Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C₆₀ fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C₆₀ fullerene, and can bind up to four hydrogen molecules with average adsorption energies of ?0.85, ?0.83, ?0.58, and ?0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 3, 4) are inside this window. The irreversible 2H₂ + NiC₆₀ and reversible 3H₂ + NiC₆₀ interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.     

DFT study of hydrogen storage in Pd-decorated C60 fullerene

Hydrogen storage reactions on Pd-doped C₆₀ fullerene are investigated by using the state-of-the-art density functional theory calculations. The Pd atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to four hydrogen molecules with average adsorption energies of 0.61, 0.45, 0.32, and 0.21 eV per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.8 wt%. While the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 1 are outside the department of energy (DOE) domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 2–4 are inside this domain. While the interaction of 1H₂ with Pd + C₆₀ is irreversible at 459 K, the interaction of 2H₂ with Pd + C₆₀ is reversible at 529 K. The hydrogen storage of the irreversible 1H₂ + Pd–C₆₀ and reversible 2H₂ + Pd–C₆₀ interactions are characterised in terms of densities of states, infrared, Raman, and proton magnetic resonance spectra, electrophilicity, and statistical thermodynamic stability.     

Extended X‐ray absorption fine structure and multiple‐scattering simulation of nickel dithiolene complexes Ni[S2C2(CF3)2]2n (n = −2, −1, 0) and an olefin adduct Ni[S2C2(CF3)2]2(1‐hexene)

A series of Ni dithiolene complexes Ni[S₂C₂(CF₃)]₂ⁿ (n = ?2, ?1, 0) ( 1 , 2 , 3 ) and a 1‐hexene adduct Ni[S₂C₂(CF₃)₂]₂(C₆H₁₂) ( 4 ) have been examined by Ni K‐edge X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine‐structure (EXAFS) spectroscopies. Ni XANES for 1 – 3 reveals clear pre‐edge features and approximately +0.7 eV shift in the Ni K‐edge position for `one‐electron' oxidation. EXAFS simulation shows that the Ni—S bond distances for 1 , 2 and 3 (2.11–2.16 Å) are within the typical values for square planar complexes and decrease by ～0.022 Å for each `one‐electron' oxidation. The changes in Ni K‐edge energy positions and Ni—S distances are consistent with the `non‐innocent' character of the dithiolene ligand. The Ni—C interactions at ～3.0 Å are analyzed and the multiple‐scattering parameters are also determined, leading to a better simulation for the overall EXAFS spectra. The 1‐hexene adduct 4 presents no pre‐edge feature, and its Ni K‐edge position shifts by ?0.8 eV in comparison with its starting dithiolene complex 3 . Consistently, EXAFS also showed that the Ni—S distances in 4 elongate by ～0.046 Å in comparison with 3 . The evidence confirms that the neutral complex is `reduced' upon addition of olefin, presumably by olefin donating the π‐electron density to the LUMO of 3 as suggested by UV/visible spectroscopy in the literature.     

Molecular Structures of H2X and D2X(X=0, S,Se, Te)

There are two possible configurations for H₂O, linear(D_∞h) or bent(C_2v). For a C_2v′, the three bands ν_1′ ν₂ and ν₃ should appear in both Raman and infrared. For a D_∞h. however, the ν₁, band should appear in only Raman and the ν₂ and ν₃ bands, in only infrared, that is, a principle of mutual exclusion of Raman and infrared should hold. The present author concludes that H₂X and D₂X(X=O, S, Se, Te) have a linear D_∞h. structure, since the obtained spectra show mutual exclusion of Raman and infrared.     

Structures and stabilities of endo- and exohedral Si20H20 derivatives: X@Si20H20 and XSi20H20, X = H + , H,N, P,C − , and Si −

Geometries, relative energies, and stabilities of endo- and exohedral complexes, X@Si₂₀H₂₀ and XSi₂₀H₂₀, (X = H⁺, H, N, P, C^?, and Si^?) are calculated at B3LYP/6-31G* level. The energy minimum structure of Si₂₀H₂₁ ⁺ shows that the proton cannot be positioned in the Si₂₀H₂₀ centre, but prefers attach to Si₂₀H₂₀ exohedrally with C_2v symmetry. Most investigated I_h endohedral complexes X@Si₂₀H₂₀ (X = H, N, P, C^?, and Si^?) are local minima, except for ²N@Si₂₀H₂₀, which is a high-order saddle point. Inclusions energies of the endohedral complexes are calculated, and it reveals that energy penalties caused by encapsulation are rather small. Exohedral complexes XSi₂₀H₂₀ (X = H, N, P, C^?, and Si^?) have C_2v or C_s local minima, and most of them are more stable than their endohedral isomers with the exception of C_2v ⁴PSi₂₀H₂₀ and ⁴Si^?Si₂₀H₂₀.     

A hydrogen bonded complex C2H2…HBr isolated and characterized in the gas phase using pulsed-jet,Fourier transform microwave spectroscopy

A complex formed from ethyne and hydrogen bromide has been isolated and characterized by using a fast-mixing nozzle in conjunction with a pulsed-jet, Fourier transform microwave spectrometer. Any possible chemical reaction between the two components when mixed in the usual way was thereby precluded. The rotational constants A, B and C, the quartic centrifugal distortion constants δ_J, δ_Jk and δ_J and the Br nuclear hyperfine coupling constants X_aa and X_bb—X_cc (nuclear quadrupole) and M_bb (spin-rotation) were determined for each of the five isotopomers C₂H₂…H⁷⁹Br, C₂H₂…H⁸¹ Br, C₂H₂…D⁷⁹Br, C₂H₂…D⁸¹Br and C₂D₂…H⁷⁹Br. Interpretations of the spectroscopic constants show that the complex is planar and T shaped in the equilibrium conformation, with HCCH internuclear axis forming the cross of the T and the HBr internuclear axis lying along the C₂ axis of C₂H₂. The H of HBr is closer to the centre (?) of the π bond of ethyne, and therefore HBr is involved in a hydrogen bond to the π system, in which the distance of H from ? is r (?…H) = 2.469(1) A. The intermolecular stretching force constant is estimated as kσ = 5.38(2) Nm^?1 for the species involving a hydrogen bond (C₂H₂…H⁷⁹Br, C₂H₂…H⁸¹Br and C₂D₂…H⁷⁹Br) while this quantity increases to kσ = 5.68(2)Nm^?1 for those complexes bound through a deuterium bond (C₂H₂…D⁷⁹Br and C₂H₂…D⁷⁹Br). The opportunity is taken to consider similarities in the properties of complexes within the two series B…HBr and B…HC1 for a range of Lewis bases B, including B = C₂H₂. Some family relationships are identified in the two series.     

Stability and Growth Modes of Ni--C Clusters: A Study based on All-Electron Density Function Theory

Growth modes of the free-standing NiCN （N ≤ 8） and Ni2CN （N ≤ 8） dusters are investigated by the allelectron density functional theory. The results reveal that there are two competing modes for the growth of these clusters： the linear chain and the ring structure without transannular bonds. The lowest-energy geometries of NiCN （N ≤ 8） are the linear chains with the Ni atom at one end, except for NiC2 and NiCT. The Ni2CN （N ≤ 8） clusters all prefer to the linear chains with the two Ni atoms at the two ends. Miilliken population analysis indicates that the total spin of the lowest-energy cluster show significant odd-even alternation. The NiMCN （M = 1,2） clusters with the even N are one and those with the odd-N are zero.     

Theoretical investigations on the spin Hamiltonian parameters and local structures for the trigonal Ni2+ centers in CsMgX3 (X=Cl,Br, I)

The spin Hamiltonian parameters (zero-field splitting and the anisotropic g factors) and the local structures for the trigonal Ni²⁺ centers in CsMgX₃ (X=Cl, Br, I) are theoretically investigated from the perturbation formulas of these parameters for a 3d⁸ ion in trigonally distorted octahedra, by including the ligand s-orbital contributions. Based on the studies, the local impurity-ligand bond angles β related to the C ₃ axis in the Ni²⁺ centers are found to be about 2° larger than the corresponding angles, β_H, in the hosts, due to the size mismatching substitution of Mg²⁺ by Ni²⁺. The theoretical results based on the inclusion of the ligand s-orbital contributions show an improvement when compared with those in the absence of the above contributions, especially for the ligand I^?.     

Characterizations of B and N heteroatoms as substitutional doping on structure,stability, and aromaticity of novel heterofullerenes evolved from the smallest fullerene cage C20: a density functional theory perspective

The structural stabilities and electronic properties of C₂₀ fullerene and some its incorporated boron and nitrogen derivatives are probed at B3LYP/AUG‐cc‐pVTZ level of theory. According to density functional theory results, the topology of inserted B or N heteroatoms in [20]‐fullerene perturbs strongly the stability, energy, geometry, charge, polarity, nucleus‐independent chemical shifts, aromaticity, and highest‐occupied molecular orbital and lowest‐unoccupied molecular orbital (HOMO–LUMO) gap of the resulting heterofullerenes. Vibrational frequency (υ_min) calculations show that except N₁₀C₁₀, all other B_bN_nC_{20‐(b + n)} heterofullerenes with b, and n = 0, 4, 5, 8, and 10 are true minima. The calculated band gaps (?E_HOMO–LUMO) of B₈C₁₂, and N₈C₁₂ (2.86 eV), show them the most stable heterofullerenes against electronic excitations. While 10 B substituting in equatorial position increase the conductivity of B₁₀C₁₀ through decreasing its band gaps, 10 N doping in equatorial position enhance stability of N₁₀C₁₀ against electronic excitations via increasing its band gaps. High natural bond orbital and Mulliken charge transfer on the surfaces of B atoms, especially B₅N₅C₁₀with five B–N bonds in the equatorial position, provokes further investigation on its possible application for hydrogen storage. Nucleus‐independent chemical shift values show that B₅N₅C₁₀ is the most aromatic species. The calculated heat of atomization per carbon (ΔH_at/C) of B₈C₁₂ shows it the most thermodynamic stable heterofullerenes of each. Copyright © 2016 John Wiley & Sons, Ltd.     

The reaction of acetylene with Ni(100) and Ni(110) surfaces at room temperature

Ultraviolet photoemission spectroscopy using hv = 21.2 eV and filtered 40.8 eV radiation as well as temperature programmed thermal desorption spectroscopy are used to investigate the chemical reaction of acetylene with Ni(100) and Ni(110) surfaces at room temperature. Striking crystallographic effects and several coexisting phases are observed and found to be coverage and temperature dependent. A methodology is described and used to predict the relative energy levels for a variety of adsorbed hydrocarbon fragments on Ni surfaces. Such levels together with the thermal desorption spectra are used to identify the observed species. In particular, CH and CCH species are isolated on Ni(100) and Ni(110) surfaces, respectively, via low temperature adsorption and subsequent pulsed sample warming experiments. The room temperature adsorption phases are deduced using these ionization levels together with those of chemisorbcd acetylene, atomic hydrogen and carbon. At room temperature on Ni(100), H, C, CH and C₂H₂ species form together below 2 L exposure while CH species form thereafter, up to a saturation exposure of ~10 L. On Ni(110), H and CCH species form below 1.5 L exposure followed by the formation of CH₂ and likely CH species. The relative stabilities of these species at elevated temperatures is: C₂H₂ < CCH ? CH < CH₂. A model for the bonding of acetylene and its reaction to form CCH species on Ni(110) is proposed.     

Structural and optical properties of the M@C59X cages (X=N,B and M=Li,Na)

Using B3LYP/6-31G* density functional level of theory, the structural and optical properties of the C₆₀ and M@C₅₉X cages have been investigated. Results indicate that the charge on C atoms and band gap of C₆₀ cage are changed dramatically with the substitution of one B or N atom at one of the C sites and the Li and Na atom encapsulations in the C₆₀ cage. The Mulliken analyses show that the charge is transferred completely between the alkali atoms and the C₅₉X cage. The substitutional and encapsulation doping (SED) reduce the optical gaps of the C₆₀ cage. Also, the oscillator strengths of the absorption peaks are dependent on dopant types.     

Substituent effects on the 13C NMR chemical shifts of the imine carbon in N‐(4‐X–benzylidene)‐4‐(4‐Y–styryl) anilines

Long‐range electronic substituent effects were targeted using the substituent dependence of δ_C(C═N), and specific cross‐interactions were explored extendedly. A wide set of N‐(4‐X–benzylidene)‐4‐(4‐Y–styryl) anilines, p‐X–C₆H₄CH═NC₆H₄CH═CHC₆H₄–p‐Y (X = NMe₂, OMe, Me, H, Cl, F, CN, or NO₂; Y = NMe₂, OMe, Me, H, Cl, or CN) were prepared for this study, and their ¹³C NMR chemical shifts δ_C(C═N) of C═N bonds were measured. The results show that both the inductive and resonance effects of the substituents Y on the δ_C(C═N) of p‐X–C₆H₄CH═NC₆H₄CH═CHC₆H₄–p‐Y are less than those of the substituents Y in p‐X–C₆H₄CH═NC₆H₄–p‐Y. Moreover, the sensitivity of the electronic character of the C═N function to electron donation/electron withdrawal by the substituent X or Y attenuates as the length of the conjugated chain is elongated. It was confirmed that the substituent cross‐interaction is an important factor influencing δ_C(C═N), not only when both X and Y are varied but also when either X or Y is fixed. The long‐range transmission of the specific cross‐interaction effects on δ_C(C═N) decreases with increasing conjugated distance between X and Y. The results of this study suggest that there is a long‐range transmission of the substituent effects in p‐X–C₆H₄CH═NC₆H₄CH═CHC₆H₄–p‐Y. Copyright © 2012 John Wiley & Sons, Ltd.     

A first-principles study on the adsorption behaviour of methanol and ethanol over C59B heterofullerene

In the present study, the adsorption behaviour of methanol (CH₃OH) and ethanol (C₂H₅OH) molecules over heterofullerene C₅₉B surface is studied by density functional theory calculations. This heterofullerene is obtained from C₆₀ by substituting a carbon atom with a boron atom and relaxing self-consistently the structure to the local minimum. The adsorption of CH₃OH and C₂H₅OH on the C₅₉B is exothermic and the relaxed geometries are stable. The CH₃OH and C₂H₅OH adsorption can also induce a change in the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gap of the nanocage. The dehydrogenation pathways of CH₃OH and C₂H₅OH via O–H and C–H bonds scission are also examined. The results indicate that O–H bond scission is the most favourable pathway on the C₅₉B surface.     

Hydrogen peroxide yield in gamma‐irradiated air-saturated ice at 77 °K

The concentration of hydrogen peroxide formed in thawed γ-irradiated air-saturated ice has been studied as a function of dose over the range: 3.8 × 10¹⁷ eV/ml-5.6 × 10¹⁹ eV/ml. The concentration dose data do not fit a linear plot. Three empirical equations have been tried to fit the experimental data. Of these equations, the one of the form C = [(1+αD) - 1]/β is found to fit the data very closely, and also predicts log C to vary linearly with log D at high doses as found experimentally. By extrapolation of this equation to zero dose G _H2O2 is evaluated to be 0.32.     

Theoretical characterization of axial deformation effects on hydrogen storage of Ti decorated armchair (5,5) SWCNT

Theoretical calculations have been performed in the framework of density functional theory to characterize the effect of axial deformation on hydrogen storage of Ti decorated armchair (5,5) SWCNT. The theoretical characterization has been carried out in terms of H₂ adsorption energies that are lying in the desirable energy window (?0.2 to ?0.6?eV) recommended by DOE, as well as a variety of physicochemical properties. A remarkable and significant change in H₂ adsorption energy is observed under the effect of only (1%) axial strain. Axial relaxation leads to H₂ adsorption energies within the recommended energy range for hydrogen storage, in contrast to axial compression. Simultaneous weakening of π and σ interactions, due to the effect of axial relaxation and loss of spatial orbital overlap, is in favor of hydrogen adsorption in the recommended energy range, and dominates the effect of charge transfer from Ti 3d to C 2p of the SWCNT. The calculated pairwise and non pairwise additive components confirm that the role of the SWCNT is not restricted to supporting the metal. Polarizability and hperpolarizabilty calculations as well as spectral analysis characterize the relaxed structure (Z?=?1.02), for which H₂ adsorption energy (?0.34?eV) is in the recommended energy range for hydrogen storage, to be energetically more preferable than the compressed structure (Z?=?0.99). The results offer a way to control and characterize the hydrogenation process of metal functionalized SWCNTs by strain loading.     

BeH,H2和BeH2的分子结构和势能函数

用二次组态相关(QCISD)和密度泛函(B3LYP)方法, 选用6-311++g(d,p), 6-311++g(3df,3pd)和D95(3df,3pd)基组对H₂, BeH和BeH₂分子的结构进行优化. 得到它们的基态电子态分别为H₂(¹Σ_g), BeH(²Σ)和BeH₂(¹Σ_{g 关键词： BeH 2}')" href="#">BeH₂ 2')" href="#">H₂ 二次组态相关(QCISD) 势能函数     

(H2O)6的稳定结构及异构过程研究

(H₂O)₆是形成三维立体结构的最小水分子团簇并具有能量较低的多个稳定异构体.本文利用从头计算方法研究了各稳定结构的异构化过程.(H₂O)₆的环状结构与最稳定结构的能量差0.31 eV为一个氢键的键能.水分子团簇的异构化是分子间氢键打开或重组的过程,不同异构体之间的转化每次只涉及一个氢键的打开或重组,异构化的能垒高度在0.07—0.21 eV之间. 关键词： 水分子团簇 2O)₆')" href="#">(H₂O)₆ 异构化过程 从头计算     

ESR spectroscopics study of radicals formed from methoxycarbonylcholine picrate hemihydrate

Abstract

The electron spin resonance of γ-irradiated single crystals of methoxycarbonylcholine picrate hemihydrate, C₇H₁₆NO₃ ⁺ · C₆H₂N₃O₇ ^? · ½ H₂O has been observed and analyzed for different orientations of the crystal in the magnetic field. The crystals have been investigated between 70 and 350 K. The spectra were found to be temperature independent and the radiation damage centers are attributed to – ?[Obar]OCH₃ and –CH₂CH₂O? radicals. The g and hyperfine coupling constants were found to be almost isotropic with an average, g = 2.0060, a _H1 = 4.4G for –CH₂CH₂O?, g = 2.0050, a _H2 = 3.5G for –CH₂CH₂O? and g = 2.0045, a _H = 3.5 G for –?[Obar]OCH₃. These values indicate a long-range coupling between the unpaired electron and H protons.     

Catalytic effect of water,water dimer,water trimer,HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2 on the isomerisation of HN(NO2)2 to O2NNN(O)OH: a mechanism study

In this article, the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH without and with catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄ and CH₃CH₂COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H₂O, (H₂O)₂ and (H₂O)₃)-assisted transition states, as well as different values of pK_a for H₂SO₄, HCOOH and CH₃CH₂COOH. Very interesting is also the fact that H₂SO₄-assisted reaction is the most favourable for the hydrogen transfer from HN(NO₂)₂ to O₂NNN(O)OH, due to the smallest pK_a (?3.0) value of H₂SO₄ than H₂O, HCOOH, H₂SO₄ and CH₃CH₂COOH, and also because of the largest ∠X???H???Y (the angle between the hydrogen bond donor and acceptor) involved in H₂SO₄-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH, the apparent activation energy of H₂SO₄-assisted channel also reduces by 9.6 kcal?mol^?1, indicating that H₂SO₄ can affect the isomerisation of HN(NO₂)₂ to O₂NNN(O)OH, most obvious among all the catalysts H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂.     

MgH2(110)表面Pd单原子催化氢脱附反应的第一性原理研究

本文采用第一性原理密度泛函理论计算研究了MgH₂(110)表面吸附单原子Pd后的氢脱附反应. 计算发现,在吸附一个Pd单原子后,MgH₂(110)表面氢脱附反应的能垒可以从1.802 eV显著地降低到1.154 eV,表明Pd单原子对于氢脱附具有很强的催化效应. 并且,Pd单原子催化还可以将氢脱附的温度从573 K显著地降低到了367 K,从而使MgH₂(110)表面的氢脱附反应更加容易和快速地发生. 此外,通过MgH₂(110)表面氢溢出机制的反向过程来讨论了氢脱附反应的微观过程. 该研究表明Pd/MgH₂薄膜在未来的实验中可作为良好的储氢材料.