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1.
J. Moc 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):247-252
Five doublet isomers of the Al3H2 cluster lying
within a narrow range of 5 kcal/mol, along with the isomerization transition
states connecting them, have been located with the coupled-cluster CCSD(T)
and DFT methods. The two most stable doublet structures, the C2v planar
including the two Hs bound terminally and C1 non-planar showing one H
in terminal site and the other in threefold site are found to be essentially
degenerate. Although the reaction of Al3 with H2 to yield
Al3H2 is found to be significantly exothermic, by 23.5 kcal/mol,
this hydrogenation is impeded by a considerable kinetic barrier of 16 kcal/mol. Our result is consistent with the observed
lack of reactivity of
Aln towards H2(D2) for n=3 under thermal conditions [3].
The quartet Al3H2 isomers are predicted to lie 16–21 kcal/mol higher
in energy than the doublet analogues. Further dimerization of
Al3H2 to form Al6H4 has also been examined.
Electronic supplementary material Supplementary Online Material 相似文献
2.
The optical Raman and photoluminescence (PL) spectra of the high-pressure hydrogenated fullerene C60 are studied at normal conditions and at high pressure. The Raman spectrum of the most stable hydrofullerene C60H36 contains a large number of peaks related to various isomers of this molecule. Comparison of the experimental data with the results of calculations shows that the most abundant isomers have the symmetries S6, T, and D3d. The Raman spectrum of deuterofullerene C60H36 is similar to that of C60H36, but the frequencies of the C-H stretching and bending modes are shifted due to the isotopic effect. The PL spectrum of hydrofullerene C60H36 is shifted to higher energies by approximately 1 eV with respect to that of pristine C60. The effect of hydrostatic pressure on the Raman and PL spectra of C60H36 has been investigated up to 12 GPa. The pressure dependence of the phonon frequencies exhibits peculiarities at approximately 0.6 and 6 GPa. The changes observed at approximately 0.6 GPa are probably related to a phase transition from the initial orientationally disordered body-centered cubic structure to an orientationally ordered structure. The peculiarity at approximately 6 GPa may be related to a pressure-driven enhancement of the C-H interaction between the hydrogen and carbon atoms belonging to neighboring molecular cages. The pressure-induced shift of the photoluminescence spectrum of C60H36 is very small up to 6 GPa, and a negative pressure shift was observed at higher pressure. All the observed pressure effects are reversible with pressure. 相似文献
3.
The recently measured heat of formation ΔH f o of C60F36(g) is submitted for extensive computational treatment. The computations are performed at the AM1, PM3 and SAM1 semiempirical quantum-chemical levels on a set of selected isomers, especially those of T, C 3, and D 3d symmetries. The SAM1 method produces somewhat lower values than PM3 and, in particular, AM1 (as is the case for pristine fullerenes). For example, the SAM1 computed value for the T isomer is ?1293 kcal/mol; i.e., it is within the experimental error. However, the issue of isomerism should also be taken into consideration accordingly and related kinetic aspects should be checked using computations. Even without these two additional steps being carried out, the agreement between the observed and computed values is encouraging. 相似文献
4.
J. Moc 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(3):309-317
We have explored the lowest doublet and quartet potential
energy surfaces (PES) for the reaction of gallium trimer with H2. This
reaction was studied experimentally by Margrave and co-workers in a noble
gas matrix. The detailed reaction paths ending up with the low-energy
Ga3H2 hydride isomers have been predicted based on the high level
ab initio coupled-cluster calculations (CCSD(T)) with large basis set. We
have found that the reaction occuring on the lowest doublet PES is described
by the activation barrier for H2 cleavage of about 15 kcal/mol,
consistent with experiment. In the most stable Ga3H2 hydride
structure, whose formation is exothermic by 15 kcal/mol, both H atoms assume
three-fold bridged positions. The diterminal planar structure of
Ga3H2, proposed experimentally from the observed IR spectra, is
found to be only 1 kcal/mol less stable than the dibridged form. 相似文献
5.
Formation of N‐sulfonylaziridines, N‐ethylidenesulfonamides, N‐vinylsulfonamides and 4,5‐dihydro‐1,2,3‐oxathiazole 2‐oxides by the reaction of singlet and triplet trifluoromethyl‐, methyl‐ and tosylnitrenes with ethylene is studied computationally at the B3LYP/6‐311++G(d,p) level of theory in both gas phase and in solution. Singlet sulfonylnitrenes react with ethylene via [1 + 2]‐cycloaddition exothermically to give N‐sulfonylaziridines. Triplet sulfonylnitrenes are formed from the singlet ones by the intersystem crossing with the energy barrier not exceeding 2.5 kcal/mol and react in a stepwise fashion by C‐addition or H‐abstraction. The C‐addition gives rise to the formation of N‐sulfonylaziridines or N‐ethylidenesulfonamides depending on the S―N―Csp3―Csp2 dihedral angle, with the barrier to rotation about the N―Csp3 bond not exceeding 2.5 kcal/mol. The H‐abstraction results in N‐vinylsulfonamides. Transformation of N‐sulfonylaziridines to N‐ethylidenesulfonamides requires to overcome the barrier of 57–60 kcal/mol, N‐ethylidenesulfonamides to 4,5‐dihydro‐1,2,3‐oxathiazole 2‐oxides—74–80 kcal/mol and N‐vinylsulfonamides to N‐ethylidenesulfonamides—about 64 kcal/mol. The use of the polarizable continuum model does not lead to a change of the course of the reaction of trifluoromethanesulfonylnitrene with ethylene and only slightly affects the relative energies of the products, intermediates and transition states. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
6.
Shogo Sakai Taro Udagawa Shohei Kato Keita Nakada 《Journal of Physical Organic Chemistry》2013,26(6):517-522
The mechanisms of the [2 + 2 + 2] cycloaddition reaction of three ethyne molecules were studied by ab initio molecular orbital and density functional methods. The transition states range from that of the concerted mechanism with D3h symmetry to that of the stepwise mechanism with C2 symmetry. The transition state structure and the activation energy depend on the basis set and computational method employed in the analysis. The activation energy barrier was determined to be in the range of 36–44 kcal/mol. The activation energy determined by various methods corresponds to the interaction energy, which is related to the electron correlation energy. The best estimation of the activation energy barrier is 41.6 kcal/mol, achieved from the relation between the interaction energy and the activation energy. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
The structure of a new allotropic form of carbon [C28]n having a simple cubic lattice and space group \(Pm \bar 3\) is proposed. The geometrical parameters of the building block of such a hypothetic crystal are preliminarily determined from DFT-PBE calculations of the cluster C8@(C20)8 and the polyhedral hydrocarbon molecule C8@(C20H13)8, in which the centers of the cubic clusters C8 coincide with the centers of the cluster C8@(C20)8 and of the molecule C8@(C20H13)8, respectively, and dodecahedral C20 carbon cages are located at the vertices of a cube. The energy of dissociation of the cluster C8@(C20)8 into a cubic cluster C8 and eight dodecahedral clusters C20 is calculated to be 1482 kcal/mol, and the energy of each C8-C20 bond is equal to 74.2 kcal/mol. The structure of the [C28]n crystal is refined using the DFT-PBE96/FLAPW method and optimized geometry. Calculations show that the crystal is a dielectric with an energy gap of 3.3 eV. The lattice parameter a of the crystal is equal to 5.6 Å, and its density is 3.0 g/cm3. The possible existence of analogous allotropic forms of elements Si and Ge is discussed. A method is proposed for designing a hypothetic allotropic form [C28]n from C20(CH3)8 molecules with T h symmetry. 相似文献
8.
Rodney Snooks Donald J. Arseneau Susan Baer Donald G. Fleming Masayoshi Senba James J. Pan Mee Shelley 《Hyperfine Interactions》1994,87(1):911-916
Thermal reaction rates for the gas-phase reaction Mu+C2H6MuH+C2H5 have been measured bySR over the temperature range 510–730 K. The usual Arrhenius expression,k=Aexp(–E
a
/RT), fits the data well, giving parametersA=1.0×10–9 cm3 molecule–1 s–1 andE
a
=15.35 kcal/mol. The activation energyE
a
is 5.5 kcal/mol higher than for the H atom variant of this reaction, indicating a marked difference in reaction dynamics. Preliminary analysis indicates a still greater difference between Mu and H for the corresponding CH4 reaction. 相似文献
9.
Pablo A. Denis 《Journal of Physical Organic Chemistry》2012,25(4):322-326
The addition of free radicals and the 1,3 dipolar cycloaddition onto pristine and lithium‐doped C60 were studied by means of the Perdew–Burke–Ernzerhof (PBE) and M06‐2X density functionals. In all cases, lithium increased the reactivity even though for the 1,3 dipolar cycloaddition onto C60 the change observed with respect to bare C60 was minimal. Both functionals employed gave similar encapsulation energies for Li@C60 namely, 33.1 and 38.2 kcal/mol at the PBE/6‐31G* and M06‐2X/6‐31G*, respectively. However, the increased reactivity because of lithium doping determined at the PBE level is smaller as compared with that computed with the M06‐2X functional, whereas that determined at the second‐order Møller–Plesset (MP2) level is the largest one. For example, using the M06‐2X functional the binding energy of fluorine to Li@C60 is 28.5 kcal/mol larger than that determined for C60, whereas at the PBE/6‐31G* level it is predicted to be increased by 24.7 kcal/mol. The results clearly suggest that Li@C60 is a much better free radical scavenger than C60. Finally, the complex hindered rotations of lithium inside C60 are expected to be strongly inhibited because lithium doping increases the well depth between the cage center and the equilibrium position near the addition site of the lithium atom. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
《Surface science》1993,294(3):L945-L951
This paper reports the results of a theoretical study of Na, H and C subsurface atomic species in nickel and demonstrates how these interstitial atoms influence the reactivity of the Ni(111) surface and the structure of carbon species adsorbed on the surface. The benzene molecule, C6H6, in planar and nonplanar geometries, is used to probe bonding at the surface. Adsorption energies are calculated by ab initio configuration interaction techniques modelling the surface as an embedded cluster. Adsorption energies of planar C6H6 at the most stable, three-fold, adsorption site are 18 kcal/mol for the Ni(111) surface, and 10, 19 and 44 kcal/mol in the presence of the Na, H and C interstitials, respectively. The energies required for the planar to puckered distortion are 99 kcal/mol on Ni(111), 69 kcal/mol with the Na interstitial, 83 kcal/mol with H, and 134 kcal/mol with C compared to 198 kcal/mol for distortion of C6H6 in the gas phase. The possible relevance of these results to the nucleation of diamond on nickel are discussed. The results indicate that subsurface Na stabilizes tetrahedrally bonded carbon subunits of the diamond structure while subsurface C may make it easier for the overlayer to revert to a planar graphite structure. 相似文献
11.
Two experimental values (?19.3 ± 0.3 and ?17.8 ± 0.1 kcal/mol) for the gas phase heat of formation (δfH) (298k) of nitromethane have been reported. Although these values differ by only 1.5 kcal/mol, substantially greater differences in theoretical and experimental results occur when these differing values are used to calculate thermodynamic properties. This is especially evident when these two values for the δfH of nitromethane are used to calculate thermodynamic properties of polynitro compounds. For example, when density functional theory (DFT) is coupled with the use of isodesmic reactions, the ΔfH of octanitrocubane is calculated to be 160.6 or 172.6 kcal/mol, depending on which value is used. It should also be appreciated that several computational theories depend upon having access to reliable experimental data for testing and development. We have examined this discrepancy using several computational models and several levels of theory. Our results coupled with a comprehensive review of the literature support the lower (?19.3 ± 0.3 kcal/mol) experimental value. This is problematic because the higher value (?17.8 ± 0.1 kcal/mol) has been used in the development and/or testing of several semiempirical quantum mechanical models as well as ab initio Gaussian theory (G2 and G3). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
New materials for hydrogen storage of Li-doped fullerene (C20, C28, C36, C50, C60, C70)-intercalated hexagonal boron nitrogen (h-BN) frameworks were designed by using density functional theory (DFT) calculations. First-principles molecular dynamics (MD) simulations showed that the structures of the C n -BN (n = 20, 28, 36, 50, 60, and 70) frameworks were stable at room temperature. The interlayer distance of the h-BN layers was expanded to 9.96–13.59 Å by the intercalated fullerenes. The hydrogen storage capacities of these three-dimensional (3D) frameworks were studied using grand canonical Monte Carlo (GCMC) simulations. The GCMC results revealed that at 77 K and 100 bar (10 MPa), the C50-BN framework exhibited the highest gravimetric hydrogen uptake of 6.86 wt% and volumetric hydrogen uptake of 58.01 g/L. Thus, the hydrogen uptake of the Li-doped C n -intercalated h-BN frameworks was nearly double that of the non-doped framework at room temperature. Furthermore, the isosteric heats of adsorption were in the range of 10–21 kJ/mol, values that are suitable for adsorbing/desorbing the hydrogen molecules at room temperature. At 193 K (–80 °C) and 100 bar for the Li-doped C50-BN framework, the gravimetric and volumetric uptakes of H2 reached 3.72 wt% and 30.08 g/L, respectively. 相似文献
13.
The binding energy of a hydrogen molecule on metal atoms (Li, Be, Na, and Mg) attached to aromatic hydrocarbon molecules (benzene
and anthracene) was calculated using an ab initio molecular orbital method at the MP2(FC)/cc-pVTZ level with basis set superposition
error (BSSE) correction. The energy tended to become more negative as the metal atom had a more positive charge and a smaller
radius. The energies of Li2C6H6-H2, Li2C14H10-H2, Na2C14H10-H2, and MgC14H10-H2 were −2.7 to −2.2, −4.0 to −3.1, −2.8 to −0.3, and −1.3 kcal/mol, respectively. Most of these energies were more negative
than those on the hydrocarbons without metal atoms (ca. −1 kcal/mol). Analyzing the Lennard–Jones type potential with the
parameters determined by the MP2 calculations, it was found that these energies mainly consisted of the induction force caused
by the positive charge of the metal atom and the dispersion force from the nearest C6-ring. The energy of BeC14H10-H2 was more negative (−8.6 kcal/mol) than of the other complexes. The hydrogen molecule in this complex had a comparatively
longer H–H distance and a more positive H2 charge than the others. These data suggest that the hydrogen adsorption on this complex involves a charge transfer process
in addition to physisorption interactions. The hydrogen binding energies in some Li2C14H10-H2 systems (∼−4.0 kcal/mol) and BeC14H10-H2 are promising to operate hydrogen storage/release at ambient temperature with moderate pressure. 相似文献
14.
A theoretical study on heavier group‐14 substituting effect on the essential property of formamide, strong hydrogen bond with water and internal rotational barrier was performed within the framework of natural bond orbital (NBO) analysis and based on the density functional theory calculation. For heavier group‐14 analogues of formamide (YHONH2, Y = Si, Ge and Sn), the nN–πY=O conjugation strength does not always reduce as Y becomes heavier, for example, silaformamide and germaformamide have similar strength of delocalization. Heavier formamides prefer being H‐bond donors to form FYO–H2O complexes to being H‐bond acceptors to form FYH–H2O complexes. The NEDA analysis indicates that H‐bond energies of FYO–H2O complexes increase as moving down group 14 due to concurrently stronger charge transfer (CT) and electrostatic attraction and for the FYH–H2O complexes H‐bond strengths are similar. The model of CTs from FYO to H2O differs from that at FYH–H2O complexes, which are contributed not only by aligning lone‐pair orbital of O but also by another lone‐pair orbital. At two lowest lying excited states (the triplet and S1 excited states), formamide and its heavier analogues form double H‐bonds with H2O molecule at the same time. The barrier heights of internal rotation become gradually low from C to Sn, formamide (15.73 kcal/mol) > silaformamide (11.73 kcal/mol) > germaformamide (9.45 kcal/mol) > stannaformamide (7.50 kcal/mol) at the CCSD(T)/aug‐cc‐pVTZ//B3LYP/cc‐pVTZ level. NBO analysis indicates that the barrier does not only come from the nN→π*YO conjugation, and for heavier analogues of formamide, the nN→σ*YO hyperconjugation effect and steric effect considerably contribute to the overall rotational barrier. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
Aiko Adamson Jean‐Claude Guillemin Peeter Burk 《Journal of Physical Organic Chemistry》2015,28(4):244-249
Hydrazine‐borane and hydrazine‐diborane contain, respectively, 15.4 and 16.9 wt% of hydrogen and are potential materials for hydrogen storage. In this work we present the gas‐phase complexation energies, acidities, and basicities of hydrazine‐borane and hydrazine‐bisborane calculated at MP2/6‐311 + G(d,p) level. We also report the release of dihydrogen from both protonated complexes (ΔGhydrazine‐borane = ?20.9 kcal/mol and ΔGhydrazine‐bisborane = ?27.2 kcal/mol) which is much more exergonic than from analogues amine‐boranes. The addition of the first BH3 to the hydrazine releases 17.1 kcal/mol, and the second addition releases 15.8 kcal/mol. The attachment of BH3 also increases the N―H acidity of hydrazine by 46.3 kcal/mol. It was found that the B―H deprotonation leads to intramolecular rearrangement. The basicity values for hydrazine‐borane and ‐bisborane are 180 and 172.8 kcal/mol, respectively. For both complexes the protonation centres are located at the boron moiety. The protonated structure of hydrazine‐bisborane is cyclic and can be described as H2 captured between a negatively charged B―H hydrogen and positive boron (B―H??H2??B). Atoms in molecules analysis are used to investigate bond paths in concerning structures. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
16.
K. P. Meletov S. Assimopoulos G. A. Kourouklis I. O. Bashkin 《Physics of the Solid State》2002,44(3):542-544
The effect of hydrostatic pressure on the photoluminescence and Raman spectra of hydrofullerene C60H36 was investigated for pressures up to 12 GPa at room temperature. The samples were synthesized by means of high-pressure hydrogenation. The pressure coefficients of the phonon modes were found to be positive and demonstrate singularities at ~0.7 and ~6 GPa. The pressure shift of the luminescence spectrum is unusually small and increases slightly at P≥6 GPa. All observed features are reversible with pressure, and C60H36 is stable in the pressure region investigated. 相似文献
17.
M.D. Ganji B. Abbaszadeh B. Ahaz 《Physica E: Low-dimensional Systems and Nanostructures》2011,44(1):290-297
We performed density functional theory calculations to investigate the possibility of formation of endohedrally H@(BN)n–fullerene (n: 24, 36, 60) and H@C60 complexes for potential applications in solid-state quantum-computers. Spin-polarized approach within the generalized gradient approximation with the Perdew–Burke–Ernzerhof functional was used for the total energies and structural relaxation calculations. The calculated binding energies show that H atom being incorporated into B60N60 nanocage can form most stable complexes while the B24N24 and C60 nanocages might form unstable complex with positive binding energy. We have also examined the penetration of an H atom into the respective nanocages and the calculated barrier energies indicate that the H atom prefers to penetrate into the B24N24 and B60N60 nanocages with barrier energy of about 0.47 eV (10.84 kcal/mol). Furthermore the binding characteristic is rationalized by analyzing the electronic structures. Our findings reveal that the B60N60 nanocage has fascinating potential application in future solid-state quantum-computers. 相似文献
18.
Gab‐Yong Lee 《Journal of Physical Organic Chemistry》2010,23(2):91-95
The substituent effect of electron‐withdrawing groups on electron affinity and gas‐phase basicity has been investigated for substituted propargyl radicals and their corresponding anions. It is shown that when a hydrogen of the α‐CH2 group or acetylenic CH in the propargyl system is substituted by an electron‐withdrawing substituent, electron affinity increases, whereas gas‐phase basicity decreases. The calculated electron affinities are 0.95 eV (CH?C? CH2?), 1.15 eV (CH?C? CHF?), 1.38 eV (CH?C? CHCl?), 1.48 eV (CH?C? CHBr?) for the isomers with terminal CH and 1.66 eV (CF?C? CH2?), 1.70 eV (CCl?C? CH2?), 1.86 eV (CBr?C? CH2?) for the isomers with terminal CX at B3LYP level. The calculated gas‐phase basicities for their anions are 378.4 kcal/mol (CH?C? CH2:?), 371.6 kcal/mol (CH?C? CHF:?), 365.1 kcal/mol (CH?C? CHCl:?), 363.5 kcal/mol (CH?C? CHBr:?) for the isomers with terminal CH and 362.6 kcal/mol (CF?C? CH2:?), 360.4 kcal/mol (CCl?C? CH2:?), 356.3 kcal/mol (CBr?C? CH2:?) for the isomers with terminal CX at B3LYP level. It is concluded that the larger the magnitude of electron‐withdrawing, the greater is the electron affinity of radical and the smaller is the gas‐phase basicity of its anion. This tendency of the electron affinities and gas‐phase bacisities is greater in isomers with the terminal CX than isomers with the terminal CH. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
Jochen Matthes Stephan Gründemann Gerd Buntkowsky Bruno Chaudret Hans Heinrich Limbach 《Applied magnetic resonance》2013,44(1-2):247-265
We have studied the o/p spin conversion of dihydrogen in contact with frozen solutions of Vaska’s complex Ir(CO)Cl(PPh3)2 (1) in C6D6 and with polycrystalline 1 at 77 K. The main purpose of this study was to elucidate the mechanism of this type of reactions found accidentally previously (Eisenschmid et al JACS 109:8089–8091, 1987 and Eisenberg ACS 24:110–116, 1991). The formation of p-H2 was followed after thawing of the samples by 1H nuclear magnetic resonance (NMR) spectroscopy at 298 K, where the oxidative addition of dihydrogen to 1 occurs leading to Vaska’s dihydride Ir(CO)ClH2(PPh3)2 (2) which is known to exhibit para-hydrogen-induced polarization (PHIP). The PHIP signal was shown to be proportional to the concentration of p-H2 as elucidated from the decrease of the signal of dissolved o-H2. The reaction was found to be faster for the frozen solution as compared to the polycrystalline powder. Optical microscopy showed that small particles of 1 are separated from the solution during the freezing process, exhibiting a larger surface area as compared to the polycrystalline powder. When a mixture of H2 and D2 was exposed to the frozen solutions or to the polycrystalline powder, the formation of HD was observed by 1H NMR. This finding indicates the presence of a chemical spin conversion involving two dihydrogen molecules. Additional 1H NMR experiments of dihydrogen in frozen C6D6 at 110 K indicated the formation of larger pores containing gaseous H2 as well as dihydrogen sites in interstitial sites between benzene molecules. Moreover, in the presence of 1, a signal at ?4.5 ppm was observed which was attributed to a dihydrogen in close contact with Ir. 相似文献
20.
A. S. Komolov E. F. Lazneva N. B. Gerasimova Yu. A. Panina A. V. Baramygin G. D. Zashikhin 《Physics of the Solid State》2016,58(6):1257-1261
The results of the investigation of the electronic structure of the conduction band in the energy range 5–25 eV above the Fermi level EF and the interfacial potential barrier upon deposition of aziridinylphenylpyrrolofullerene (APP-C60) and fullerene (C60) films on the surface of the real germanium oxide ((GeO2)Ge) have been presented. The content of the oxide on the (GeO2)Ge surface has been determined using X-ray photoelectron spectroscopy. The electronic properties have been measured using the very low energy electron diffraction (VLEED) technique in the total current spectroscopy (TCS) mode. The regularities of the change in the fine structure of total current spectra (FSTCS) with an increase in the thickness of the APP-C60 and C60 coatings to 7 nm have been investigated. A comparison of the structures of the FSTCS maxima for the C60 and APP-C60 films has made it possible to reveal the energy range (6–10 eV above the Fermi level EF) in which the energy states are determined by both the π* and σ* states and the FSTCS spectra have different structures of the maxima for the APP-C60 and unsubstituted C60 films. The formation of the interfacial potential barrier upon deposition of APP-C60 and C60 on the (GeO2)Ge surface is accompanied by an increase in the work function of the surface Evac–EF by the value of 0.2–0.3 eV, which corresponds to the transfer of the electron density from the substrate to the organic films under investigation. The largest changes occur with an increase in the coating thickness to 3 nm, and with further deposition of APP-C60 and C60, the work function of the surface changes only slightly. 相似文献