Thermal reactions of ethane-d6–acetylene and D2–acetylene mixtures behind shock waves

A study of the thermal decomposition of an acetylene–ethane-d₆ mixture indicates that the rate constant for hydrogen abstraction from acetylene by methyl is more than 20 times less than for abstraction from ethane. Isotopic exchange is initiated by a rapid reaction between product D atoms and C₂H₂. A series of experiments involving the reactions of a D₂–acetylene mixture indicated that a molecular exchange process was also occurring, and it was shown that d[C₂HD]/dt = k[D₂]^0.7[C₂H₂]^0.3, effective activation energy = 15.8 kcal/mol. This mechanism made an insignificant contribution to isotope exchange in C₂H₂–C₂D₆ mixtures.     

Processing of Oil Refinery Gases: Oxidative Dehydrogenation of the Ethane–Ethylene Fraction

Oxidative transformations of the ethane–ethylene fraction of oil refinery gases, containing 20 vol % C₂H₄, on VMoTeNb oxide catalyst in the temperature interval 330–450°C were studied. Comparison with oxidative transformations of the individual components (oxidative dehydrogenation of C₂H₆ and oxidation of C₂H₄) shows that ethylene does not noticeably influence the ethane conversion, whereas ethane strongly suppresses the ethylene conversion. The maximal yield of ethylene from the ethane–ethylene fraction is close to that reached in oxidative dehydrogenation of ethane under similar conditions and amounts to 70–72%.     

Acetone cation chemistry under varying electron density conditions: from unimolecular decomposition to dissociative recombination processes

The chemistry of ionized acetone:Ar mixtures under varied ionizing electron density conditions has been studied using matrix‐isolation techniques. Gaseous acetone diluted in excess argon gas was subjected to electron bombardment with 300 eV electrons at currents between 20 and 200 μA. Linear wire ‘pin’ and metal ‘plate’ electron collector geometries were employed, allowing a wide range of electron density conditions to be explored. The products of subsequent reaction processes were matrix isolated and analyzed by Fourier transform infrared absorption spectroscopy. Products included methane, ketene, 1‐propen‐2‐ol (the enol isomer of acetone), CO, HCO, ethane, ethane, acetylene and CCCO. Product absolute and relative yields varied with acetone number density, the choice of anode geometry and the rate of electron bombardment. The overall chemistry observed is rationalized in terms of mechanistic steps involving unimolecular cation decomposition, ion–molecule reactions, radical–radical reactions and dissociative recombination processes. Copyright © 2013 John Wiley & Sons, Ltd.     

Fourier transform infrared matrix-isolation analysis of acetaldehyde fragmentation products after charge exchange with Ar•+ under varied ionization density conditions

The products of the Ar^?+ charge exchange ionization of acetaldehyde have been isolated and compared with related photoionization results and computational work. Acetaldehyde has been used to assess the effect of varied ion density in the ionization region of the electron bombardment matrix isolation apparatus. The amount of acetaldehyde destruction has been measured for constant gas‐sample composition and constant ionization current for two anode geometries: a pin anode and a plate anode. For the same ionization current, a pin‐shaped anode demonstrates higher precursor molecule destruction efficiency (85%) than the plate‐shaped anode (30%), resulting in substantial effect on the yield and quantity of isolated products. When the plate anode is used, the observed infrared products correspond to matrix‐isolated carbon monoxide (CO), methane (CH₄), ketene (CH₂CO), ethynyloxy radical (HCCO), formyl radical (HCO^?), acetyl radical (CH₃CO^?), vinyl alcohol (H₂C = CH‐OH), and cationic proton‐bound dimer, Ar₂H⁺. When the pin anode is used, the same products are observed with different relative proportions and new absorption features corresponding to dicarbon monoxide (CCO) and methyl radical (CH₃^?) are observed. The surprising observation of infrared absorptions corresponding to vinyl alcohol along with low yield of products anticipated through the analysis of photoelectron–photoionization coincidence measurements suggests that the initially formed fragmentation products are able to further react within the matrix‐isolation environment to influence observed product yields. Related experiments, using the isotopomer CD₃CHO, suggest that the observed products are formed via radical–radical reactions that occur under the high pressure conditions of the matrix isolation environment. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation on stabilities and spectroscopy of C80O2 based on C80 (D5d) using density functional theory

The relative stabilities of the 17 possible isomers for C₈₀O₂ based on C₈₀ (D_5d) were studied using Becke three parameters plus Lee, Yang, and Parr's (B3LYP) method and 6‐31G (d) basis set in density functional theory. The most stable geometry of C₈₀O₂ was predicted to be 23,24,27,28‐C₈₀O₂ (A) with annulene‐like structures, where the additive bonds are those between two hexagons (6/6 bonds) near the equatorial belt of C₈₀ (D_5d). Electronic spectra of C₈₀O₂ isomers were calculated based on the optimized geometries using intermediate neglect of differential overlap (INDO) calculation. Compared with those of C₈₀ (D_5d), the first absorptions in the electronic spectra of C₈₀O₂ are blue‐shifted owing to the wide energy gaps. ¹³C nuclear magnetic resonance spectra and nucleus independent chemical shifts of the C₈₀O₂ isomers were computed at B3LYP/6‐31G level. The chemical shifts of the bridged carbon atoms in the epoxy structures of C₈₀O₂ compared with those of the bridged carbon atoms in the annulene‐like structures are changed upfield. Generally, the isomers with the annulene‐like structures of C₈₀O₂ are more aromatic than those with the epoxy structures. The addition of the oxygen atoms near the pole of C₈₀ (D_5d) is favorable to improving the aromaticities of C₈₀O₂. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Specific Processes and Scrambling in the Dehydrogenation of Ethane and the Degenerate Hydrogen Exchange in the Gas‐Phase Ion Chemistry of the Ni(C,H3,O)+/C2H6 Couple

A mechanistically unprecedented situation characterizes the gas‐phase ion chemistry of Ni(C,H₃,O)⁺ when reacted under thermal, single‐collision conditions with ethane. A dehydrogenation channel leading to Ni(C₃,H₇,O)⁺ is to 90% preceded by a complete loss of positional identity of all nine H‐atoms of the encounter complex (‘scrambling’), whereas ca. 10% of the reaction exhibit a selective C? H bond activation of the alkane. In addition, a degenerate H exchange between ethane and the (C,H₃,O) unit occurs as a side reaction, the mechanistic details of which remain unknown for the time being.     

Theoretical studies on a possible synthesis reaction pathway on N8 (CS) clusters

The potential energy surfaces of N₈ clusters were investigated by density functional theory (DFT) and a possible synthesis reaction pathway for N₈ (C_S) was suggested. The species involved were fully optimized up to the B3LYP/6‐311+G* level of theory. Relative energies were further calculated at the QCISD/6‐311+G*//B3LYP/6‐311+G* level. The reaction rate constants of these steps from the 1 (N₅⁺?N₃^?, complex, C_S) to 2 (N₈, C_S), 2 (N₈, C_S) to 3 (N₈, C_S), 3 (N₈, C_S) to 4 (N₈, D_2d), and 4 (N₈, D_2d) to 5 (N₈, C_S) reactions were predicted by the VTST theory. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1334–1339, 2001     

First principles study of the structure,electronic state,and stability of CmN2 clusters

Geometric and electronic properties of C_mN₂ (m = 1–14) clusters have been investigated by density functional theory using the hybrid B3LYP functional and the 6‐311G(d) basis set. Harmonic frequencies for these clusters are given to aid in the characterization of the ground states. These results show that C_mN₂ (m = 1–14) clusters form linear structures with D_∞h symmetry. Two N atoms favor to bond at ends in linear isomers. The chains with odd m have triplet ground states whereas the ones with even m have singlet ground states. The calculated HOMO–LUMO gaps and ionization potentials all show that the C_mN₂ (m = 1–14) clusters with even m are more stable than those with odd m, which is consistent with the observed even–odd alternation of the time‐of‐flight signal intensities. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Interfacial Enhancement by γ‐Al2O3 of Electrochemical Oxidative Dehydrogenation of Ethane to Ethylene in Solid Oxide Electrolysis Cells

Oxidative dehydrogenation of ethane (ODE) is limited by the facile deep oxidation and potential safety hazards. Now, electrochemical ODE reaction is incorporated into the anode of a solid oxide electrolysis cell, utilizing the oxygen species generated at anode to catalytically convert ethane. By infiltrating γ‐Al₂O₃ onto the surface of La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ‐Sm_0.2Ce_0.8O_2‐δ (LSCF‐SDC) anode, the ethylene selectivity reaches as high as 92.5 %, while the highest ethane conversion is up to 29.1 % at 600 °C with optimized current and ethane flow rate. Density functional theory calculations and in situ X‐ray photoelectron spectroscopy characterizations reveal that the Al₂O₃/LSCF interfaces effectively reduce the amount of adsorbed oxygen species, leading to improved ethylene selectivity and stability, and that the formation of Al‐O‐Fe alters the electronic structure of interfacial Fe center with increased density of state around Fermi level and downshift of the empty band, which enhances ethane adsorption and conversion.     

A gas phase study of the ions and [C3H3]− generated from the reaction of with propyne

It is reported that ions gererated in the gas phase by dissociative electron attachment to nitrous oxide react with propyne-d₃ (trideuteromethyl acetylene) to yield the ions ?D?C?C H, ?D₂? C?C^?, ^?CD₂C?CH and CD₃C?C^?. From their differing reactivity with methyl formate it is suggested that these four ions are distinct stable species.     

Perimeter Effects on Ring Currents in Polycyclic Aromatic Hydrocarbons: Circumcoronene and Two Hexabenzocoronenes

Current‐density maps are calculated at an ab initio level for the three symmetrical polycyclic aromatic hydrocarbons, circumcoronene [ 1 (D_6h)], hexabenzo[bc,ef,hi,kl,no,qr]coronene [ 2 a (D_6h) and 2 b (D_3d)], and hexabenzo[a,d,g,j,m,p]coronene [ 3 a (D_6h), 3 b (D₆) and 3 c (D_3d)], all of which can be formally derived by annelation of benzene rings to a coronene core. Whilst 1 is planar, 2 has a non‐planar minimum that is effectively isoenergetic with its planar form, and 3 has a well defined non‐planar structure. The shape of the molecular boundary rather than the planarity of the molecule plays the critical rôle in the character of the predicted currents. Formal deletion of outer hexagons from circumcoronene ( 1 ) in two different ways produces either hexabenzocoronene 2 with a prediction of disjoint local benzenoid diatropic currents linked by a global perimeter, or 3 with a giant diatropic perimeter current enclosing a weak paramagnetic circulation on the central hexagon. The current density map of 1 is effectively a superposition of those of 2 and 3 . Its strong diatropic perimeter current subsumes the six weaker diatropic benzenoid circulations evident in 2 , and bifurcates in the six outer benzenoid rings that form the corners of the giant hexagon; its benzene “hub” sustains a diatropic current, as would be expected from the partial cancellation of the strong diatropic hub current of 2 by the weaker paratropic hub current of 3 . The relationship between the three molecules is rationalised by considering orbital contributions to their current density maps.     

A CAS study on S‐loss and O‐loss dissociation mechanisms of the SO2+ ion in the C,D, and E states

In the present work, we mainly study dissociation of the C ²B₁, D²A₁, and E²B₂ states of the SO₂⁺ ion using the complete active‐space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods. We first performed CASPT2 potential energy curve (PEC) calculations for S‐ and O‐loss dissociation from the X, A, B, C, D, and E primarily ionization states and many quartet states. For studying S‐loss predissociation of the C, D, and E states by the quartet states to the first, second, and third S‐loss dissociation limits, the CASSCF minimum energy crossing point (MECP) calculations for the doublet/quartet state pairs were performed, and then the CASPT2 energies and CASSCF spin‐orbit couplings were calculated at the MECPs. Our calculations predict eight S‐loss predissociation processes (via MECPs and transition states) for the C, D, and E states and the energetics for these processes are reported. This study indicates that the C and D states can adiabatically dissociate to the first O‐loss dissociation limit. Our calculations (PEC and MECP) predict a predissociation process for the E state to the first O‐loss limit. Our calculations also predict that the E²B₂ state could dissociate to the first S‐ and O‐loss limits via the A²B₂ ← E²B₂ transition. On the basis of the 13 predicted processes, we discussed the S‐ and O‐loss dissociation mechanisms of the C, D, and E states proposed in the previous experimental studies. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Time-resolved mass spectrometric study of the reaction H + Trans-2-Butene

The title reaction was studied in a discharge flow system using mass flow and modulated molecular beam sampling with phase-sensitive detection in order to obtain time-resolved mass spectrometric analysis. At total conversion exceeding 30%, the major products are methane and ethane when initially hydrogen atoms are in excess; when butene is in excess, the major products are ethane and propylene. No hydrocarbons with more than 4 carbon atoms were detected in the products. The reaction is a complicated one since the simplest reaction scheme that successfully simulates the experimental results comprises 20 elementary reactions. The simulation, coupled with sensitivity analysis, shows that with hydrogen atoms in excess, significant amounts of propylene formed in the initial decomposition of the butyl radical react further with hydrogen atoms to form methane and ethane. When butene is in excess, approximately [C₃H₆] ≈ [CH₄] + ½[C₂H₆] which means that this propylene does not react further and almost all methyl radicals end up as CH₄ or C₂H₆. At small conversion, simulation shows that the major product by far is propylene regardless of the [H]/[butene] ratio. The absence of higher hydrocarbons in the products is at variance with earlier results of Rabinovitch and coworkers; however the present work leads to a comparable value for the average rate constant ??_a = ωD/S where D and S is the amount of products arising from the decomposition and stabilization, respectively, of the butyl radical and ω is the collision frequency.     

Photoionization and Pyrolysis of a 1,4‐Azaborinine: Retro‐Hydroboration in the Cation and Identification of Novel Organoboron Ring Systems

The photoionization and dissociative photoionization of 1,4‐di‐tert‐butyl‐1,4‐azaborinine by means of synchrotron radiation and threshold photoelectron photoion coincidence spectroscopy is reported. The ionization energy of the compound was determined to be 7.89 eV. Several low‐lying electronically excited states in the cation were identified. The various pathways for dissociative photoionization were modeled by statistical theory, and appearance energies AE_0K were obtained. The loss of isobutene in a retro‐hydroboration reaction is the dominant pathway, which proceeds with a reverse barrier. Pyrolysis of the parent compound in a chemical reactor leads to the generation of several yet unobserved boron compounds. The ionization energies of the C₄H₆BN isomers 1,2‐ and 1,4‐dihydro‐1,4‐azaborinine and the C₃H₆BN isomer 1,2‐dihydro‐1,3‐azaborole were determined from threshold photoelectron spectra.     

Preferential Formation of Mono‐Metallofullerenes Governed by the Encapsulation Energy of the Metal Elements: A Case Study on Eu@C2n (2n=74–84) Revealing a General Rule

Encapsulating one to three metal atoms or a metallic cluster inside fullerene cages affords endohedral metallofullerenes (EMFs) classified as mono‐, di‐, tri‐, and cluster‐EMFs, respectively. Although the coexistence of various EMF species in soot is common for rare‐earth metals, we herein report that europium tends to prefer the formation of mono‐EMFs. Mass spectroscopy reveals that mono‐EMFs (Eu@C_2n) prevail in the Eu‐containing soot. Theoretical calculations demonstrate that the encapsulation energy of the endohedral metal accounts for the selective formation of mono‐EMFs and rationalize similar observations for EMFs containing other metals like Ca, Sr, Ba, or Yb. Consistently, all isolated Eu‐EMFs are mono‐EMFs, including Eu@D_3h(1)‐C₇₄, Eu@C_2v(19138)‐C₇₆, Eu@C_2v(3)‐C₇₈, Eu@C_2v(3)‐C₈₀, and Eu@D_3d(19)‐C₈₄, which are identified by crystallography. Remarkably, Eu@C_2v(19138)‐C₇₆ represents the first Eu‐containing EMF with a cage that violates the isolated‐pentagon‐rule, and Eu@C_2v(3)‐C₇₈ is the first C₇₈‐based EMF stabilized by merely one metal atom.     

Theoretical study of two C50H40 isomers with three dodecahedrane cages sharing two pentagons

Structures, energies, and vibrational frequencies have been calculated for two C₅₀H₄₀ isomers with three dodecahedrane cages sharing two pentagons at the B3LYP/6‐31G* level of theory. Thus, two C₅₀H₄₀ isomers have the form of coplanar tri‐dodecahedrane‐cage molecules. The symmetry of one isomer is D_5d and that of another is C_2V. Heats of formation and vertical ionization energies for two C₅₀H₄₀ isomers have been estimated in this study. Heats of formation as well as vibrational analysis indicate that two C₅₀H₄₀ isomers enjoy sufficient stability to allow for its experimental preparation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Twisted Surfaces in Porous Single Crystals to Deliver Enhanced Catalytic Activity and Stability

Porous single crystals which combine ordered lattice structures and disordered inter‐connected pores would provide an alternative to create twisted surface in porous microstructures. Now, transition‐metal nitride Nb₄N₅ and MoN single crystals are grown on a 2 cm scale to create well‐defined active structures at twisted surfaces. High catalytic activity and stability toward non‐oxidative dehydrogenation of ethane to ethylene is observed. Unsaturated metal–nitrogen coordination structures including Nb‐N_1/5, Nb‐N_2/5, Mo‐N_1/3, and Mo‐N_1/6 at the twisted surface mainly account for the C?H activation with chemisorption of H in molecular ethane at the twisted surface, which not only improves dehydrogenation performance but also avoids the deep cracking of ethane to enhance coking resistance. 11–25 % ethane conversion and 98–99 % ethylene selectivity is demonstrated without degradation being observed even after the operation of 50 hours.     

Ionization potential of excited states of Be‐like sequence in the concept of iso‐spectrum‐level series

With the introduction of the concept of the iso‐spectrum‐level series, a linear relationship is found between the first differences of the ionization potential of excited states and nuclear charge Z along an iso‐spectrum‐level series, and the ionization potential of excited states of Be‐like sequence are studied systematically on the basis of the weakest bound electron potential model theory. The expression of nonrelativistic ionization potential is derived from the weakest bound electron potential model theory, and relativistic effects are included by using a fourth‐order polynomial in Z. As a demonstration, the ionization potentials of [He]2s2p ³P, [He]2s3s ¹S₀, [He]2s3p ¹P, [He]2s3d ¹D₂, and [He]2s4d ¹D₂ series for a range of Be‐like sequence from Z = 4–23 are calculated. The results are compared with the experimental data and the recent sophisticated ab initio results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 344–350, 2003     

CH bond activation in the presence or absence of oxygen or nitrous oxide

The reaction of C₂H₆with lattice oxygen, O^2- (in the absence of gaseous oxygen), or “adsorbedℍ oxygen (in the presence of gaseous oxygen) over NiMoO₄ catalysts has been performed and compared to C₃H₈ activation. The results obtained indicate that adsorbed oxygen exhibits a higher reactivity to C₂H₆, while lattice oxygen is more reactive relative to C₃H₈. Kinetic studies of these two reactions in presence of molecular oxygen have indeed shown that the ethane oxidative dehydrogenation (ODH) is dependent on the oxygen partial pressure, whilst on the contrary propane ODH is not. In order to confirm the presence of “adsorbed” oxygen for ethane activation, ODH tests have been performed with N₂O. On increasing temperature, the O^- adsorbed species enhances the mild oxidation of ethane. The activation energy of ethane consumption E_C2H6, relative to propane (E_C3H8 = 133 kJ/mol) is 145 kJ/mol. A possible mechanism is proposed for the oxidative dehydrogenation of ethane. This revised version was published online in August 2006 with corrections to the Cover Date.