical reactions is presented in the context of structure-reactivity relationships of metal oxide clusters relevant to photocatalysis. The spectroscopic approach is demonstrated with the investigation of the photoinduced oxygenation of propene on the V(4)O(11)(-) cluster, where the thermal activation and subsequent photoreaction are deduced with the information from (i) the temperature dependency of the aggregation kinetics in the propene-seeded helium atmosphere of an ion-trap reactor; (ii) the fluence dependency in the yield of different product channels of the photoreaction and (iii) the intensity dependency in the fragmentation of neutral reaction products that are probed via in situ multi-photon ionization. For the thermal reaction, selective hydrogen abstraction from the allylic position of propene accompanied by the linkage to the cluster at the dioxo moiety is postulated as the mechanism in the aggregation of propene on the V(4)O(11)(-) cluster. In accordance with an insightful neutralization-reionization study (Schröder et al., J. Mass. Spectrom., 2010, 301, 84), the subsequent photoinduced reaction is defined by an allylic oxidation in the formation of acrolein from the initial allyloxy radical photoproduct. The relevance of the observed selectivity is discussed in view of the electronic structure and bond motifs offered by high valence oxide systems such as the V(4)O(11)(-) cluster.

Experimental and theoretical studies of reactions of neutral vanadium and tantalum oxide clusters with NO and NH3

Reactions of neutral vanadium and tantalum oxide clusters with NO, NH(3), and an NO/NH(3) mixture in a fast flow reactor are investigated by time of flight mass spectrometry and density functional theory (DFT) calculations. Single photon ionization through a 46.9 nm (26.5 eV) extreme ultraviolet (EUV) laser is employed to detect both neutral cluster distributions and reaction products. Association products VO(3)NO and V(2)O(5)NO are detected for V(m)O(n) clusters reacting with pure NO, and reaction products, TaO(3,4)(NO)(1,2), Ta(2)O(5)NO, Ta(2)O(6)(NO)(1-3), and Ta(3)O(8)(NO)(1,2) are generated for Ta(m)O(n) clusters reacting with NO. In both instances, oxygen-rich clusters are the active metal oxide species for the reaction M(m)O(n)+NO→M(m)O(n)(NO)(x). Both V(m)O(n) and Ta(m)O(n) cluster systems are very active with NH(3). The main products of the reactions with NH(3) result from the adsorption of one or two NH(3) molecules on the respective clusters. A gas mixture of NO:NH(3) (9:1) is also added into the fast flow reactor: the V(m)O(n) cluster system forms stable, observable clusters with only NH(3) and no V(m)O(n)(NO)(x)(NH(3))(y) species are detected; the Ta(m)O(n) cluster system forms stable, observable mixed clusters, Ta(m)O(n)(NO)(x)(NH(3))(y), as well as Ta(m)O(n)(NO)(x) and Ta(m)O(n)(NH(3))(y) individual clusters, under similar conditions. The mechanisms for the reactions of neutral V(m)O(n) and Ta(m)O(n) clusters with NO/NH(3) are explored via DFT calculations. Ta(m)O(n) clusters form stable complexes based on the coadsorption of NO and NH(3). V(m)O(n) clusters form weakly bound complexes following the reaction pathway toward end products N(2)+H(2)O without barrier. The calculations give an interpretation of the experimental data that is consistent with the condensed phase reactivity of V(m)O(n) catalyst and suggest the formation of intermediates in the catalytic chemistry.

Investigation of the reactions of small neutral iron oxide clusters with methanol

Reactions of neutral iron oxide clusters (Fe(m)O(n), m=1-2, n=0-5) with methanol (CH(3)OH) in a fast flow reactor are investigated by time of flight mass spectrometry. Detection of the neutral iron oxide cluster distribution and reaction intermediates and products is accomplished through single photon ionization by a 118 nm (10.5 eV) VUV laser. Partially deuterated methanol (CD(3)OH) is employed to distinguish reaction products and reaction mechanisms. Three major reactions are identified experimentally: CH(3)OH association with FeO; methanol dehydrogenation on FeO(1,2) and Fe(2)O(2-5); and (CH(2)O)Fe formation. Density functional theory calculations are carried out to identify reaction products, and to explore the geometric and electronic structures of the iron oxide clusters, reaction intermediates, and transition states, and to evaluate reaction pathways. Neutral formaldehyde is calculated to be formed on FeO(1,2) and Fe(2)O(2-5) clusters. Hydrogen transfer from methanol to iron oxide clusters occurs first from the O-H moiety of methanol, and is followed by a hydrogen transfer from the C-H moiety of methanol. Computational results are in good agreement with experimental observations and reveal reaction mechanisms for neutral iron oxide clusters taking methanol to formaldehyde through various reaction intermediates. Based on the experimental results and the calculated reaction mechanisms and pathways, complete catalytic cycles are suggested for the heterogeneous reaction of CH(3)OH to CH(2)O facilitated by an iron oxide catalyst.

Reactions of Neutral Vanadium Oxide Clusters with Methanol

Reactions of neutral vanadium oxide clusters with methanol and ethanol in a fast-flow reactor are investigated by time-of-flight mass spectrometry. Single-photon ionization through soft X-ray (46.9 nm, 26.5 eV) and vacuum ultraviolet (VUV, 118 nm, 10.5 eV) lasers is employed to detect both neutral cluster distributions and reaction products. In order to distinguish isomeric products generated in the reactions V(m)O(n) + CH(3)OH, partially deuterated methanol (CD(3)OH) is also used as a reactant in the experiments. Association products are observed for most vanadium oxide clusters in reaction with methanol. Products VOD, V(2)O(3)D, V(3)O(6)D, and V(4)O(9)D are observed for oxygen-deficient vanadium oxide clusters reacting with methanol, while oxygen-rich and the most stable clusters can extract more than one hydrogen atom (H/D) from CD(3)OH to form products VO(2)DH(0,1), V(2)O(4)DH(0,1), V(2)O(5)DH(0,1), V(3)O(7)DH(0,1), and V(4)O(10)DH(0,1). Species VO(2)(CH(3))(2), VO(3)(CH(3))(2), V(2)O(5)(CH(3))(2), V(3)O(7)(CH(3))(2), and V(3)O(8)(CH(3))(2) are identified as some of the main products generated from a dehydration reaction for V(m)O(n) + CH(3)OH. A minor reaction channel that generates VOCH(2)O (VOCD(2)O) and VO(2)CH(2)O (VO(2)CD(2)O) can also be identified. An obviously different behavior appears in the reaction V(m)O(n) + C(2)H(5)OH. The main observed products for this reaction are association products of the form V(m)O(n)C(2)H(5)OH. In order to explore the mechanism of V(m)O(n) + CH(3)OH reactions, DFT calculations are performed to study the reaction pathways of VO(2) + CH(3)OH and VO + CH(3)OH reaction systems. The calculation results are in good agreement with the experimental observations.

C═C Bond Cleavage on Neutral VO3(V2O5)n Clusters

The reactions of neutral vanadium oxide clusters with alkenes (ethylene, propylene, 1-butene, and 1,3-butadiene) are investigated by experiments and density function theory (DFT) calculations. Single photon ionization through extreme ultraviolet radiation (EUV, 46.9 nm, 26.5 eV) is used to detect neutral cluster distributions and reaction products. In the experiments, we observe products (V(2)O(5))(n)VO(2)CH(2), (V(2)O(5))(n)VO(2)C(2)H(4), (V(2)O(5))(n)VO(2)C(3)H(4), and (V(2)O(5))(n)VO(2)C(3)H(6), for neural V(m)O(n) clusters in reactions with C(2)H(4), C(3)H(6), C(4)H(6), and C(4)H(8), respectively. The observation of these products indicates that the C=C bonds of alkenes can be broken on neutral oxygen rich vanadium oxide clusters with the general structure VO(3)(V(2)O(5))(n=0,1,2...). DFT calculations demonstrate that the reaction VO(3) + C(3)H(6) --> VO(2)C(2)H(4) + H(2)CO is thermodynamically favorable and overall barrierless at room temperature. They also provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes is broken on VO(3)(V(2)O(5))(n=0,1,2...) clusters. A catalytic cycle for alkene oxidation on vanadium oxide is suggested based on our experimental and theoretical investigations. The reactions of V(m)O(n) with C(6)H(6) and C(2)F(4) are also investigated by experiments. The products VO(2)(V(2)O(5))(n)C(6)H(4) are observed for dehydration reactions between V(m)O(n) clusters and C(6)H(6). No product is detected for V(m)O(n) clusters reacting with C(2)F(4). The mechanisms of the reactions between VO(3) and C(2)F(4)/C(6)H(6) are also investigated by calculations at the B3LYP/TZVP level.

Experimental and Theoretical Study of the Reactions between Neutral Vanadium Oxide Clusters and Ethane, Ethylene, and Acetylene

Reactions of neutral vanadium oxide clusters with small hydrocarbons, namely C2H6, C2H4, and C2H2, are investigated by experiment and density functional theory (DFT) calculations. Single photon ionization through extreme ultraviolet (EUV, 46.9 nm, 26.5 eV) and vacuum ultraviolet (VUV, 118 nm, 10.5 eV) lasers is used to detect neutral cluster distributions and reaction products. The most stable vanadium oxide clusters VO2, V2O5, V3O7, V4O10, etc. tend to associate with C2H4 generating products V(m)O(n)C2H4. Oxygen-rich clusters VO3(V2O5)(n=0,1,2...), (e.g., VO3, V3O8, and V5O13) react with C2H4 molecules to cause a cleavage of the C=C bond of C2H4 to produce (V2O5)(n)VO2CH2 clusters. For the reactions of vanadium oxide clusters (V(m)O(n)) with C2H2 molecules, V(m)O(n)C2H2 are assigned as the major products of the association reactions. Additionally, a dehydration reaction for VO3 + C2H2 to produce VO2C2 is also identified. C2H6 molecules are quite stable toward reaction with neutral vanadium oxide clusters. Density functional theory calculations are employed to investigate association reactions for V2O5 + C2H(x). The observed relative reactivity of C2 hydrocarbons toward neutral vanadium oxide clusters is well interpreted by using the DFT calculated binding energies. DFT calculations of the pathways for VO3+C2H4 and VO3+C2H2 reaction systems indicate that the reactions VO3+C2H4 --> VO2CH2 + H2CO and VO3+C2H2 --> VO2C2 + H2O are thermodynamically favorable and overall barrierless at room temperature, in good agreement with the experimental observations.

Toward Actinide Molecular Magnetic Materials: Coordination Polymers of U(IV) and the Organic Acceptors TCNQ and TCNE

Molecular materials of transition metal ions and organic acceptors of the general formula M(TCNX)2 M=V, Mn, Fe, Co, Ni; X=Q=7,7,8,8-tetracyano-p-quinodimethane, E=tetracyanoethylene, are known to exhibit magnetic ordering resulting from magnetic interactions between the 3d metal orbitals of the paramagnetic metal ion and pi* orbitals of the organic radical spin centers. The reaction of THF solutions of UI3(THF)4 with neutral TCNQ and TCNE instantaneously produce insoluble coordination polymers that can be assigned a formula of [U(TCNX)2I2(THF)2]n on the basis of elemental analysis. Similar reactions between (K-18-crown-6)(TCNX) reagents and UI3(THF)4 produce materials with slightly different phase compositions that are structurally distinct from the neutral TCNQ and TCNE reaction products, as judged by infrared spectroscopy. In all cases the magnetic response of these materials is consistent with the presence of the U(IV) rather than U(III) ion. Voltammetric data obtained for all the synthetic precursors are consistent with the U(IV)/TCNX radical anion formulation. None of the materials undergo magnetic ordering, presumably due to the singlet magnetic ground state that results from the U(IV) ion in a low-symmetry ligand field.

Electron molecular ion recombination: Product excitation and fragmentation

Electron-ion dissociative recombination is an important ionization loss process in any ionized gas containing molecular ions. This includes the interstellar medium, circumstellar shells, cometary comae, planetary ionospheres, fusion plasma boundaries, combustion flames, laser plasmas and chemical deposition and etching plasmas. In addition to controlling the ionization density, the process generates many radical species, which can contribute to a parallel neutral chemistry. Techniques used to obtain rate data and product information (flowing afterglows and storage rings) are discussed and recent data are reviewed including diatomic to polyatomic ions and cluster ions. The data are divided into rate coefficients and cross sections, including their temperature/energy dependencies, and quantitative identification of neutral reaction products. The latter involve both ground and electronically excited states and including vibrational excitation. The data from the different techniques are compared and trends in the data are examined. The reactions are considered in terms of the basic mechanisms (direct and indirect processes including tunneling) and recent theoretical developments are discussed. Finally, new techniques are mentioned (for product identification; electrostatic storage rings, including single and double rings; Coulomb explosion) and new ways forward are suggested.

Apparatus for reactive cluster-surface studies

We present a new instrument that has been specifically designed for systematic studies of reactive cluster-surface collisions under well-defined ultrahigh-vacuum conditions. As a key feature, it incorporates a temperature-controlled, high-pressure cluster source with an unsurpassed pulse-to-pulse stability for the generation of weakly bound molecular aggregates. Impact processes can be investigated in two experimental configurations complementing one another: In the first, the exploration of intracluster reactions of accelerated, size-selected, positively or negatively charged cluster ions (1–100eV∕molecule) is accomplished, employing an inert target surface combined with angular-integrated ion detection. This arrangement uses a compact, homebuilt dual time-of-flight mass spectrometer with excellent mass resolution m∕Δm>2000 and postacceleration capabilities. In the second configuration, the detailed analysis of chemical reactions between neutral clusters and a well-defined single crystal at lower kinetic energies (0.01–1eV∕molecule) is possible. Here, the surface interaction of a seeded supersonic cluster beam is probed with angular-, time-, and velocity-resolved detection of neutral reaction products using a high-performance quadrupole mass spectrometer.

Neutral-particle emission in collisions of electrons with biomolecular ions in an electrostatic storage ring

Electron-biomolecular ion collisions were studied using an electrostatic storage ring with a merging electron beam device. Biomolecular ions produced by an electrospray ion source and accelerated to 20 keV/charge were injected into the ring after being mass-analyzed. The circulating ion beam was then merged with an electron beam. Neutral reaction products in collisions of electrons with ions were detected by a micro-channel plate outside of the ring. Electron-ion collisions were studied for multiply-deprotonated oligonucleotide and peptide anions as well as singly protonated oligonucleotide and peptide cations. For peptide cations, neutrals were resonantly emitted at an electron energy of around 6.5 eV, which was almost independent of the ion masses. This is deduced to come from electron-ion recombination, resulting in the cleavage of a peptide bond. For DNA oligonucleotide cations, resonant neutral particle emission was also observed. In electron and DNA anion collisions, neutrals started to increase from definite threshold energies, where the threshold energies increased in proportion to the ion charge. The same was found for peptide anions. The origin of this phenomenon is discussed.

Energy dissipation during desorption of reaction products: the role of substrate phonons

Abstract We discuss the processes of energy dissipation to substrate phonons that accompany desorption of neutral reaction products from catalyst surfaces. Employing the semiclassical trajectory approximation for description of the motion of desorbing particles on the product potential energy surface and assuming linear coupling to the phonon heatbath, we assess the mean number of excited phonons and the mean energy transfer for the paradigmatic Langmuir–Hinshelwood scenario of desorption of CO 2 from Pt(1 1 1), Pd(1 1 1) and Rh(1 1 1) surfaces.